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Old 12-24-2010, 06:17 PM   #1
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House Heat Loss

Hi All,

This my first post on this forum, but I have read hundreds of topics and I'd like to thank everyone for great posts, answers and suggestions.

I have a question regarding house heat loss in winter. I am trying to find formula to see how my house ready for the winter.

I have measured that when outside the house is 32F and inside is 68F and I turn off my furnace my house loses 5F in about 6 hours. My thermostat is set to turn off at midnight at 68F and starts only when temperature reaches 63F, so it takes about 6 hours to my house to cool down to 63F.

I've spoke with folks at work and they said it is very good numbers and my house has good insulation.

Just wanted to see if someone knows what good numbers for good insulated house are.

Best Regards,


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Old 12-24-2010, 07:01 PM   #2
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i have never measured # like this before but what i would do is look at your heating bill and if you are ok paying that then your # are probably good lol!!


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Old 12-25-2010, 06:14 PM   #3
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If you want an accurate idea how energy efficient the house is you can do thermal scans that show cold spots or do a house tightness test with a blower door. Both are not DIY, but you will see where the issues are and you can take care of the remedies.
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Old 12-25-2010, 08:57 PM   #4
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Old 12-26-2010, 11:14 AM   #5
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I had a brick built house with open gas fires that were on 24/7.
When I had to turn the gas off to connect our newly installed boiler and baseboard heating the place kept warm for three days.

The secret with heating like that is mass, with good insulation, the bricks held a great deal of heat that was gradually released.
The baseboard heating worked exactly the same, once fitted it was on 24/7 for twenty eight years, summer and winter until I sold the place.

The trouble with mass is it slow to heat up, but once warm keeps the place at a steady temperature.

These days the move is towards under floor heating, with large concrete slabs to collect the heat and with large East, South and West facing windows, the floors collect the heat from the sun during the day and have a slow heat release over night.
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Old 12-26-2010, 12:06 PM   #6
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Kirsch -

There are a number of holes in your approach:

1. You are comparing to others to look at adequacy and not what is right. They could easily have the same problems as you.

2. You were only looking at a very short period when it was convenient to shut of the heat when it was not really cold. That is not an excuse to not look at really accurately determining where some short term problems are. These were illustrated by heat loss from air infiltration and radient heat loss that varies during the day and needs professional interpretation since some may just be short term surface radiation from veneers that are just shedding excess surface heat absorbed by the sun.

3. Windows and orientation can have an effect, even if they are always a "hole in the wall" with some supper gas and separation, the "R-values" never appraoch a wall, even if it is insulated with fiberglass and installed properly, which is rare. The biggest problem is radient heat loss that is never talked about and increases dramatically as temperatures go down. An uncovered window will drain energy from a house.

4. the big problem is that you have a lightweight structure using lab results for insulation materials over a short period test. An R-19 can actually provide a real wall insulation values (still short term - hours) of between a R-11 and R-17 depending on the stud materials and spacing. - This is you are a fan of the lab "R-value" nymbers that can be made to sell well.

5. Perry525 hit on a big point in mentioning heat storage and being huge, over-riding benefit. The U.S. and Canada are probably small portion of the housing in the world that is lightweight, temporary materials. This is pointed out by the lack of need of energy to survive and is related to low cost construction, temporary housing locations and advertising concepts.

I built and all masonry lake home (1850 sf, block walls, 2" XPS and brick exterior. It had 4 -6' sliding doors and 3 other windows facing south. In late Sept, early Oct, I did some electrical work and shut off the furnace circuits. The thermostat was set at 63F. I returned on December 15 after several day stretches of -10F. When I got there in the morning, the temperature was still 65F, so apparently the furnace had not run and was verified by the gas company that called me because they could not add to the LP tank for scheduled top-off. All I did was pull the blinds on the windows and left the sliding doors uncovered, so they could allow the southern sun in (low angle, but clear) heat the concrete floor inside. This heat reservoir kept everything warm. I should have had a clue when during a previous year my settings with a set-back to 40F for evenings and 65F for days was only $30 cheaper for an entire year and was as warm and cozy as when I came for my long winter week-ends.

You have the kind of structure yoiu have, so just gets some tests to find when you are losing energy. The air flow/infiltration is fist because closing air gaps is the easiest and cheaper.

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Old 12-26-2010, 10:58 PM   #7
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You can ball park your heat loss, too. Look at your annual heating btu's and divide that by the square footage of the house. If you are losing in the neighborhood of 10 btu/hr/sq ft you are doing OK. Somewhere around 5 is very good, and PassivHaus standards, which are off the charts, are into the fractions (below 1, if I recall). You can tweak that a tad by using about 90-80% of the fuel usage for heating if you also heat domestic water w/ that same appliance. Etc. But, that'll tell you reasonably well how she sits.


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