House hourly heat loss

[mar13]

In a recent post, @Poindexter mentioned their 1980 Fairbanks AK home loses a degree of heat per hour when it's 0 to negative 20 DF outside. That inspired me to check on my 1983 northwest California house. Using the furnace, it was kept at 66 all day. Turned off the furnace at bedtime and checked 7 hours later. 5 degree loss downstairs with temps averaging near 45 degrees outside during the night - no wind.

Besides local climate, square footage. etc., I think this is a very helpful thing to think about when determining what one's stove needs would be.

 

[EbS-P]

I think it could be a useful metric if you have had consistent temps outside for awhile say a week. We have a basement so I wouldn’t want to do this test until soil temps have bottomed out for the season. Seems like a poor mans manual J calculation. I would want to average several temps across different rooms.

 

[snaple4]

A manual J is a great approach to finding out exactly what rooms loose/gain how much heat. Your method is helpful but there are so many variables you can’t really rely on the findings unless you record everything over a few months time. Call up a few HVAC supply houses for a contractor that does manual j. Some are cheaper. We charge between 250-350 for a simple house.

 

[Poindexter]

My degree loss per hour is not fixed, and is not linear. Haven't googled up to know what J value is.

I lose about one degree per hour in the zero to +20 window.
Around -30 dF I lose about two degrees per hour.

I start losing three degrees per hour around -37dF outdoor ambient and my combined furnace and Blaze King start falling behind when out door ambients reach -50dF.

 

[begreen]

In a recent post, @Poindexter mentioned their 1980 Fairbanks AK home loses a degree of heat per hour when it's 0 to negative 20 DF outside. That inspired me to check on my 1983 northwest California house. Using the furnace, it was kept at 66 all day. Turned off the furnace at bedtime and checked 7 hours later. 5 degree loss downstairs with temps averaging near 45 degrees outside during the night - no wind.

Besides local climate, square footage. etc., I think this is a very helpful thing to think about when determining what one's stove needs would be.

Wind is another major factor. It would be interesting to this test again with the storm that is hitting and compare. Stay safe out there. Looks like the upper CA coast is due for a doozy of storm. I just passed through the Siskiyous on Sunday. They are supposed to get a couple feet of snow with this storm.

 

[mar13]

I just googled J manual last night and will read more about it later. Probably deeper than I intend to go until I do an addition.

We were without power for a few hours so used the stove to heat up some dinner. The roads are a mess with branches and did see one small eucalyptus blocking an off ramp. (I did wonder who was getting that wood.) Power lines down around town, with the wildest to hit later tonight. Sticking close to home. After the storm, we'll experience some sub32 temps, which is unusual for us. Cliff Mass' weather blogspot had a good write up of the storm. (Meteorological bomb!)

 

[Mech e]

Heat loss rate is nonlinear in the OPs example assuming the outside air temperature remains constant. As the temperature in the house drops, so will the rate of heat loss.

 

[peakbagger]

The flaw in the concept is thermal mass. If a house has a lot of thermal mass, the mass is going to give off stored heat for a long time keeping the house warm. That is the concept used in a lot of low/no energy homes. Sun heat up the mass during the day and the building coasts overnigth (or actually for a couple of days). Manual J looks strictly at active heat loss. The trade off for thermal mass is it takes a long time to heat the place back up. Folks with radiant slabs know this and they rarely use setback thermostats as it takesa long time to get back to room temp.

 

[thunderhead]

In addition to insulation wind and temp, You have to figure cloud coverage too, and whether the sun is up or not on the radiation side, both incoming and outgoing. These are partly accounted for by air temperature, but not entirely. Total energy budget can get complex.

 

[Poindexter]

If you are losing extra heat in wind that is a good time to get some blue chalk and go looking for air leaks. Around windows especially, also jiffy boxes like light switches and receptacles on exterior walls.

When I started out fixing up the current house I would just mark them with blue chalk in winter and then fix them in the summer. Pencil works OK, another option would be "summer chore" folder in the gallery on your smartphone.

Also be highly suspicious of floor joists. If the exterior wall of a downstairs room feels cold near the ceiling, and the floor of the room over head also feels cold you might have a gap in your insulation where the floor joists are resting on the header of the lower floor. Don't ask how I figured that one out.

When I finally figured out how to get window trim off without wrecking it the wife wanted new trim to anyway, to match the new trim on the windows where I had already wrecked the old trim while fixing air leaks.

At the end of the day the guy who built your house does not care about your energy bills as much as you do.

 

[Poindexter]

I thought of a couple other things about air leaks around windows.

If you are pulling the trim to fix an air leak, pay the extra two dollars for spray foam insulation that says "doors and windows" on the package. The cheaper stuff is cheaper insulation today, but replacing cracked glass later is expensive.

For trim, you pay your money you take your chances.

If you insist on using the really cheap pre-finished stuff from the home store pick through the stacks carefully. If you can see the center of the tree in the finished trim it will crack and split, it is a when not if question.

Also, it doesn't matter how square your saw is at zero. Before you cut the good stuff run a scrap 2x4 through there making four pieces with a 45 degree miter at both ends - and flip the 2x4 180 degrees for every cut. Try fitting those 2x4 scraps together before you start hacking up trim. Adjust. Try again. Then run it again on another scrap without flipping the 2x4 scrap for every cut. Adjust. Do check your blade for flatness before you toss a mitered scrap of 2x4 through the drywall in the garage.

If you spend four hours setting up your saw and 8 minutes cutting your trim it is time well spent.

For bedrooms I am still using Hemlock moulding for my interior trim less the sill. I use poplar for the sills. Poplar is relatively cheap for the three advantages it brings to window sills. Poplar machines easily, takes paint well and is mold resistant. Hemlock is stringy and hard to trim the miters on, but it is very cheap already milled and I finish the iron in my block plane on a leather strop after honing to 4000 grit.

If you can't finish a plane iron on a leather strop you might could trim miters on hemlock with a fresh blade in a drywall knife, but take your time, work from the back and remember Hemlock is stringy. A more expensive alternative would be to get poplar mouldling from a local to you custom millwork shop. Poplar face and edge grain comes out pretty nice at 600 grit, for end grain you can get away with going to 1000 grit, most of the time on your irons, and then sand the wood easily and quickly, ready to paint.

Also, for your first window get the sill in. Then make and tack into place (without driving the nails home) your two interior verticals. Once those are tacked in make you top horizontal about half inch too long and test fit it. No wall I ever put window trim on was acutally flat. Test fit it both flat to the wall, and with the bottom edge tipped away from the wall to check the length of your top piece on the outer length dimension.