Home Heating Tips to Save Money?

Discussion in 'Tankless Water Heater Forum' started by Robenco15, Mar 12, 2018.

  1. Robenco15

    Robenco15 New Member

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    Got the tank in July. Brand new, two tanks filled. I don’t remember what that cost, but the above October fill was the very first fill since acquiring the tanks.

    Why? I’m concerned about heating my home at 125f supply, hot water has always been good and cheap.
     
  2. Ladiesman217

    Ladiesman217 Member

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    Just calculating cost to heat hot water. Seems to be about 15 gallons of propane per month, or 1/2 gallon per day.
     
  3. Ladiesman217

    Ladiesman217 Member

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    What pipes froze in January?

    Heating zone pipe? Water distribution pipe? Pipe burst as a result, or just a temporary freeze?
     
  4. Dana

    Dana In the trades

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    The only ways know if 125F water is going to be enough to heat the kitchen and living room is to do a careful room by room heat load calculation & compare the baseboard lenghts in those rooms to the load, or empirically, by trying it. We DO know that you don't have enough to heat the whole house with 125F water when it's 9F out- we've done the basic math.

    At +9F (56 F below the presumptive 65F heating cooling balance point) the baseboard would have to deliver about 317 BTU per running foot, which takes 140F water, from my previous post. But it's not 9F outside these days, so the water doesn't need to be that hot (right now), since the heat load load less at recent days' temperatures than it is at 9F.

    At 125F you'll get an AWT of about 120F, and the baseboard will be delivering about 200 BTU/hr per foot of baseboard. For the whole 144' of baseboard that's 28,800 BTU/hr. Your linear load constant previously calculated is 815 BTU/degree-hour, so 28,800 BTU/hr will cover your load down to 28,800/815= 35F cooler than 65F, or about 30F outdoors. When it's colder than 30F the water temp will have to be a bit higher than that.

    But 30F is a few degrees cooler than the mean outdoor temp for January in Norwalk, in an average year. With outdoor reset control raising and lowering the water temperature automatically in response to outdoor temperature the system can operate in the condensing zone nearly ALL the time, only rising above the condensing zone during cold snaps and during the overnight hours of a few weeks in January, pretty much, more or less.

    Run a room by room I=B=R type heat load calculation on the kitchen & living room zone, and specify how much baseboard there is on each room. (Go ahead and make a spreadsheet for all the rooms in the house, if you like.) We can make adjustments for the 24/7 plug loads like refrigerators and for warm human bodies to fine tune it, but just the basic I=B=R conducted load will ballpark it pretty well.

    Frozen pipes are an indication of either air leakage (likely) or insufficient basement or wall insulation. Air sealing is job #1 , followed by insulation. For framed walls dense packing cellulose to ~3.5lbs per cubic foot density or blown fiberglass to ~1.8lbs does a pretty good job of plugging air leaks with fiber, but the band-joists & foundation sill in the basement is often the largest non-obvious air leak in many/most houses. With more information on the foundation & construction type I can offer guidance on dealing with this stuff.
     
  5. Robenco15

    Robenco15 New Member

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    Frozen pipes were the cold water pipes to the 1st floor exterior wall bathrooms. Also as a result our baseboards weren’t getting any cold water to heat through the Navien. It was a few days in a row of a wind chill below zero and us not realizing that it could happen (first winter with home).

    Nothing burst though and some space heaters did their job to defrost them.
     
  6. Dana

    Dana In the trades

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    Potable water should not be running through the baseboards! In almost every state that would be a code violation, though it's often allowed if the total length of plumbing in the heating loop is very short (way shorter than 144' + distribution plumbing.) In MA it's only allowed if all zones are operated at some minimum duty cycle (even in summer) to prevent stagnation in the plumbing. If you look at page 75 of the installation manual you'll see that the potable water is isolated from the heating system water by a plate type heat exchanger (item #65 in the diagram.) If it's been plumbed differently that should be corrected! Can you take some pictures of the near boiler plumbing and post it here?

    Wind chill has nothing to do with when water in pipes freezes. Wind chill is only about the rate heat is lost from exposed human skin.

    Are the pipes that froze inside the exterior wall (almost always a bad idea in New England)? If yes, insulating those wall cavities may require opening up the wall where the pipes are and putting rigid foam insulation between the plumbing & exterior sheathing, and blocking any blown insulation from filling in between the pipe an the interior side. That way the pipes stay completely within the thermal boundary of the house.

    Setting up the outdoor temperature sensor and reset curves ("K-factor" in Navien's documentation) is covered starting on p47 of the manual. There are DIP switch settings relate to the control modes. Setting position 4 on switch 8 modulates the burner control the return water temperature rather than the supply temperature, and that's more relevant to the condensing efficiency than the supply temperature. Looking at page 48, the rough heat load and baseboard estimates, it looks like when in return temperature control mode, the ideal K-factor would be somewhere between 2 and 3. If set up in supply temperature control mode the K-factor that works best will probably be somewhere between 1 & 2. In either mode the lowest setting that actually heats the place would yield the highest efficiency.
     
  7. Ladiesman217

    Ladiesman217 Member

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    I assume that the heating zone pipes froze as well as the bathroom cold water pipes froze. The heating system water is isolated from the main water supply by a check valve. The heating system water is a closed system.

    I note that the first floor's two bathrooms and the bedroom are on one heating zone. What specific temperature settings did you use for the thermostat for that zone? Single temperature setting?

    Do you have automatic set back thermostats installed, or are they the old manual thermostats?

    My water pipes froze one time years ago. In the basement, the outside wall kitchen/vent pipe had a draft from the attic that hit the nearby water pipes. The pipe split in my case. I sealed the openings around the vent pipe and that cured that draft problem.
     
  8. Robenco15

    Robenco15 New Member

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    Like I said. I’m not totally sure what I’m talking about. I’m sure it was installed correctly.

    Also, the basement insulation would be at the rim joists. Still not worth only doing the rim joists? $1500 for rim joists. $5100 for first floor exterior walls. Can probably swing the basement insulation.
     

    Attached Files:

  9. Robenco15

    Robenco15 New Member

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    Also, is there any chance keeping it at 125f and my thermostat basically around 65f the entire time is burning through propane even quicker? As opposed to having it at 180F and turning the thermostat up and down between when I’m home (and not sleeping) vs. not home.

    They filled my tanks 10 days ago. They are already down to around 50% from 80%.

    I’m at a loss. I can’t afford $600 a month heating bills.
     
  10. Dana

    Dana In the trades

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    The basement's foundation sill and band joist is usually a significantly bigger air leak than all the window & door crackage in the house combined. That leak is also near the bottom of the "stack effect" stack, making it far more important than air leaks at mid-level in the house. It's DEFINITELY worth air sealing and insulating the band joist with an inch or two of closed cell foam covered over by R15 rock wool batts trimmed to fit without gaps or compressions.

    Of course the rest of the basement wall (particularly the above grade portion) is also well worth insulating.

    Setting back the thermostat saves AT MOST about 5% of the energy if the boiler is at a single efficiency. Running it in condensing mode with entering water at the boiler under 120F almost always saves more than that. Try it.
     
  11. Robenco15

    Robenco15 New Member

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    Ok great. Thank you.

    How do I go about setting the water temperature that enters the boiler? I can't figure that out. It isn't around 125F since the supply is set to 125F?

    How do I know if it is in condensing mode? Is that the same as money saving mode (that gives me an icon on the screen).
     
  12. Dana

    Dana In the trades

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    Read the manual. Make it your bedtime story for a week See page 51. This boiler can be set to modulate the firing rate up and down in response to the entering water temperature rather than output temperature. Without the outdoor sensor you can still set it up to control the return water to 95F, 110F, 125F ,or 140F with the DIP switches. At 140F there is effectively zero condensing efficiency, but at 11oF entering water temperature the raw combustion efficiency will be in the mid 90s (as oppposed to mid-80s if blasting away at 180F out.)

    Try running it at 110F return water temp, see if it keeps up with the load (it might, it might not.) If it doesn't keep up, set it to 125F- it probably will manage the load at recent If it keeps up and isn't short-cycling, leave it there, but order the outdoor reset sensor (and the pre-made sensor wire with the connector).

    It's not big money, and will enable the system to run in condensing mode most of the time, only increasing the temperature as-needed when the outdoor temperatures drop.

    Even though it only tests in the low 90s on a AFUE test, it's combustion efficiency will be higher than the AFUE efficiency with 110F return water, and most of the time that's likely to still work, without short-cycling the boiler. Tuning the reset curve (K-factor) will take a bit of experimentation to dial it in perfectly, but it's worth it for both efficiency & comfort. As you fix up the insulation & air sealing issues you'll be able to drop the temperatures even lower, for even higher efficiency.

    A typical natural gas boiler condensing curve looks like this:

    [​IMG]

    It's actually more complicated than that, since it's also a function of the firing rate- less efficient at the max firing rate than at the minimum at every point on the curve:

    [​IMG]


    Propane has more water in the exhaust than natural gas, and starts condensing a slightly higher temperature than natural gas, so the efficiency curve is slightly higher natural gas at any point on the curve. So with 110F return water at minimum fire it'll most propane boilers will ~95% efficiency or even a bit higher, whereas natural gas will usually be a bit shy of that mark (as seen in the first picture.)
     
  13. Robenco15

    Robenco15 New Member

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    Thanks. Taking a look at the dip switches in my pictures above, it doesn't look like it matches anything from the manual. The 8 switch dip switch has 3, 6, and 7 on. The manual says for 125F would have 4 and 6 on. For the supply temperature, none of the options match what is on the 8 switch dip switch either.

    Can you make sense of that? I'm hesitant to just start switching things on and off without really knowing what I'm doing.

    I don't have to ability to change the return temperature settings, or the k curve, or anything but the supply temperature with the remote control.

    Edit: Ok, it looks like 3, 6, and 7 means I have the return temp. at 125F and the 7 being on refers to the 120F DHW.

    You mention being able to handle the load or whatever at 110F. How would I know if it is working or needs to be set to 125F?
     
    Last edited: Mar 20, 2018
  14. Dana

    Dana In the trades

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    Raising the water temperature increases the rate at which heat is being emitted by the baseboard, lowering the water temperature lowers the rate. You'll know if it's "working" from a practical point of view if the house doesn't get cold overnight. If it's not a high enough water temperature the house will be uncomfortably cold in the AM rather than than near the thermostat's setting.

    In order for it to be controlling based on return water temperature, SW2 position #4 needs to be ON. See page 58.

    In the picture position #4 is off, which puts it under supply temperature control, not return control. With #5 off, #6 on it's controlling the supply output temperature to 160F.

    With #4 on and...

    ...#5 off, #6 on it would be controlling to an entering water temperature of 125F...

    ...#5 on, #6 off it would controlling to an entering water temperature of 110F.

    So, flip #4 & #5 on, and #6 off, see how it does. If it's not maintaining room temperatures overnight, leave #4 on, but flip #5 off, and # 6 on, see if that's enough.

    How much of this can be over-ridden and adjusted by the remote controller isn't immediately obvious. That's probably all covered in the user manual, which should become your OTHER bedtime reading for awhile.

    As you get into it and install the outdoor temperature sensor you'll probably find this thread useful.

    If you don't have printed copies of the installation and user manuals, it's a idea to download and archive them (or even print them and keep them in a protected binder near the boiler.)
     
  15. Robenco15

    Robenco15 New Member

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    Thanks Dana, so I'm going to go home and make those adjustments.

    I have read through some of the user manual. I don't seem to be able to do any of the options on the remote control other than adjust the DHW water temp. and the supply temp. (which I have had down to 125F for about a week now). Maybe flipping those switches like you said above will make more things available to me.

    Here is the response I got from the insulation company after I contacted them today about possibly just doing the basement -

    "When I came out to your home I suggested installing 2 inches of closed cell spray foam in your basement perimeter rim joist. The rim joist is an area of the house that receives a large amount of cold air infiltration. This cold air infiltration enters your home due to a “stack effect” . The stack effect happens when you lose heat from your attic, this rising air needs to be replaced and will actually pull cold air through the rim joist. By installing closed cell spray foam you will be creating an air barrier around the rim joist, this greatly reduces the amount of cold air infiltration created by the stack effect.

    I suggested doing both the rim joist and the exterior walls to be done at the same time do to the fact you have little to no insulation in the exterior walls. By sealing the rim joist you will be slowing down air coming into you upper floors from the basement but still left vulnerable from the cold air entering from the exterior walls. I would recommend doing both options still but understand about budgets, so if you would like to do the rim joist first and save the walls it would still be a good option. I would definitely recommend doing the walls at some point because they are in need of insulation."

    Sounds a bit different than when I was told it would basically make no sense to just do the basement. Hopefully doing that insulation at the rim joists will be enough to warm my home up. Between that and these changes with my Navien, hopefully next winter will be better.
     
  16. Dana

    Dana In the trades

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    Just the rim joist will do something, but empty stud bays are just individual flues/stacks with a lot o' suck, in addition to their low-R and direct air leakage. Filling the stud bays with cellulose (any density) or fiberglass (1.8lbs per cubic foot or higher) will probably make a bigger difference.

    Energize CT has various subsidies and financing options for insulating existing single family homes (perhaps your insulation contractor already ran those by you?).

    Air sealing is by far the lowest possible hanging fruit. If you want to more serious air leak chasing on your own, a $200 FLIR attached to your phone and a box fan in a window blowing outward can do a LOT for finding the major entry points. It's possible to air-seal band joists with polyurethane caulk on any wood-to-wood connections, and can-foam on wood-to concrete. Caulk & foam sealed band joists can be insulated with 2-3" cut'n' cobbled reclaimed roofing foam for a lot less than $1500 as a DIY project, but it's time consuming. Cutting the foam 1/2" smaller in width or height than needed allows you to fill in the perimeter with can-foam for a better air seal, and prevents convection from bringing moist air to the now colder band joist.

    Check out Lance Peters' DIY leak-chasing pictures in this thread, using nothing more than a box fan for a "blower door":

    [​IMG]
    [​IMG]
    [​IMG]
     
  17. Dana

    Dana In the trades

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    Just to reiterate a few point:

    A 45,000 BTU/hr load for a 1500' house is about twice what it should be. If the upper floor is actually tight and reasonably insulated, it means there is some truly gross heat leaks elsewhere.

    The uninsulated first floor walls are losing at least twice as much heat as they would be if insulated.

    Depending on how they built-out the attic, there could also be large thermal bypass heat leaks under the floor.

    The basement and rim-joist are clearly part of it, still worth doing, but not the lion's share.

    If insulating the first floor & band joist comes to $6600, and you spent another $1400-1500 on blower door directed air sealing and it brought the heat load down to even 30,000 BTU/hr (it would probably be lower than that), it would be saving 33% of the heating bill even if you kept running it at a ridiculously high 180F. For $50 and some tweaking time you can most likely yield another 7-15% or more in savings, or a 40% reduction in the propane bill. If you've been spending $600/month for the worst 4 months of heating season ($2400) and that gets cut by 40% that's about $1000 in savings just for the winter months, and probably close to $1500 for the year.

    On an $8000 investment even $1000/year would be an internal rate of return (IRR) of over 12%, and if it's saving $1500/year it would be an IRR of about 19%. If you can get subsidized low or no interest financing through Energize CT for those upgrades it's really a no-brainer type investment and would net a positive cash flow. Even without subsidy it's still a good investment even if financed at standard bank rates collateralized by equity in your house. (But don't put it on a credit card, eh?)

    A further point: In the pictures it appears that NONE of the heating system plumbing is insulated. When located in an uninsulated basement the distribution losses of that plumbing are high (quite high, at 180F), and pretty much completely lost. IRC 2015 code minimum for both domestic hot water pipe insulation and heating system plumbing bigger than 3/4" is R3, and at propane prices it's worth insulating ALL the hot water and heating system distribution plumbing that's readily accessible to at least R3.

    [​IMG]
     
  18. Ladiesman217

    Ladiesman217 Member

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    MA


    Maybe you should rent a thermal camera for a ½ or full day. You can check for thermal losses from outside the house. You can check for thermal losses from the rim joists from inside the house. You can look for thermal losses at the ceiling of the top floor.

    You might need your own mini SD memory card to save the images for your records.

    https://www.homedepot.com/tool-truck-rental/Thermal-Camera/FLIR-i7/

    Instruction manual

    http://www.drivecms.com/uploads/sonomacountyenergy.org/Flir_i7_Manual.pdf
     
    Last edited: Mar 21, 2018
  19. Dana

    Dana In the trades

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    At $75/day, $53/half-day by the time you've rented a pistol-grip FLIR three times you may have spent as much as it costs to own the lower res FLIR One, assuming you already have an Android or Apple phone. You'll then have it to check whether the air sealing efforts were successful, and can work different parts of the house on different days weeks or months apart, etc.

    It doesn't even have to be a fully functional current-rev phone to be able to use FLIR One, downloading the images or videos via Wi-Fi. An Android tablet with the micro-USB-C port can use the Android version of the FLIR One which gives you a much bigger display than a phone, if you happen to have one of those.
     
  20. Ladiesman217

    Ladiesman217 Member

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    Perhaps the insulation contractor gave Robenco's house a scan to determine where the house needed insulation.
     
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