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Home heat loss calculation

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Posted by Curbie on December 1, 2010, 10:59 pm
I was wondering if anyone has problems with this ways of calculation
house-hold heat loss?



Posted by Ecnerwal on December 2, 2010, 1:46 am

Well, since you failed to specify a way, I have no problem with it.

It is engineering. It's not rocket science. If you can run a
spreadsheet, you can calculate it as finely as you care to account for
all the parts of your house. If not, you can't. If you assume your house
is built better than it is actually built, it will not give an accurate
indication of actual energy use, but that's a matter of the accuracy of
your model, not the standard equations of heat flow.

Useful approximations - 13.9 cubic feet per pound of air, specific heat
of air 0.24, 3413 btu/KWh, 91,500 btu/gallon propane, 138,000 btu/gallon
fuel oil. U-value = 1/R-value. Area (square feet) times u-value = heat
flow per degree F differential. Grab some climactic data and you can
compute yearly use at least two different ways (by degree-days and by
average temperatures) as well as size your heating appliances for
worst-case low temperatures and desired indoor temperature. Compare that
to what you actually use for a year and you can figure out if your model
is accurate.

Or, if you are not all that detail oriented, you can go to someplace
and get a general idea based on reality-based assumptions.

With any method, garbage in == garbage out applies.

Cats, coffee, chocolate...vices to live by

Posted by Jim Wilkins on December 2, 2010, 1:36 pm
 On Dec 1, 8:46pm, Ecnerwal

That's the core of the problem, good measurements. You can find heat
leaks with a thermal imager, an IR thermometer, or by photographing
the snow melt pattern on your roof. All a model can tell you is to
keep looking. I used indoor humidity to decide when the house was
tight enough.

Radio Shack remote thermometers are helpful. I'm still looking for a
cheap second-hand multichannel temperature logger. The ones I've used
cost more than I could ever save:


Posted by Curbie on December 2, 2010, 4:04 pm
 On Thu, 2 Dec 2010 05:36:02 -0800 (PST), Jim Wilkins

Could you explain this a little more, it would seem that more humidity
= tighter, but tight is too tight?


Posted by Jim Wilkins on December 2, 2010, 5:55 pm
When the midwinter humidity rose to ~50% I stopped tightening the
doors and windows. I had started at the top and worked downwards,
leaving known leaks in the basement to let in combustion air.

Another measure is the time for cooking smells to dissipate, about 3
hours for frying onions.


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