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Community and Q&A

Airtight and ultra-insulated home feels cold all the time

Zuhl | Posted in General Questions on

My wife and I just built a 1.5-story home that is 2700 square feet down 800 up. The downstairs has a 4 ton Trane XR15 air conditioner and the upstairs has a 2 Ton XR15 air conditioner. Heat is run on propane since we don’t have natural gas in our area.

Our walls are 6″ thick and filled with cellulose. Before insulation was applied I sealed EVERY seam, crack, nook, or cranny with spray foam or caulk. I did not bother with the expense of a blower test, but it should be very tight. The attic is vented and the ceiling has about 21″ of Insulation on it. Way more than is ever used in Houston, Texas. Low-E SC windows throughout.

Anyway, for all this, it always feels freezing cold to us. At 70 degrees in the winter we have to wear a coat. We are not really comfortable until we hit about 72-73 degrees, which seems pretty high to me. In our old house, we use to keep it at 70. The odd thing is that in summer we have too cool it colder as well to be comfortable. About 75 degrees, whereas our old house we kept at 78. Of course it ran non-stop to get down to 78.

Could this very small disparity in our perceived comfortable temperature be do somehow to the tightness of the home? Convection from outside sources are all but negated. Radiation through the windows should be minimized. The only effects we should be getting is radiative heat to the walls. I measured them to be about 67 degrees when it was 30 degrees outside.

Part of me wonders if it is because the heater/AC runs so much less and therefore the air does not feel as comfortable. I knew a two stage unit would have been better, but we had to cut corners somewhere to afford this thing.

Another thing to note is that the upstairs feels warmer even at a lower temperature. We can be up there at 69-70 degrees with no problem at all in the winter. We almost NEVER run that unit since the heat from downstairs rises up there.

any thoughts are appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Different people require different indoor temperatures to feel comfortable. There is no "right" indoor temperature. If you feel comfortable, then the temperature is correct.

    As we get older, we generally prefer warmer indoor temperatures than when we were younger. One thing is certain: you and your wife are both two years older than you were two years ago.

    That said, you may want to check a few things:

    Buy 6 or 7 thermometers and put therm in various places around your house. Put some of them about 12 inches above the floor, and others 5 feet above the floor. Put some of them upstairs, and some of them downstairs.

    Maybe your indoor air temperatures are exactly the same as your thermostat settings, but maybe they are different.

  2. dickrussell | | #2

    The first thing that came to mind here is that maybe the interior is humid from lack of ventilation. Presumably the house indeed is tight from all that air sealing, and the moisture produced by human occupancy builds up. Perhaps the owners feel chilled if the air at 70 is more humid than in their old house at the same 70. In summer, that six tons of AC probably is too much, and the units don't run long enough to dehumidify, forcing a lower setpoint to get the moisture out.

  3. wjrobinson | | #3

    3500sqft home with no room in the budget for a blower door test, interesting. You are trying to figure this all out yourself and you are there. We all are not. There is so much to read at this site for free. You could even join and have access to even more. Maybe you can then figure this all out.

    You didn't post as to any continuous insulation, or spray foams or where your ducts are, or if you used R 5 triple pane windows or if you are running any vent systems, or if your floor coverings are different from your previous home.

    If your home is functioning properly I would just set the temperature where you want it.

    I doubt anyone on the internet can do as much as someone visiting your home. What do your trades people that installed your HVAC and insulation have to say... ?

    IMO... if your last home was way less efficient then the nice hot heat from the registers felt nicer than a modern 96% system will and same for AC... your AC past may have been on much more blowing more cold air and moving the air around you more.... This is my bet...

  4. Zuhl | | #4

    We did not do every possible thing to make the green gods happy. Electricity is just too cheap in Texas to ever see a return on that investment. We have a vented attic. Boo. We have exposed ducts with only R8 insulation on them. Boo. But in the summer we were consuming only an average of 50kw/H per day. We have 100 degree summers and this is a 3500 sq ft home. Our old 1600 sq. ft home consumed 47 kWh per day ($160 month). So I think we did alright on cooling. My concern however is the amount of propane we consume. It is considerably more expensive and is way more costly than our old natural gas furnace. And feeling colder means we run the furnace more than I would like.

    Our house is primarily conditioned by the 4 ton on the 2700 ft downstairs. the 2 ton up almost is never used. Average summer RH is around 65, winter is around 35-40. In Houston we are above 90% RH almost all the time unless a cold front comes through. Maybe a dual stage would have been better but again, finances and ROI dictated build because we would never recoup the investment otherwise.

    The point of this question was not wild speculation over a million variables or to incite criticism of what we did or did not do. I am satisfied that we did it pretty good for a $250K budget on the build. My question was to wonder whether folks see different trends in heating and cooling in tight and efficient homes than in lesser built ones.

  5. GBA Editor
    Martin Holladay | | #5

    There is no reason to believe that a tight, well insulated home:

    (a) will feel less comfortable at the same indoor temperature than a poorly insulated home, or

    (b) will require higher thermostat settings in winter or lower thermostat settings in summer for occupant comfort than a poorly insulated home, or

    (c) will have higher energy bills than a poorly insulated home.

    Once again, I urge you to verify with thermometers and one or two hygrometers that your indoor conditions are at the setpoints where you assume they are. In general, I would agree with AJ's advice: just set your thermostat to whatever setting makes you feel comfortable, and don't worry about it.

    Some homes in your climate need supplemental dehumidification during the summer. The easiest way to do that is to install a $250 stand-alone dehumidifier.

    Finally, you are correct that propane is an expensive fuel (especially compared to natural gas). One way to lower your heating bills is to begin installing a few ductless miniplit units, and using them for heating during the winter. They will cost less to operate than your propane furnace.

    Come to think of it, this solution would make your air conditioner unnecessary, if you installed enough of the minisplit units. It's a little late for that, probably, at your house, but the suggestion is worth considering for any GBA readers who are considering the use of a propane furnace.

  6. davidmeiland | | #6

    Why not simply swap out the A/C condensers for heat pumps and stop using propane?

  7. Zuhl | | #7

    I may ultimately swap away from the propane. I need to look into what it would cost to run a heat pump instead of my gas furnace. There is a small change we may be getting NG in our area soon. That would be perfect if that happened.

    What I don't get about propane is that it is has more energy in it than NG, but appliances never produce as much heat on it. Save more my stove. It is a Dacor designed specifically for LPG. That thing gets HOT!

  8. GBA Editor
    Martin Holladay | | #8

    The heat output of a furnace or a water heater has nothing to do with the fuel; it only has to do with the appliance's rated output. You can get a propane furnace rated at 80,000 Btuh if you want -- and it will produce exactly as much heat as a natural-gas furnace rated at 80,000 Btuh.

    A propane furnace rated at 80,000 Btuh will produce twice as much heat per hour as a natural-gas furnace rated at 40,000 Btuh. So if you have an appliance that is disappointing you because of its feeble heat output, perhaps you chose one with the wrong specs.

  9. user-1072251 | | #9

    three items from your posts:
    "we did not bother with the expense of a blower test"
    this is not really a "bother", but a necessary tool, the same way a screwdriver is necessary for installing a screw. Pretty hard to install a screw without the driver; same goes for a blower door test - hard to determine if there is a problem without the tool to check.

    We did not do every possible thing to make the green gods happy
    Building a good house is about long term comfort, sustainability and keeping expenses down, not about vauge religious type ideals (although this does enter the picture occasionally). Sounds like there is something wrong with your house. Hire an energy auditor to find it.

    lastly: "wonder whether folks see different trends in heating and cooling in tight and efficient homes than in lesser built ones." Absolutely! The houses I'm building today are a world apart from the code houses I built 15 years ago. Comfort level is higher, cost to heat is far lower; temperatures are consistent throughout the home, humidity levels far more comfortable, interior temperatures are buffered by the insulation levels and air tightness. And we're now using air source heat pumps which are much less expensive to buy and install, and far cheaper to run. My one complaint is that these houses "live" so differently that people really can't comprehend until they move in.

    If your house is well insulated for your climate, airtight, and has the proper ventilation systems, I would not expect any of the problems you are describing to be happening. Hope you can get this figured out so you can enjoy the house.

  10. KeithH | | #10

    Just a DIYer here. I lived in Houston for several years and think that the experts above who mentioned humidity are on the right track. High indoor humidity will make temperatures that you would otherwise be comfortable at very uncomfortable. As you likely know, 40 F in Houston can feel much colder than 25 F in Denver. Perhaps your HVAC equipment doesn't reduce the indoor humidity unless it has the longer run times that your 72 F thermostat generates. You could probably do some experiments with those temperature and humidity monitors that Martin suggested buying. See if your humidity rises at lower or higher temperatures. Since the humidity available in Houston is large, you could try 65 and 75 F as well.

    Along the same thought: is there any chance that you have a source of humidity in your new house that wasn't in your old one? No bathroom exhaust fan? Dirt crawl space floor? No vapor barrier under the concrete slab? etc.

    I think the advice to get an energy audit is sound. Here in the greater Denver area, we were able to get an energy audit with a blower door test for $150. Since that is about 1.5 hrs of HVAC service labor, it might pay off. Of course, the auditor probably won't be able to help you with the humidity question ...

  11. LucyF | | #11


    I'm in the South as well - South Carolina. One factor may be that this is a MUCH colder winter than we have had in years. Last year we had a few cold spells with frost, but mostly it was not cold. This year, I've got a shady patch of lawn in which the ground was frozen for days. That may one reason you feel colder and less comfortable this winter.

  12. Expert Member
    Dana Dorsett | | #12

    I can't get past the idea that 50kwh/day is being talked up as LOW power use for a 3500' house, even at 100F outdoor temps plus the high latent loads of Houston! (There must be a lot of west-facing glass or something?)

    Moving the ducts & air handler inside the thermal & pressure boundary of the house would peel something on the order of 10kwh/day off that cooling season average, and seriously air sealing the house would deliver another 5-10kwh/day in savings. Bringing it under 30kwh/day during 100F weather would be impressive as a retrofit, but not that difficult during the design & site considerations phase (unless you have a penchant for brightly lit ceilings full of 75watt R40s or something.)

    Average residential retail power rates in TX are about 9 cents/kwh, but at the continued fall in installed cost of grid tied photovoltaics it's likely that the lifecycle cost of rooftop PV is now lower than that 9 cents after applying ANY subsidy, and will be downright cheap in areas where the PV market is competitive. (I've read discussions that some locations in TX will be hitting the $1.50/watt all-in installed cost BEFORE subsidy in 2014. Five years ago that wouldn't even buy you the panels!)

    An average heating season coefficient of performance (COP) of 2.5 (you'd do a COP of about 4 with mini-splits), your heat pump would deliver about (2.5 x 3412 BTU/kwh = ) 8500 BTU per kwh. At 9 cents/kwh that's ~95,000 BTU/$.

    That's the same as buck-a-therm natural gas burned in a 95% efficiency gas burner.

    A condensing propane furnace with a 95% AFUE delivers about (0.95 x 92,000=) 87,400BTU / gallon, so heating with the heat pump will be the same as heating with (87,400 / 95,000 = ) $0.92 /gallon propane. (I'd be surprised if home-delivered retail propane has been that cheap in TX for at least a decade.)

    A mini-split would be substantially cheaper to heat with than any single-speed ducted heat pump- comparable to 55-60 cent propane.

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