DIY Zoning

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Tom466

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Hi,

I currently have a a forced air system in a two story home and have the common problem with the difference of temperatures on each floor. Therefore I am looking into separating the floors into zones. Through research on the web I found several systems that are available to do this using dampers. One system in particular that comes with good reviews is Honeywell. My issue is that the majority of the ductwork coming from the furnace is behind wallboard. Also, from what I can tell the main trunks coming from the furnace feed both top and bottom floor vents. ( not one side is top floor and other side is bottom floor). Based on what I have seen it seems that my only option is using bladder type dampers at each vent (16 total) unless I open walls and ceilings? Just wondering if anyone can provide any experience/help with this.
Thank you!
 

Tom Sawyer

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Be prepared to spend more money than it's worth. Zoning forced warm air is not easy because you have to do something about the lost CFM when only one zone is open. You need a bypass and balancing. You're better off to adjust airflow to individual registers to achieve an overall temperature balance throughout the house.
 

Tom466

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Be prepared to spend more money than it's worth. Zoning forced warm air is not easy because you have to do something about the lost CFM when only one zone is open. You need a bypass and balancing. You're better off to adjust airflow to individual registers to achieve an overall temperature balance throughout the house.

Thank you so much for your reply.
So, if I understand you correctly you don't recommend installing zoning dampers?
Just try to adjust the temperature by manually opening/closing the registers on each floor?
 

Jadnashua

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I have no association with these guys, but am interested in maybe making the plunge with their equipment
http://www.keenhome.io/

It might solve some of your issues, but they're not inexpensive. I'd have made the plunge, but my upstairs uses round ceiling vents, and they are now only making a limited selection of rectangular ones. I might end up putting in a round-rectangular adapter, but don't look forward to messing with the ceiling with lots of blown in cellulose up there and no easy access.
 

Tom Sawyer

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The problem with those is that the heat exchanger is designed to work with a certain CFM airflow across it and when you restrict openings or returns, it changes airflow which causes short cycling and increased noise. Well zoned systems have a bypass that keeps airflow across the exchanger constant.
 

Jadnashua

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FWIW, they do have a pressure sensor in each one so they'll assess whether they can be closed or only partially closed to keep the air flowing (supposedly) well, and, they network with each other so they know what the others are doing in your house. Over time, they'll learn where they need to be to get the rooms at the thermostat setting, without overheating one, and under heating others.

It will be interesting to see how well they work out. THey just started to ship this fall after about a year of design of both the registers and the software to control them.
 

Tom466

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First off, thank you Tom and jadnashua for all your input on this subject, I really appreciate your professional opinion.
I have seen a couple different solutions to adding "automatic vents" to your HVAC system. I believe there is also another startup company out there as well, but they have not started shipping yet. If I find them again on the web I'll be sure to post a link.
As jadnashua said, what makes the Keen Home system interesting are the built in pressure sensors. They have an "Analyze My Home" feature in their app which I downloaded and tried. To my surprise the app recommended I purchase 2 Smart Vents for comfort or 13 for efficiency. But, according to their website the maximum number of Smart Vents you can install on a system is 8. I have no idea how only 2 vents will help for comfort. My downstairs is normally comfortable since that is where the thermostat is located, but the upstairs will typically be at a 3 to 7 degree difference and
each level has 8 vents.
 

Jadnashua

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Because the registers literally communicate with each other, they can tell if one area is colder than another, and shut down some heat (or cooling) delivery to some registers while then forcing more conditioned air to the others to help balance things out. With their pressure sensors, they understand when they've shut down 'too much', and will adjust to keep the air flow at a safe rate. As I said, though, half of my registers are round, and they do not make a round one (yet?), and I'm not keen on converting them to rectangular. It's sort of like having automated dampers in each duct to help balance things out. Note, while 'fixed' ones may help, things like solar heating or wind could change that on an hour-to-hour or day-to-day basis, and having them adjust on their own should help. Course, they use batteries, and while they say they last 2-3 years, when the time comes, that's a LOT of batteries to replace!
 

Tom466

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Thanks Steve.
I seen that video as well a while back and if I remember correctly it's not DIY and in my area would probably run somewhere around 7k.
As promised I found the other DIY vent controlled system that is not shipping yet but taking orders.
Here is the link: https://www.ecoventsystems.com
It does not seem to be as "smart" as the Keen system which monitors the air pressure and cost looks to be around 2k for my home. (Almost double the cost of Keen)
 

Dana

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Smart vents that shut down completely can create problems with the total flow requirements at the air handler, and aren't a great solution. They don't save energy either- they unbalance the system which creates higher air-handler driven outdoor air infiltration (well documented by the folks at the Lawrence Berkeley National Laboratory in multiple in-situ and lab studies.) Closing off registers to unused rooms similarly raises rather than saves energy use.

You're better off hand-tweaking the temperature balance with operable vanes than attempting to zone it (or micro-zone it with smart registers that can close completely.) Of course, in two-story houses with heating & cooling sharing the same ducts the flows that balance temps well during the heating season will be different from those during the cooling season.

Tom has it right, zoning air delivery in a way that doesn't use more energy or put the equipment at risk is almost always more trouble (and money) than it's worth. Spending the money instead on upgrading the air-sealing & insulation levels of the house is a better investment in both comfort and efficiency.
 

Dana

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That article refers to a blog run by Allison Bailes, Phd.

Allison knows a lot more about the nature of the problem than the business school marketing geniuses behind Keen, who re-invented the same broken wheel, only with microprocessor control this time. (This is despite Allison's being encumbered with a Phd in physics. ;) )

They claim to have "solved" the problem by limiting the pressure at any register to 1.2 inches of water, but I'm less than convinced that 1.2 iwc is a magic number that works for all systems (or even ANY system). Air handlers are typically specified for flow at 0.5-0.75 iwc- the system could already be incurring trouble by the time the first smart vent detected 1.2 iwc at the register.
 

Poncho

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Yeh....Zone dampers...who needs 'em. When I Zoned me 2 new BR's back in '03 I asked Steve the owner of the new install jus how well them there hot dog Dampers gonna work, he tilted his head towards me'till his glasses slid down an parked on his nose, said drolly "well Mike, anytime you gots mechanical stuff derr be Dragons". Took 15 years but the Dragons are damp'n me dampers. When my BR heat kicks in shoots to BOTH rooms, when lil woman heat kicks in it does what it is supposed. Heat her room only. Haven't eyeballed the Zone Brain yet but was wondr'n if anyone can sling me a clue. Thanky in advance.
 

Jorgebaloy

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Let’s say you live in a two-story home without any zoning. During the summer, it’s always nice and cool downstairs. That’s where the thermostat is, so you can feel confident that the ambient temperature will match what’s on your thermostat.

Upstairs… not so much.

Thanks to the reverse stack effect – not to mention warmer air rising from your downstairs living room to your upstairs bedrooms – upstairs temperatures can be 3 to 7 degrees warmer than the number on your thermostat. If you want the temperature in your bedroom to be 75 degrees at night, you might have to lower your thermostat to 68 degrees!

To fix the problem, you decide to add two zones to your existing system, one for upstairs and one for downstairs. But you’re using a “standard,” single-stage air conditioner with a single-speed blower. It’s the kind that either runs at full blast or not at all. Given your equipment, here are some things to keep in mind before moving forward:

Installing dampers inside your ducts is the most common way to add zones to an existing system. However, your blower can only operate at 100% capacity. The static pressure will be too intense for just the ductwork associated with a single zone (50% or so of your total ductwork). You’ll need a way to redirect the excess air.

To deal with the excess air produced by your HVAC equipment, you’ll probably need a bypass duct that connects your supply air to your return plenum. The zone calling for air will receive sufficient cooling for the associated space, and any excess air will enter the bypass duct.

Now you’re sending cool air back into the return, which makes your evaporator coil get colder. A colder evaporator coil is a less efficient evaporator coil.

Even when you’re cooling your entire house, the bypass duct will siphon air from the supply. You’ll make your air handler work harder.
 
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