HVAC fan on vs auto

[Chris Redmond]

The second floor on our home is a hot spot that takes much longer to cool than our basement/first floor. May be partly explained by the furnace and blower being in the basement, and our AC unit is older. No duct work in the attic, but some run through exterior walls.

We tried keeping the fan on all the time and is appears to help cool the upstairs faster than having the fan set to auto. I found conflicting info on whether or not keeping the fan on all the time affects the life of the fan, if doing this results in higher or lower bills, and also read some fans aren't meant to be on all the time.

Any thoughts on whether this is a good way to handle hot spots on the second floor, or any other suggestions? I couldn't find this on any other posts in this forum.

Also wondering if multiple thermostats in a home is a good way to go?

 

[WorthFlorida]

Unless you have an air handler in the attic or on the second floor, the second floor will always be warmer. Running in "Fan" mode is a good way to circulate the heat off the second floor (even in winter) and distribute it to the lower levels. I had a home in Illinois t=and the cold air returns were on the wall near the ceiling and it helped. My Syracuse home, when built I had the air returns placed high on the wall from the normal place at the floor.

My current 2 story home in Orlando, Florida the air handler is on the second floor. Helps bigtime keep the two floors nearly the same temperature but the biggest improvement to comfort was when I changed the thermostat to a Honeywell WiFi Smart thermostat. It has a fan feature called "Circulate" plus "Auto" and "On". I keep it in circulate mode 24/7. About a minimum of 35 minutes per hour, the fan runs in conjunction with the cooling and heating demands. Occasionally I'll change it to auto mode such as when opening windows and if I forget to change it back, the upstairs is much warmer. The fan uses very little power and you'll hardly notice a difference on th eelectric bill.

Honeywell has several models, this is the one I have. I bought it three years ago and it was $189. https://www.homedepot.com/p/Honeywell-Home-Wi-Fi-Smart-Thermostat-RTH9580WF/203926327. It is an excellent unit. Honeywell now has a T9 model (about a year old) that can be used with remote sensors and it can be programmed to which sensor to use for different times of the day and a person sensor. It is essentially a multi room thermostat. You read up on it on Honeywell site.

Most homes up north with forced air systems use the wall stud cavity as the cold air return or the grill is at the floor level. The floor plate is cut out all the way to the basement and sometimes the floor joist is covered in sheet metal to create a duct to get to the furnace. The supply side is always via duct work. If your returns on the second floor use the stud cavity, it is very easy to move the grills up on the wall near the ceiling (to pull the excess heat off), by opening up the drywall, move the grill and patching the drywall at the floor. It won't be perfect but it will help

 

[Sponsor]

 

[Dana]

The second floor on our home is a hot spot that takes much longer to cool than our basement/first floor. May be partly explained by the furnace and blower being in the basement, and our AC unit is older. No duct work in the attic, but some run through exterior walls.

Using exterior walls as a duct chase is in some ways worse than ducts in attics, since it creates a basement-to-attic (or near-attic) convection path. If the ducts are well sealed to the studs, sheathing and drywall at every floor boundary that can be mitigated, but it also means a gap in the wall insulation, and in winter that means the hottest air in the house (115F - 140F air in the supply duct) is in close proximity to the cold wall sheathing.

We tried keeping the fan on all the time and is appears to help cool the upstairs faster than having the fan set to auto. I found conflicting info on whether or not keeping the fan on all the time affects the life of the fan, if doing this results in higher or lower bills, and also read some fans aren't meant to be on all the time.

If it's the same air handler blower used for both heating and cooling it's a very durable component capable of a very high duty cycle- it's more likely that the heat exchanger in the furnace or the AC system will die of other causes before the blower fails. But there are other good reasons NOT to run the fan continuously such as:

* When the cooling cycle ends there is still moisture on the cooling coil that has been taken from the air. Running the fan puts that moisture back into the indoor air as the coil warms up between cooling cycles.

* No duct system is perfectly balanced or perfectly tight. When the air handler is running it generates pressure differences between rooms, and pressure differences between the rooms and "The Great Outdoors". A room that end up positively pressured to the outdoors when the air handler is running drives dry cooled air to the outdoors through every available local leak path, and rooms that are negatively pressurized relative to the outdoors suck in hot humid outdoor air when the air handler is running.

* A typical split capacity blower motor uses 600-1000 watts, which is the equivalent to running a 600-1000 watt space heater.

The sum total of these effects is a measurably increased net cooling load, and lower cooling efficiency.

Any thoughts on whether this is a good way to handle hot spots on the second floor, or any other suggestions? I couldn't find this on any other posts in this forum.

Under the heading "other suggestions":

Start by improving the overall flow. If there are any doored off rooms in the house, but particularly rooms on the second floor that have supply registers but no return registers need to have retrofit return paths- a door cut at the threshold is not enough. I've posted multiple responses on this forum on how to make "jump duct" returns, as well as tips on duct sealing, sealing the duct boots to the wall/ceiling/floor etc., and how to measure the room to room pressure differences.

Tighten up the house to reduce the air handler driven parasitic loads. I've also posted a fair amount on [0]=31486']air sealing the house too.

To the extent possible, lower the cooling load to the second floor. Measure the ceiling temperature in several spots with a pistol grip IR thermometer (a $50-75 box store version is fine). If the difference between the ceiling temp and floor temp is more than 3F you're probably below the IRC prescriptive code-min R49 for climate zone 5 (which includes the northern half of OH), and may even be below the prior code-min R39. If you don't have at least 10" of insulation in the attic, add some, but do it right. (If you're going there I can lend a lot more detail, if you like.) No matter what, air sealing the attic floor/upper floor ceiling is a first and all-important step prior to adding insulation to the attic.

If the existing insulation is fiberglass (blown or batt) it's not doing nearly as much as it should for blocking heat from the attic. Fiberglass is somewhat translucent in the deep infra-red range, the heat that is being radiated from a hot roof deck, and the low density fiberglass in most attics is also not very air retardent. When the roof deck is hot the temperature of the fiberglass an inch from the top can even exceed the air temperature in the attic by a few degrees, which means you're insulating against a higher temp with an inch less insulation. And during the heating season convective loops between the cold attic and fiberglass cause it to underperform it's R value on the coldest nights of the year. Both of the IR and air retardency/convection issues can be significantly rectified by overtopping the with as little as 3" of blown cellulose, which is opaque to IR radiation, and even at 1.2-1.5lbs per cubic foot open-blown density is more than an order of magnitude more air retardent than an R19 batt.

Also wondering if multiple thermostats in a home is a good way to go?

Retrofit zoning by floor in a ducted air HVAC system can get complicated, but it's do-able. In most homes it's possible to run it as a single zone if the equipment is right-sized for the load, not so much if the systems are (all too commonly) 3x or more oversized for the load. Sizing the cooling to no more than 1.2x the load a the 1% outside design temp guarantees that then it's hot out it runs at least (1/1.2=) 83% of the time, and unlike just leaving the blower running it's actively cooling 83% of the time. It won't cool down the house as quickly as a 2x+ oversized system, but it will cool more evenly, and it will DRY the conditioned space air far better. To get a handle on the oversize factor, measure the duty cycle on afternoons when the temperatures are running near the 1% outside design temp (which is 87F in Cleveland.)

Similarly, limiting the furnace size to no more than 1.4x the heating load at the 99% outside design temp will guarantee a duty cycle of (1/1.4=) 71% when it's cold out, and more than 50% at the average wintertime temp. At 1.4x oversizing there is more than enough capacity to cover the Polar Vortex disturbance cold snaps, delivering the "warm summer breeze" at something like 90% of the time or higher, rather than the hot flash followed by the extended chill so characteristic of 3x oversizing (which a factor that gives hot air heating a bad reputation.)

Take a few clues in the videos & downloadable chapters on Home Comfort, and HVAC 101 (and HVAC 102) from Cleveland native Nate Adams, who has made a business out of fixing home comfort problems. Trying to fix it with just the HVAC or just the building envelope deficiencies usually doesn't work. The house and the HVAC are not independent systems. It's not usually cost effective on an energy use basis to swap out the oversized junk for right-sized equipment, but it's often necessary to hit comfort-nirvana.

The DIY tweaking I've recommended above working with the equipment you have is really in the realm of "low hanging fruit". but won't necessarily be wasted effort if you eventually bite the bullet on a bigger deal whole-house retrofit.

BTW: Most homes with basements leak tons of air at the foundation sill and band joist, and crazy amounts of heat out of the the foundation walls, even if not actively heating the house. Fixing the air leaks now is a good idea for humidity management, but DIY insulating the basement walls to the current IRC code minimum (=R15 continuous insulation) is "worth it" on both a wintertime comfort basis now, and fuel use basis if you're planning on staying there for more than 5 years. Using 3" of reclaimed roofing polyiso can be cheaper than a hybrid solution of 1" polyiso between the foundation and R13 studwall, and there are mulitple vendors of used foam in your area. It makes for a comfortable summertime DIY project, since you're hanging out in the cool basement rather than a hot attic. The not fully conditioned basement temps will be much more even year-round probably staying between 60-67F even on the coldest/hottest days in your area. (I've posted multiple detailed descriptions of best practices for basement & foundation insulation methods too. )

 

[Chris Redmond]

Honeywell has several models, this is the one I have. I bought it three years ago and it was $189. https://www.homedepot.com/p/Honeywell-Home-Wi-Fi-Smart-Thermostat-RTH9580WF/203926327. It is an excellent unit. Honeywell now has a T9 model (about a year old) that can be used with remote sensors and it can be programmed to which sensor to use for different times of the day and a person sensor. It is essentially a multi room thermostat. You read up on it on Honeywell site.

Most homes up north with forced air systems use the wall stud cavity as the cold air return or the grill is at the floor level. The floor plate is cut out all the way to the basement and sometimes the floor joist is covered in sheet metal to create a duct to get to the furnace. The supply side is always via duct work. If your returns on the second floor use the stud cavity, it is very easy to move the grills up on the wall near the ceiling (to pull the excess heat off), by opening up the drywall, move the grill and patching the drywall at the floor. It won't be perfect but it will help

Thanks Worth Florida. I did notice the wall stud cavity is used for the cold air return and the grill is at the floor level. We bought a Nest thermostat a few months ago, and so I'll have to see if it has some similar modes to what you describe in the Honeywell. Or maybe they have remote sensors too. If that doesn't end up suiting our needs, I'll definitely look further into the Honeywell you recommend.

 

[Chris Redmond]

Using exterior walls as a duct chase is in some ways worse than ducts in attics, since it creates a basement-to-attic (or near-attic) convection path. If the ducts are well sealed to the studs, sheathing and drywall at every floor boundary that can be mitigated, but it also means a gap in the wall insulation, and in winter that means the hottest air in the house (115F - 140F air in the supply duct) is in close proximity to the cold wall sheathing.




If it's the same air handler blower used for both heating and cooling it's a very durable component capable of a very high duty cycle- it's more likely that the heat exchanger in the furnace or the AC system will die of other causes before the blower fails. But there are other good reasons NOT to run the fan continuously such as:

* When the cooling cycle ends there is still moisture on the cooling coil that has been taken from the air. Running the fan puts that moisture back into the indoor air as the coil warms up between cooling cycles.

* No duct system is perfectly balanced or perfectly tight. When the air handler is running it generates pressure differences between rooms, and pressure differences between the rooms and "The Great Outdoors". A room that end up positively pressured to the outdoors when the air handler is running drives dry cooled air to the outdoors through every available local leak path, and rooms that are negatively pressurized relative to the outdoors suck in hot humid outdoor air when the air handler is running.

* A typical split capacity blower motor uses 600-1000 watts, which is the equivalent to running a 600-1000 watt space heater.

The sum total of these effects is a measurably increased net cooling load, and lower cooling efficiency.



Under the heading "other suggestions":

Start by improving the overall flow. If there are any doored off rooms in the house, but particularly rooms on the second floor that have supply registers but no return registers need to have retrofit return paths- a door cut at the threshold is not enough. I've posted multiple responses on this forum on how to make "jump duct" returns, as well as tips on duct sealing, sealing the duct boots to the wall/ceiling/floor etc., and how to measure the room to room pressure differences.

Tighten up the house to reduce the air handler driven parasitic loads. I've also posted a fair amount on [0]=31486']air sealing the house too.

To the extent possible, lower the cooling load to the second floor. Measure the ceiling temperature in several spots with a pistol grip IR thermometer (a $50-75 box store version is fine). If the difference between the ceiling temp and floor temp is more than 3F you're probably below the IRC prescriptive code-min R49 for climate zone 5 (which includes the northern half of OH), and may even be below the prior code-min R39. If you don't have at least 10" of insulation in the attic, add some, but do it right. (If you're going there I can lend a lot more detail, if you like.) No matter what, air sealing the attic floor/upper floor ceiling is a first and all-important step prior to adding insulation to the attic.

If the existing insulation is fiberglass (blown or batt) it's not doing nearly as much as it should for blocking heat from the attic. Fiberglass is somewhat translucent in the deep infra-red range, the heat that is being radiated from a hot roof deck, and the low density fiberglass in most attics is also not very air retardent. When the roof deck is hot the temperature of the fiberglass an inch from the top can even exceed the air temperature in the attic by a few degrees, which means you're insulating against a higher temp with an inch less insulation. And during the heating season convective loops between the cold attic and fiberglass cause it to underperform it's R value on the coldest nights of the year. Both of the IR and air retardency/convection issues can be significantly rectified by overtopping the with as little as 3" of blown cellulose, which is opaque to IR radiation, and even at 1.2-1.5lbs per cubic foot open-blown density is more than an order of magnitude more air retardent than an R19 batt.



Retrofit zoning by floor in a ducted air HVAC system can get complicated, but it's do-able. In most homes it's possible to run it as a single zone if the equipment is right-sized for the load, not so much if the systems are (all too commonly) 3x or more oversized for the load. Sizing the cooling to no more than 1.2x the load a the 1% outside design temp guarantees that then it's hot out it runs at least (1/1.2=) 83% of the time, and unlike just leaving the blower running it's actively cooling 83% of the time. It won't cool down the house as quickly as a 2x+ oversized system, but it will cool more evenly, and it will DRY the conditioned space air far better. To get a handle on the oversize factor, measure the duty cycle on afternoons when the temperatures are running near the 1% outside design temp (which is 87F in Cleveland.)

Similarly, limiting the furnace size to no more than 1.4x the heating load at the 99% outside design temp will guarantee a duty cycle of (1/1.4=) 71% when it's cold out, and more than 50% at the average wintertime temp. At 1.4x oversizing there is more than enough capacity to cover the Polar Vortex disturbance cold snaps, delivering the "warm summer breeze" at something like 90% of the time or higher, rather than the hot flash followed by the extended chill so characteristic of 3x oversizing (which a factor that gives hot air heating a bad reputation.)

Take a few clues in the videos & downloadable chapters on Home Comfort, and HVAC 101 (and HVAC 102) from Cleveland native Nate Adams, who has made a business out of fixing home comfort problems. Trying to fix it with just the HVAC or just the building envelope deficiencies usually doesn't work. The house and the HVAC are not independent systems. It's not usually cost effective on an energy use basis to swap out the oversized junk for right-sized equipment, but it's often necessary to hit comfort-nirvana.

The DIY tweaking I've recommended above working with the equipment you have is really in the realm of "low hanging fruit". but won't necessarily be wasted effort if you eventually bite the bullet on a bigger deal whole-house retrofit.

BTW: Most homes with basements leak tons of air at the foundation sill and band joist, and crazy amounts of heat out of the the foundation walls, even if not actively heating the house. Fixing the air leaks now is a good idea for humidity management, but DIY insulating the basement walls to the current IRC code minimum (=R15 continuous insulation) is "worth it" on both a wintertime comfort basis now, and fuel use basis if you're planning on staying there for more than 5 years. Using 3" of reclaimed roofing polyiso can be cheaper than a hybrid solution of 1" polyiso between the foundation and R13 studwall, and there are mulitple vendors of used foam in your area. It makes for a comfortable summertime DIY project, since you're hanging out in the cool basement rather than a hot attic. The not fully conditioned basement temps will be much more even year-round probably staying between 60-67F even on the coldest/hottest days in your area. (I've posted multiple detailed descriptions of best practices for basement & foundation insulation methods too. )

Thanks Dana. Wow, that is a wealth of information there. I've already actually done quite a bit of airsealing and insulating of the attic, rim joist and cantilevered floor based on some of your other posts. That took some time to figure out but the instructions were incredibly helpful since I hadn't done work like that before. Sounds like it's time for me to start learning HVAC now, so I appreciate the links, explanations, and the reference to a local business to boot.

One other thing I didn't mention initially is our house has many large east and west facing windows. Windows appear to be newer, but I doubt they have any advanced energy efficiency measures built in, at least from what I can tell. I started looking at window films, shades, and other treatments to help deflect heat in the summer and absorb it in the winter. Do you have any thoughts on strategies to deal with unwanted heat gain/loss through windows (other than buying new windows)? Or should that topic in general be bumped down the list, given the other ideas you already suggested which may pay bigger dividends and be more worth the time exploring? I don't think a whole house retro-fit is something happening anytime soon, so am interested in whatever interim techniques may give me the biggest bang for my buck in the meantime. Thanks again.

 

[Jadnashua]

Most homes have the supply and return ducts more optimized for heating than cooling. The hot air rises, so it is fairly common to have the ducts either in the floor or low on the walls. That tends to be good until you want to cool the place down. The cooler air is denser, so falls to the floor, so you end up with cold feet, and hot head...not the most comfortable situation. With the return ducts also often down low, in the cooling season, you're pulling the cooler air out of the room rather than the hotter air. It helps in the winter to pull that cooler air from low down. If your home happened to have primarily a cooling load, on those days when you may need heat, your head might be roasting, while your feet are cold.

So, there are some choices. One builder I saw ran all of his supply ducts to two outlets, one high and one low. As the seasons changed, you were supposed to close off the most suitable duct.

Personally, the air handler I chose has a multiple speed (16, I think) motor. I keep it on nearly all the time as unless it is actively cooling or heating, it runs on the lowest speed. This helps to keep the air moving and being filtered, too. It ramps up as heating or cooling is called for. In the cooling season, running the air by the evaporator slower initially means it can pull more humidity out of the air. It may never run at full speed unless you did a setback, or it's taking longer where it will ramp up, eventually, to maximum. At the end of the cycle, it slows down to extract any leftover heat or cold from the system before either shutting off, or returning to that really low setting. If you have that as an option for your furnace or heat exchanger, I highly recommend it. While many of the systems have the ability to change the fan speed, most of the time, it ends up being set for heating, which tends to be a slower setting than ideal for cooling. While heating, you don't want the fan running faster, since the wind chill effect can be a problem plus, the dwell time in the heat exchanger is shorter, the temperature rise isn't as great. FWIW, that air handler was installed around 1987, and has had the fan on most of those years. I did buy a spare motor, but have never needed to change it.

Anything that you leave on will add to your electric bill. A fan motor may be in the 1/2 HP range, or maybe slightly larger, depending. A 1/2 HP is under 400W, so if run 24-hours, is about 9.6KW. I haven't measured mine, but expect that on its lowest speed, it draws considerably less than that. From what is reported on my utility bill, I'm about average for my neighbors with the same type of unit.

I put a lot of insulation in my attic, way above the current minimum and it did make a difference. What also made a difference was adding a radiant barrier sheet on the bottom side of the roof rafters. There are roofing materials that can aid in reflecting some heat, with some metal roofs that can achieve over 90% reflection of IR. One of the newest asphalt roofing developments can reflect about 40% of the IR. These can help in the winter, too, since they tend to reflect heat lost to the attic back down, but lose any heat during the day that might have been gained through a normal roof. Given the winter sun is lower, and is up less time, your bigger gain is not losing as much outwards rather than what you might gain from solar influx.

 

[WorthFlorida]

Most newer air handlers have at least a two speed blower motor. In heat mode (electric elements) and fan on mode the speed is lower, cooling is the higher. The very high efficiency units with SEER ratings of 18 and higher the fan motor is an ECM, Electronic Control Motor, they are 240v motors with a built in AC to DC Voltage converter to drive the DC motor. Another lead is a signal lead with an voltage of 0-12 volts. This signal lead can control the fan motor to the RPM as programmed by the manufacture according to set temperatures, outside and inside temperatures. Static air pressure can also be factored. Unfortunately, these motors are two to three times more expensive than a standard blower motors. If one fails, you lost all monetary savings for a while with a HE unit.

 

[Dana]

One other thing I didn't mention initially is our house has many large east and west facing windows. Windows appear to be newer, but I doubt they have any advanced energy efficiency measures built in, at least from what I can tell. I started looking at window films, shades, and other treatments to help deflect heat in the summer and absorb it in the winter. Do you have any thoughts on strategies to deal with unwanted heat gain/loss through windows (other than buying new windows)?

East facing windows are giving the place a quick warm-up in the AM, but don't have a ton of heat gain after 10AM or so due to the oblique sun angle reflecting most of the incident light/heat. South facing windows have a surprisingly low gain during most of the cooling season due to the high sun angle reflecting a large fraction in summer (at the end of summer it starts to pick up rapidly though), but can be effectively shaded with awnings and overhangs.

The west facing windows are the worst, since it's a low sun angle, with the gain occurring after hours of the house baking in the sun pushing a peak cooling load later in the day, but before the outdoor temps have cooled significantly. Exterior operable shades or shutters are the best bet for killing the unwanted gain for west facing windows (or perhaps a tall maple or oak can be planted on the west side of the house? )

Any low-E window will cut solar gain compared to clear glass (single or double pane), some are better than others. A clear glass single pane has a solar heat gain coefficient (SHGC) north of 0.8 (80% of the heat/light passes through the glass), clear glass double panes run about 0.7. A low-E (single coated) window designed for heating dominated climates run about 0.4 (rejects more than half the heat), those designed for cooling dominated climates typically run in the mid- 0.2s (typically ~75% heat rejection.) To get it under 0.3 usually requires soft-coat sputtered silver as the low-E coating, under 0.2 usually requires both internal surfaces to have silver soft coat, which also cuts down on the visible light transmission (by quite a bit). A second low-E coating or a window film on the interior side can reduce the SHGC, but raises the peak temp of the sealed insulated glass. Double low-E glass without silver is available with an indium tin oxide hard-coat on the indoors surface (#4, in window-nerd speak) that hits the mid-0.20s without cutting the visible light dramatically the way even a single silver soft-coat does.

There are window films designed for use on low-E glass without raising the window temp high enough to blow the seal (not all window film is appropriate) but whether it would make enough of a difference to matter depends. If the SHGC of the glass is north of 0.4 (many windows designed for heating dominated climates are that high, some are even north of 0.6) Exterior shutters or exterior shades are more effective. There are many "see through" operable exterior shades that allow some light in, and some visibility- the room doesn't need to look like cave.

Translucent mirror-like reflective privacy shades on the interior can help too, since it reflects a portion of the incident light (including infrared) back out the window. Opaque but non-reflective shades not nearly much- the shade becomes the absorptive element of a convecting solar heater panel warming up the indoor air- cutting more light than heat. One way privacy window films are similar, but also cut a substantial amount of light, so an operable shade is preferable.

 

[Chris Redmond]

Most homes have the supply and return ducts more optimized for heating than cooling. The hot air rises, so it is fairly common to have the ducts either in the floor or low on the walls. That tends to be good until you want to cool the place down. The cooler air is denser, so falls to the floor, so you end up with cold feet, and hot head...not the most comfortable situation. With the return ducts also often down low, in the cooling season, you're pulling the cooler air out of the room rather than the hotter air. It helps in the winter to pull that cooler air from low down. If your home happened to have primarily a cooling load, on those days when you may need heat, your head might be roasting, while your feet are cold.

So, there are some choices. One builder I saw ran all of his supply ducts to two outlets, one high and one low. As the seasons changed, you were supposed to close off the most suitable duct.

Personally, the air handler I chose has a multiple speed (16, I think) motor. I keep it on nearly all the time as unless it is actively cooling or heating, it runs on the lowest speed. This helps to keep the air moving and being filtered, too. It ramps up as heating or cooling is called for. In the cooling season, running the air by the evaporator slower initially means it can pull more humidity out of the air. It may never run at full speed unless you did a setback, or it's taking longer where it will ramp up, eventually, to maximum. At the end of the cycle, it slows down to extract any leftover heat or cold from the system before either shutting off, or returning to that really low setting. If you have that as an option for your furnace or heat exchanger, I highly recommend it. While many of the systems have the ability to change the fan speed, most of the time, it ends up being set for heating, which tends to be a slower setting than ideal for cooling. While heating, you don't want the fan running faster, since the wind chill effect can be a problem plus, the dwell time in the heat exchanger is shorter, the temperature rise isn't as great. FWIW, that air handler was installed around 1987, and has had the fan on most of those years. I did buy a spare motor, but have never needed to change it.

Anything that you leave on will add to your electric bill. A fan motor may be in the 1/2 HP range, or maybe slightly larger, depending. A 1/2 HP is under 400W, so if run 24-hours, is about 9.6KW. I haven't measured mine, but expect that on its lowest speed, it draws considerably less than that. From what is reported on my utility bill, I'm about average for my neighbors with the same type of unit.

I put a lot of insulation in my attic, way above the current minimum and it did make a difference. What also made a difference was adding a radiant barrier sheet on the bottom side of the roof rafters. There are roofing materials that can aid in reflecting some heat, with some metal roofs that can achieve over 90% reflection of IR. One of the newest asphalt roofing developments can reflect about 40% of the IR. These can help in the winter, too, since they tend to reflect heat lost to the attic back down, but lose any heat during the day that might have been gained through a normal roof. Given the winter sun is lower, and is up less time, your bigger gain is not losing as much outwards rather than what you might gain from solar influx.

Thanks Jim.

Your recommendation for a furnace setting sounds interesting, let me see if I understand. If the blower has multiple speeds to choose from, and the ability to set different speeds for just the fan being on vs heating mode vs cooling mode, choose the lowest speed for the when just the fan is on, and if possible set a higher speed for cooling than for heating mode. Am I following correctly? Are you also saying these settings would help with pulling the humidity out of the air in the cooling season, or is that an additional setting on top of blower speed?

Also, very interesting to hear about the impact of a radiant barrier in the attic. I'll have to add that to the (growing) list of topics I need to research and learn more about.

 

[Dana]

Also, very interesting to hear about the impact of a radiant barrier in the attic. I'll have to add that to the (growing) list of topics I need to research and learn more about.

Unless you have way sub-code attic insulation (or IR-translucent insulation, such as low density fiberglass), with no ducts in the attic the effect of RB on peak and average cooling load will be de minimus. If you have a foot or more of (IR opaque) cellulose in the attic it's academic- measurable with instrumentation, but not consequential for the HVAC. In heating dominated climates RB in the attic (and high SRI "cool roof" shingles) adds more to the heating energy use than it saves in cooling energy- this should be your LAST resort.

Take several spot temperature readings of your upper floor ceilings on hot days, and compare it to the temperatures at the floor. An IR thermometer is a good tool for doing this quickly and frequently.

If you're the type who loves extra toys for playing with cell phones & tablet computers, the $200 FLIR is good for chasing down insulation gaps and other heat & air leaks in houses. The pro versions are more money, but not really "worth it" for chasing these problems. A $50-75 pistol grip IR thermometer can tell you almost as much, but can take an order of magnitude more time to figure it out. Both are useful tools to have though. I don't have the FLIR of my own to use at home, but I have access to a pro version at work, (used on problems where the higher resolution is actually useful, but completely unrelated to home performance.) At least one of the guys I work with has borrowed it from the lab to figure out stuff at his house. The ability to save the picture and scrutinize it later is useful.

 

[Jadnashua]

Based on the output of the HVAC system (BTU), and the mode you're running things, there will be some min/max air flow required to achieve a desirable air outlet temperature. That in combination with introducing a 'wind chill' effect, will help determine what fan speed works at any one time.

The faster the fan turns, the less change in temperature you'll achieve over the heat exchanger. Sort of like passing your hand over a candle flame. That also equates to the dwell time. In the winter, the fan speed should be set to achieve a good register outlet temp without blowing so fast that you are chilled by the wind speed. Conversely, in the summer, that cooling effect of the fan can be a bonus. But, that also means the air doesn't dwell as long to allow moisture to be extracted when passing through. The Trane unit I have always starts out slow. In the winter, this allows it to warm the ducts up prior to ramping up so you don't get that large initial burst of cold air and is also quieter. In the summer, it starts out slow as well, and passing by the evaporator coils more slowly allows the coils to cool off faster, and draw more moisture out of the air passing by. Once those initial timeouts have expired in either heating or cooling mode, the fan starts to step up. In milder weather, it may never get to full speed. At the end of the thermostat call, it ramps down, extracting some heat when in that mode, or cool.

At the time, Trane had an add where they had installed identical capacity systems in identical houses, one with their variable speed system, and one with the conventional fan...over the summer, the one with the variable speed fan extracted enough more moisture out of the air to fill a typical above ground pool.

My father's house used heat pumps. In the summer, the fan speeds were set for that optimum cooling. The house was downright uncomfortable in the winter when the system was on because it was not setup to lower the fan speed...the wind chill was cold depending on where you were sitting even though the actual air temperature was per the thermostat setting range. That higher fan speed also meant that the duct outlet temperature was too cold. The same amount of heat was being presented into the room, but with more air exchanges and lower inlet temperature.

FWIW, when I installed that radiant barrier in my attic, I had about the code minimum insulation there. I had already added insulation to my attic. The ceiling was noticeably hotter than the interior walls later in the afternoon and on into the evening. It immediately dropped the ceiling temperature when I finished. Later, I also added even more insulation. In the winter, my roof can still have snow on it for a week after everyone else in the condo townhouses has cleared, so it definitely made a difference. The condition of the roof shingles on my unit does not seem to differ from my immediate neighbors. If measured under lab conditions, y0u'd probably notice a difference.

If I had had my preference, when we reroofed the buildings, we would have gone with a metal, lifetime roof. A great heat barrier (a heat barrier of this type requires an air gap to be most efficient to minimize conduction) that would have helped with ice and helped everyone all year round with heating/cooling costs...but, it was a bit more expensive and was rejected by the board. Short term economy, but hey...we're getting close to needing to reroof again (been here a long time now!), and the total costs will end up being far more than it would have been had we gone with my original suggestion.

 

[Fitter30]

Any unit heatpump or straight ac 18*-24* temp drop across the evaporator coil. Above 24* coil freezes up below 18* will not pull enough humidity out of the air. Insulation helps but windows and doors can't be over looked. Two story house needs a second ac unit for the second floor why would you want to cool the second floor if nobody occupying it.

 

[Chris Redmond]

Unless you have way sub-code attic insulation (or IR-translucent insulation, such as low density fiberglass), with no ducts in the attic the effect of RB on peak and average cooling load will be de minimus. If you have a foot or more of (IR opaque) cellulose in the attic it's academic- measurable with instrumentation, but not consequential for the HVAC. In heating dominated climates RB in the attic (and high SRI "cool roof" shingles) adds more to the heating energy use than it saves in cooling energy- this should be your LAST resort.

Take several spot temperature readings of your upper floor ceilings on hot days, and compare it to the temperatures at the floor. An IR thermometer is a good tool for doing this quickly and frequently.

If you're the type who loves extra toys for playing with cell phones & tablet computers, the $200 FLIR is good for chasing down insulation gaps and other heat & air leaks in houses. The pro versions are more money, but not really "worth it" for chasing these problems. A $50-75 pistol grip IR thermometer can tell you almost as much, but can take an order of magnitude more time to figure it out. Both are useful tools to have though. I don't have the FLIR of my own to use at home, but I have access to a pro version at work, (used on problems where the higher resolution is actually useful, but completely unrelated to home performance.) At least one of the guys I work with has borrowed it from the lab to figure out stuff at his house. The ability to save the picture and scrutinize it later is useful.

Thanks Dana for this additional info on radiant barriers. I haven't read much on it before, so it's useful to understand the effect isn't as great as having something like cellulose in the attic, which is something we plan to do soon. We've got R19 fiberglass batt insulation up there now, and plan to add enough cellulose to get us to R55+ total (now that the things is as airsealed as I could get it). Also, the post on window treatments is helpful. Although, I may put in some of these other measures first, and see how that impacts the overall comfort level, before going further down the window path. I'm amazed at how interconnected airsealing, insulating and hvac are and how they affect so many different parts of the home. At least that's what I've gathered so far reading this and other posts. Appreciate all the great info!

 

[Dana]

We've got R19 fiberglass batt insulation up there now, and plan to add enough cellulose to get us to R55+ total (now that the things is as airsealed as I could get it).

An R19 batt is among the crummiest products still legal to sell as "insulation". It's density and air retardency is extremely low- more of an air-filter than an air-retarder. Without a top side air barrier it won't perform anywhere near it's rated R-value in either summer or winter. An R19 weighs the same as an R13, and when compressed to 3.5" in a 2x4 cavity performs at R13 (go figure!). The manufactured loft is about 6", but when compressed to 5.5" in a 2x6 framing bay it's performance is R18, assuming it has air barriers on all sides. Without a top side air barrier it's performance in an attic is abbysmal, but overtopping it with as little as 3" of cellulose (R11-ish) is sufficiently air retardent to bring the performance of that layer to the R18-R19 range again (for R30 total) more than doubling it's performance of a horizontal R19 without a topside air barrier at the temperature extremes. If you can get the total installed depth to ~15" with an overblow while maintaining a 1" air gap to the roof deck all the way out over the top plates of the exterior studwalls you'll be at the current IRC code minimums

If you can get the total installed depth to ~15" with an overblow while maintaining a 1" air gap to the roof deck all the way out over the top plates of the exterior studwalls you'll be at the current IRC code minimum. If it tapers down to something thin approaching the eaves on the roof slopes it may be worth doing some cut'n'cobbled foam along those edges to not lose too much overall performance. Heaping it to R55-R60 in the middle doesn't buy a whole lot if it's only R20 at the edges.

Are the joists 2x6, 2x8 or something bigger?

 

[Chris Redmond]

Based on the output of the HVAC system (BTU), and the mode you're running things, there will be some min/max air flow required to achieve a desirable air outlet temperature. That in combination with introducing a 'wind chill' effect, will help determine what fan speed works at any one time.

The faster the fan turns, the less change in temperature you'll achieve over the heat exchanger. Sort of like passing your hand over a candle flame. That also equates to the dwell time. In the winter, the fan speed should be set to achieve a good register outlet temp without blowing so fast that you are chilled by the wind speed. Conversely, in the summer, that cooling effect of the fan can be a bonus. But, that also means the air doesn't dwell as long to allow moisture to be extracted when passing through. The Trane unit I have always starts out slow. In the winter, this allows it to warm the ducts up prior to ramping up so you don't get that large initial burst of cold air and is also quieter. In the summer, it starts out slow as well, and passing by the evaporator coils more slowly allows the coils to cool off faster, and draw more moisture out of the air passing by. Once those initial timeouts have expired in either heating or cooling mode, the fan starts to step up. In milder weather, it may never get to full speed. At the end of the thermostat call, it ramps down, extracting some heat when in that mode, or cool.

At the time, Trane had an add where they had installed identical capacity systems in identical houses, one with their variable speed system, and one with the conventional fan...over the summer, the one with the variable speed fan extracted enough more moisture out of the air to fill a typical above ground pool.

My father's house used heat pumps. In the summer, the fan speeds were set for that optimum cooling. The house was downright uncomfortable in the winter when the system was on because it was not setup to lower the fan speed...the wind chill was cold depending on where you were sitting even though the actual air temperature was per the thermostat setting range. That higher fan speed also meant that the duct outlet temperature was too cold. The same amount of heat was being presented into the room, but with more air exchanges and lower inlet temperature.

FWIW, when I installed that radiant barrier in my attic, I had about the code minimum insulation there. I had already added insulation to my attic. The ceiling was noticeably hotter than the interior walls later in the afternoon and on into the evening. It immediately dropped the ceiling temperature when I finished. Later, I also added even more insulation. In the winter, my roof can still have snow on it for a week after everyone else in the condo townhouses has cleared, so it definitely made a difference. The condition of the roof shingles on my unit does not seem to differ from my immediate neighbors. If measured under lab conditions, y0u'd probably notice a difference.

If I had had my preference, when we reroofed the buildings, we would have gone with a metal, lifetime roof. A great heat barrier (a heat barrier of this type requires an air gap to be most efficient to minimize conduction) that would have helped with ice and helped everyone all year round with heating/cooling costs...but, it was a bit more expensive and was rejected by the board. Short term economy, but hey...we're getting close to needing to reroof again (been here a long time now!), and the total costs will end up being far more than it would have been had we gone with my original suggestion.

There is a fan setting on our furnace/air handler but it's part of the wiring schematic that I'm hesitant to change until I read more about how to do without damaging the unit. We may just wait until an upcoming annual inspection of our furnace to get the technician's guidance on how change to fan speed. Our furnace is a high efficiency unit that is fairly new. We didn't purchase the furnace, since we just moved into our home a year ago. I'm interested to know if we have ramp up/cool down features like you describe with the way the fan speed is controlled too. The fact that a slower fan can extract enough water in one summer to fill a pool is incredible to think about, but believable given how quickly my small dehumidifier fills up in the basement.

The metal roof concept is interesting. We're a long ways off from replacing our roof (I hope!), but when the time comes, I would want that option on the table. I don't know enough about those yet though to have a fully formed thought one way or the other.

 

[Chris Redmond]

An R19 batt is among the crummiest products still legal to sell as "insulation". It's density and air retardency is extremely low- more of an air-filter than an air-retarder. Without a top side air barrier it won't perform anywhere near it's rated R-value in either summer or winter. An R19 weighs the same as an R13, and when compressed to 3.5" in a 2x4 cavity performs at R13 (go figure!). The manufactured loft is about 6", but when compressed to 5.5" in a 2x6 framing bay it's performance is R18, assuming it has air barriers on all sides. Without a top side air barrier it's performance in an attic is abbysmal, but overtopping it with as little as 3" of cellulose (R11-ish) is sufficiently air retardent to bring the performance of that layer to the R18-R19 range again (for R30 total) more than doubling it's performance of a horizontal R19 without a topside air barrier at the temperature extremes. If you can get the total installed depth to ~15" with an overblow while maintaining a 1" air gap to the roof deck all the way out over the top plates of the exterior studwalls you'll be at the current IRC code minimums

If you can get the total installed depth to ~15" with an overblow while maintaining a 1" air gap to the roof deck all the way out over the top plates of the exterior studwalls you'll be at the current IRC code minimum. If it tapers down to something thin approaching the eaves on the roof slopes it may be worth doing some cut'n'cobbled foam along those edges to not lose too much overall performance. Heaping it to R55-R60 in the middle doesn't buy a whole lot if it's only R20 at the edges.

Are the joists 2x6, 2x8 or something bigger?

I've read some other posts on how poor fiberglass batts perform, and I'm guessing ours are on the lower end of even that low end of the spectrum. I had to pull up every batt when airsealing, and spent weeks shuffling them around up there resulting in some compression. I did my best to tape up any tears in the kraft facing with temp rated foil tape, and reinstalled as best as I could, but they look pretty crummy.

The joists are 2x6. The slope of the roof is pretty low. I airsealed the top plates, but had to use the xl spray (4'?) foam gun to even be able to get back there. I also installed accuvent baffles (with extensions towards the ridge vent). I think the baffles have a 1.5" clearance from the roof deck. Attached is a photo. There is an orange mark on the rafter where 18" height would be (12.5" above the top of the 2x6 joist). It's a marker for the height to which I planned to add blown-in cellulose. It may be hard to see, but the batt is basically touching the baffle above the top plate. Where and how are you suggesting the cobbled foam be installed? Could the cellulose be dense packed above the batts at the top plate somehow?

Every time I walk by a house now that has a steep roof, I think about how lucky that homeowner is, lol. I guess weeks on end spent in an attic will do that to a p erson.

 

[Dana]

I've read some other posts on how poor fiberglass batts perform, and I'm guessing ours are on the lower end of even that low end of the spectrum. I had to pull up every batt when airsealing, and spent weeks shuffling them around up there resulting in some compression. I did my best to tape up any tears in the kraft facing with temp rated foil tape, and reinstalled as best as I could, but they look pretty crummy.

When fitted well, with no compressions, voids, or gaps, mid or high density batts do OK. High density "cathedral ceiling" type batts do well (thermally) even without air barriers on all six sides.

^^It looks like the low density R19s got ripped up and compressed a bit during the air-sealing phase.^^

A well-installed attic batt will be tucked in at the edges to ensure contact with the ceiling gypsum below, then teased/tugged out so that the top surface is fairly flat and smooth. Some of those compression spots look like there is less than 3" between the top of the batt and the ceiling gypsum, which is about R9-R10, and passes twice or more the heat rate of a square foot of perfectly fitted R19.

Repairing the rips in the kraft facers was an unnecessary step. It's impossible to use batt facers as an air barrier for the ceiling, but they are still pretty reasonable "smart" vapor retarders even with rips, since vapor diffusion is all about total surface area, not air tightness. Air sealing should be performed on the ceiling layer (from the attic side). If you are going to blow cellulose over it, don't bother re-re-installing the batts- just smooth out the torn lumps using a lawn rake or something to where they're not sticking up much higher than the joist tops.

The joists are 2x6. The slope of the roof is pretty low. I airsealed the top plates, but had to use the xl spray (4'?) foam gun to even be able to get back there. I also installed accuvent baffles (with extensions towards the ridge vent). I think the baffles have a 1.5" clearance from the roof deck. Attached is a photo. There is an orange mark on the rafter where 18" height would be (12.5" above the top of the 2x6 joist). It's a marker for the height to which I planned to add blown-in cellulose. It may be hard to see, but the batt is basically touching the baffle above the top plate. Where and how are you suggesting the cobbled foam be installed? Could the cellulose be dense packed above the batts at the top plate somehow?

Dense packing isn't really an option here, and won't give you much benefit. At higher density cellulose is more air retardent, but doesn't have appreciably higher R/inch. Even 1.2- 1.5lbs open blown cellulose is air retardent enough, and runs R3.5-R3.7/inch.

If the top of the batt is touching the baffle you have about 6"of height to work with over the top plate? Stacking in 6" of cut'n'cobbled polyiso would bring that up to R36, which is pretty good. At 8" polyiso would pretty much meet the full code-min. Whether it's "worth it" to put in the time & effort for that much cut'n'cobble is up to you- it depends on your performance goals. Laying in 4" of polyiso directly on top of the top plate and filling in the remaining 2" with cellulose would be R30, which is pretty effective in the cooling season (more than twice the performance of poorly installed R19 batts), and still decent enough in the heating season. It's pretty easy to rip a bunch of foam board into 14" wide x 2' long strips and foam them in place, and just blow over them.

A common way to get to nearly-code min or better while keeping a storage deck or catwalk in my area is to install another set of 2x6 or 2x8 perpendicular to the existing ceiling joists, and fill it to the joist tops with cellulose. That would be 11' of fluff (~R40-ish) at center cavity, but since there would be 5.5" (R20-ish) of cellulose over the tops of the original joists and a similar amount fluff (fiberglass + cellulose) under the bottoms of the secondary perpendicular joists the thermal bridging of the framing is dramatically reduced, and the assembly meets code in on a U-factor basis. To meet code-R on an R-value basis, use 2x8s, which would give 12.75" of depth, which at R3.7/inch would be R47-ish (close 'nuff to never have to show the math on the thermal bridging.)

 

[Chris Redmond]

When fitted well, with no compressions, voids, or gaps, mid or high density batts do OK. High density "cathedral ceiling" type batts do well (thermally) even without air barriers on all six sides.

^^It looks like the low density R19s got ripped up and compressed a bit during the air-sealing phase.^^

A well-installed attic batt will be tucked in at the edges to ensure contact with the ceiling gypsum below, then teased/tugged out so that the top surface is fairly flat and smooth. Some of those compression spots look like there is less than 3" between the top of the batt and the ceiling gypsum, which is about R9-R10, and passes twice or more the heat rate of a square foot of perfectly fitted R19.

Repairing the rips in the kraft facers was an unnecessary step. It's impossible to use batt facers as an air barrier for the ceiling, but they are still pretty reasonable "smart" vapor retarders even with rips, since vapor diffusion is all about total surface area, not air tightness. Air sealing should be performed on the ceiling layer (from the attic side). If you are going to blow cellulose over it, don't bother re-re-installing the batts- just smooth out the torn lumps using a lawn rake or something to where they're not sticking up much higher than the joist tops.




Dense packing isn't really an option here, and won't give you much benefit. At higher density cellulose is more air retardent, but doesn't have appreciably higher R/inch. Even 1.2- 1.5lbs open blown cellulose is air retardent enough, and runs R3.5-R3.7/inch.

If the top of the batt is touching the baffle you have about 6"of height to work with over the top plate? Stacking in 6" of cut'n'cobbled polyiso would bring that up to R36, which is pretty good. At 8" polyiso would pretty much meet the full code-min. Whether it's "worth it" to put in the time & effort for that much cut'n'cobble is up to you- it depends on your performance goals. Laying in 4" of polyiso directly on top of the top plate and filling in the remaining 2" with cellulose would be R30, which is pretty effective in the cooling season (more than twice the performance of poorly installed R19 batts), and still decent enough in the heating season. It's pretty easy to rip a bunch of foam board into 14" wide x 2' long strips and foam them in place, and just blow over them.

A common way to get to nearly-code min or better while keeping a storage deck or catwalk in my area is to install another set of 2x6 or 2x8 perpendicular to the existing ceiling joists, and fill it to the joist tops with cellulose. That would be 11' of fluff (~R40-ish) at center cavity, but since there would be 5.5" (R20-ish) of cellulose over the tops of the original joists and a similar amount fluff (fiberglass + cellulose) under the bottoms of the secondary perpendicular joists the thermal bridging of the framing is dramatically reduced, and the assembly meets code in on a U-factor basis. To meet code-R on an R-value basis, use 2x8s, which would give 12.75" of depth, which at R3.7/inch would be R47-ish (close 'nuff to never have to show the math on the thermal bridging.)

Looking back on the airsealing I did to the top plates, I now wish I had taken the polyiso approach from the start. Since I had to use a long foam gun to seal the top plate, there is a large amount of foam on the top of each top plate right now. I erred on the side of overkill, since I couldn't quite see if I was getting the foam into the seam. I'll have to think about if it's worth it to go back now to cut all that foam to be flush with the plate and then add stacked polyiso and refoam, or just wait for now, since a few other outdoor projects I'm working on are more attractive now that it's summer and the attic is heating up.

I really appreciate all the great information, you've given me a lot to think about!