How much heat does your house lose?

[raygard]

I have noticed that I loose 1° per hour. I have a 1978 2 storey house with a brick front and siding for the other sides and an asphalt shingle roof. There's plenty of insulation, or so I thought, in the "attic" space. I think I am losing the majority of my heat through the walls (there is only some pithy blue board insulation in the walls). Does anyone else know how much heat they loose from their house by way of degrees per hour?

Ray

 

[woodgeek]

I think most conventional houses are going to be in the 1-2°F/hr range when it is freezing out. If you don't mind shutting off your heat for a few hours, it is one way to get a benchmark. There are two rubs....one is that some rooms might cool off faster than others...how do you decide what temp to use and the other is that your housemates might not like being cold for several hours to get a data point.

Personally, I always found it easier to time the cycling of my central heater, and multiply by its nominal output, to get my demand at a given temp. I started out doing this with a stopwatch while I was watching the TV (and could hear the boiler kick on and off). The advantage is that you can get more data points that are quite accurate....you can see the effects of high winds, modest insulation upgrades, etc.

A 'fun' thing is to combine both of our data....if I know my house needs 20kBTU/h at some temp, and it drops 1°/h, e.g. during a blackout, I know that my house has a built in thermal storage capacity of 20 kBTU/degF.

On a related note, in very efficient houses with very low cooling rates, e.g. passiv houses, the heating systems are rather small and used infrequently....making it hard to use my timing method. I recently went to a presentation by a speaker from the French DOE that had validated your approach (over a rather long timeline) as a method for certifying energy efficiency in new construction.

 

[lukem]

I posted a similar thread a while back:

https://www.hearth.com/econtent/index.php/forums/viewthread/78962/

I haven't updated since it got colder, but I leat the stove go out a couple nights recently and the low outside temp was low 30's and I lost 6 degree in 10 hours. My house depends a lot on the weather the day before. If it is sunny the brick veneer soaks up a lot of heat and I don't loose much. Good thing I have 24" overhangs or the summer would be brutal.

 

[Dakotas Dad]

At night, calm, above freezing we will lose about .3F an hour. below freezing, with a wind, it can get as bad as 1.2F or so an hour. We have a fair amount of glass to bring in some solar heating during the day, and in fact above 45F or so and calm, the sun will raise the temps about the same as the night loss rate.

 

[maverick06]

75-85 MBTU / winter

All over the place per hour depending on so many things (mainly temperature differential, wind, rain, snow, sun, and how long the house was at that temperature, did it soak it into everything). Honestly cant guess

 

[woodgeek]

Mine is ~0.6°F/hr, at 32°F, calm outside. Used to be twice that before airsealing.

 

[TradEddie]

One "official" way to benchmark something like this is to calculate your BTU/HDD/SQFT.
For oil or gas heat, you take your season heating bill and calculate the BTUs used (see online for conversion), divide this by the heating degree days for your area then divide by the square footage of your home. The EPA did a survey to determine the typical range of homes. Mine came out to a little over 4 BTU/HDD/SQFT, which is better than average but excludes the wood I burn each year. This number represents the efficiency of you heating appliances and your insulation, but obviously it can be significantly affected by how much you heat your house, and how many days you are at home.

To your original question, my house loses about 1F/hr when its about freezing outside.

TE

 

[raygard]

I am pleased to see that as leaky as my house is, that loosing the 1°/hr seems not unheard of. I am going to go to proverbial "town" though and airseal everything I can in trying to lower that heat loss as Woodgeek said. And will remain in awe of the 0.3°/hour loss at freezing as Dakota states.

I have a lot to learn.

Thanks for the input. I don't feel like such a chump now.

Ray

 

[thinkxingu]

Last night it was 12* and our house, with no heat on, went from 74 to 65 in 8.5 hours (9:30-6), or just over 1*/hr. We've noticed the temp. drop is exponential with wind and temp. For example, at triple the temp (32*), we lose about .5*/hr.

S

 

[jharkin]

One "official" way to benchmark something like this is to calculate your BTU/HDD/SQFT.
For oil or gas heat, you take your season heating bill and calculate the BTUs used (see online for conversion), divide this by the heating degree days for your area then divide by the square footage of your home. The EPA did a survey to determine the typical range of homes. Mine came out to a little over 4 BTU/HDD/SQFT, which is better than average but excludes the wood I burn each year. This number represents the efficiency of you heating appliances and your insulation, but obviously it can be significantly affected by how much you heat your house, and how many days you are at home.

To your original question, my house loses about 1F/hr when its about freezing outside.

TE

+1

I did the math this way for the last two winters to generate a baseline for judging the improvements when we did insulation work. Figures were around 12 the last two winters - based on NG & wood burned x relative efficiency. This year after all the improvements its working out to roughly 9. From what I've read, as high as 25+ is possible for a completely uninsulated old house, typical new construction is 5-7, a super tight house is under 5, and a passive house is something like 1.

Based on that I'm quite impressed I could hit 9 with retrofit insulation.

In terms of degrees per hour I couldn't tell you, as we never leave the heat off long enough to figure that out Any figures will be hard to compare as there are so many variables - inside temp, outside temp, insulation, ratio of wall/roof area to sq footage, # windows, solar gain, and on and on and on.

 

[Pallet Pete]

Well Ray we loose so much so fast that if we get to 65 with the furnace not the stove it goes down to 55 within a half hour. ( no joke ) We are getting insulation this week

Pete

 

[eclecticcottage]

I was just saying we should have one of those whole house energy evaluations done. It would be fun to have them out, without a furnace for them to test!

Lesse...I think 1 degree an hour seems right for us too.

 

[jebatty]

One “official†way to benchmark something like this is to calculate your BTU/HDD/SQFT.

Applied this to our house, built in 1956 but substantially rebuilt and insulated since, new windows, etc. 1500 sq ft main level, 1500 sq feet below grade basement. House is heated with a wood stove main level, electric to keep basement at 45-50F, and electric for whole house if we take off for more than a day during the heating season when there is a danger of freezing. Wood used per year is 4-5 cords of aspen (or 4.5 cords for the computation), electric heat on a separate meter and that totals 1890 kwh/yr. Heating degree days reported by weather station 12 miles away for Feb 2011 - Jan 2012 was 10,400.

Total heating btu = (13.2 million/aspen cord of wood x 4.5) + (1890 x 3400/kwh for electric) = 65,826,000 btu/yr / 10400 HDD / 3000 = 2.1 btu/sq ft for total living space or 4.2 btu/sq ft for building footprint.

If I use total electric (DHW, lights, computer, TV, electric stove/oven, etc.), our only other energy source, that was 11959 kwh including heating for the same period. New computation is 3.2 btu/sq ft for total living space or 6.4 btu/sq ft for building footprint.

 

[jharkin]

hmmm if we are counting unfinished basement in the math my figures drop from 12 and 9. Down to 9 and 6.......

 

[woodgeek]

I am also a fan of the Home Heating Index (HHI) as a benchmark.....its easy to compute and its data, unlike the LEED cert, HERS score, Energy Star cert, etc. that require a professional to evaluate and whose details and definitions are always changing.

If I compute the number of BTUs I make and deliver for space heating, divided by HDD*sqft, the number I got for my 1960 split level was 10-11 when I moved in in 2005. After tweaking the weather stripping on the original windows, airsealing the attic floor and strategic insulation upgrades, I am now at ~5. If I include additional BTUs I get from appliances and solar gain, my scores would be 12 originally and 6 now.

jebatty--your numbers are great....do you run the upstairs at a temp corresponding to the 'base' of the HDD, or do you run it cooler? The cooler basement is improving your score relative to heating all the sqft to 65°F. But, of course, it does reflect conservation.

 

[jebatty]

do you run the upstairs at a temp corresponding to the ‘base’ of the HDD, or do you run it cooler? The cooler basement is improving your score relative to heating all the sqft to 65°F.

Upstairs temp was calculated based on 70F for the HDD. Right, did not compensate for the colder basement.

 

[TradEddie]

Since moving into our house 8 years ago,I've replaced most of the 30+ year old windows, improved insulation behind knee walls, air sealed vast areas of the basement, and just about every other thing I can think of that doesn't require ripping out walls to re-insulate. Unfortunately, none of this has had any noticeable effect. I hope that's because there are too many other variables affecting how much heat we use but also, it's a case of diminishing returns as you get to the lower numbers.

TE

 

[Weird tolkienish figure]

I have noticed that I loose 1° per hour. I have a 1978 2 storey house with a brick front and siding for the other sides and an asphalt shingle roof. There's plenty of insulation, or so I thought, in the "attic" space. I think I am losing the majority of my heat through the walls (there is only some pithy blue board insulation in the walls). Does anyone else know how much heat they loose from their house by way of degrees per hour?

Ray

I'm probably on the upper end of heat loss. As a plus, I get a lot of solar gain, I have huge 1960's modernist windows in front of the house, the solar gain is very noticeable. I turn the heat off all the time, but it stays at 45, it's the lowest the thermostat will go, and I'd never want it to get below that and suffer frozen pipes, etc. But every day when I get home from work the temperature of the house is in the lower-mid 50's, with no heat on. On the coldest day this year it was actually at 46 or so... and we had no sun on that day too.

But yeah, I'll probably need the cotton candy blown in at some point. I just bought the house and didn't want to deal with it this year.

 

[TradEddie]

You really should not change the base temperature for HDD from 65F (assuming you're in the US) even if you have your thermostat at 70F. HDD is a measure of the local climate, not your conservation efforts (or lack of). If everyone uses different bases, it would be even more meaningless to compare numbers. In practice, if 70F is your comfort level, you probably don't use heat unless outside temps fall below 65F, this is why 65F is the common base temperature in the US.

There are so many problems with this index, that it probably doesn't matter anyway. Use it to get a ballpark estimate, don't read too much into it. Everyone's heating demand is different, my own changes dramatically from year to year depending on employment, visitors, sick days, snow days, etc., I can't compare my own historical numbers, never mind compare with anyone else.

TE

 

[Weird tolkienish figure]

You really should not change the base temperature for HDD from 65F (assuming you're in the US) even if you have your thermostat at 70F. HDD is a measure of the local climate, not your conservation efforts (or lack of). If everyone uses different bases, it would be even more meaningless to compare numbers. In practice, if 70F is your comfort level, you probably don't use heat unless outside temps fall below 65F, this is why 65F is the common base temperature in the US.

There are so many problems with this index, that it probably doesn't matter anyway. Use it to get a ballpark estimate, don't read too much into it. Everyone's heating demand is different, my own changes dramatically from year to year depending on employment, visitors, sick days, snow days, etc., I can't compare my own historical numbers, never mind compare with anyone else.

TE

I've googled it and it seems as if you're right. I'm still trying to figure out this basement problem. I guess it's possible I also have a broken thermostat.

What they need to do is invent a "thermostat" with the added function of being able to set you home at the desired humidity too...

 

[raygard]

Well Ray we loose so much so fast that if we get to 65 with the furnace not the stove it goes down to 55 within a half hour. ( no joke ) We are getting insulation this week
Pete

How interesting Pete. I'm not as fast in the drop from 65° to 55°, ours is about 2.5 to 3 hours. There must be some critical factor that when the house temp drops below a certian point then, unless you put energy into maintain, it will start to drop to match that of the outside. We can though, hold at 55° for quite a while before it plumets again.

Ray

 

[SmokeyTheBear]

Heat loss is proportional to the difference in temperature considering conduction effects only. As inside temperature approaches that of outdoors the rate of loss will slow down and eventually reach 0 loss.

 

[TradEddie]

I just found this interesting report from Canada yesterday:

https://www03.cmhc-schl.gc.ca/catalog/productDetail.cfm?cat=45&itm=9&lang=en&fr=1330103567937

They did a really extensive study on efficiency of thermostat setback, but this report only gives a brief summary, pity more of the information isn't included. This was for a well insulated modern home and with an overnight temperature of 17F, this house still lost about 1F/hr. When temperatures were above freezing, they said heat loss was so low that no energy savings were achieved by thermostat setback, but unfortunately they don't give the heat loss rate at any higher outside temperatures.

I've been watching mine for a few days now, and I'm losing 6-7F in 7 hours every night, even though outside temperatures have been anywhere from 30F to 47F.

TE

 

[raygard]

I experience though TE that same 6-7F in 7 hour loss per night. I have notice though. That if I run the stove for several days and the whole house is warm and so are the materials and not just the air then I'll lose only 3 or 4F overnight.

The loss is really quite depressing. If I ever met the builder of this house I would really give him a "what for". The next house I buy, I swear, is going to be in the middle of Death Valley. That should eliminate some of the cold problems.

Ray

 

[Hass]

It depends a lot on how warm your house is too!

If you keep your house at 90 degrees, it will fall much faster than someone who keeps their house at 65.