Can this Btu/hr loss be correct???

[Thom Griffin]

I just did the Slant/Fin heat loss for my home: 1770 sq ft bottom floor, old 1830's house; unheated upstairs, roughly 3 1/2" insulation in walls, uninsulated floor, and 6" of insulation above unheated 2nd floor; lots of windows; all of them low-E double pane, however, field stone foundation, so lots of air infiltration.

After entering all the data, the software says the heat loss is 83,451 Btu/hr figured at 0 F outdoor temp and 70 indoors.

Does this seem at all correct? I'm mostly doing this to change a few radiators and balance the heat a bit better. I'm just curious, as the loss seems rather low to me.

 

[Frozen Canuck]

I'm just curious, as the loss seems rather low to me.

Omg…..thats more than double my loss at design temp of -40. Draft sealing & insulation will save you a ton. Really those who own/service 1830's housing maybe your best resource on the accuracy of those numbers. I just can't imagine creating/buying those btu's/sqft/hr in my area.

 

[Thom Griffin]

Well...of course draft sealing would be a great idea. Considering that the house is wrapped in Tyvek, then plank sheathing, granted has only 3 1/2 " of insulation (my wife wanted to be able to see the posts and beams...), and then a plastic vapor wrap and wallboard with a skim coat of real plaster. It's surprising to me just how much air infiltration there is. As I said in my original post, the house has a field stone foundation, so the house "moves" a bit, hence the leakage around the fancy windows. Last year I put up good old triple track aluminum storms and they helped a lot. I just need to do the other half of the house.

There's not much room for any more insulation. As long as it's not windy my Tarm stays ahead of it quite nicely. I just wanted to balance the heat a bit better, and was curious as to my Btu/hr totals.

 

[Frozen Canuck]

What some have done here with the old field stone foundations is inject high density foam between any 2 stones that will take it. Great draft seal & insulator. Possible downside is the bugs like it too. So one has to prevent insect entry & that could be tough in an 1800's home.

 

[Thom Griffin]

The storm windows really cut down on the "wind" inside. If I can afford it, I'll do the other half this coming year. As for the basement, I was thinking of reflectix in between all of the timber joists. I know the preferred method would be to run along the bottom of the joists to make a plenum, but that would just make a huge mouse nest in an old house.

I must say, I was not aware that insects would eat the foam insulation. What about rigid foam? I've considered taking off the siding and sheathing,(replacing the sheathing) putting up rigid foam in between whatever studs there are, and sealing it in with spray foam; but if the insects are going to eat the sprayed stuff, what's the point? Plus, I'm pretty certain that taking off the siding, would be a real pain, resulting in many cracked pieces. I do wish I had replaced the sheathing when I renovated in the early 90's.

 

[laynes69]

That's quite a bit of heat loss. Have you had a blower door test done to verify heat exchanges per hour? We have a mid 19th century Victorian that's 2500 sqft and our heat loss after having a blower door test came out at around 75,000 btu an hour at 0 degrees with 70* inside.

We have 6" walls that are insulated and that helps, but of course our basement is a huge culprit. Half the foundation is block, the other half is field stone. During the blower door test, I was suprised on the amount of air that entered the stone walls. We have 42 windows and they are newer vinyl windows and still there's some loss there, I have a lot of caulking to do between the storm and vinyl windows. It seems almost impossible to stop the infiltration without opening the walls up. I was suprised though when we were told our home was tighter than a newly built 3,000 sq ft home down the road. Still they rated our home drafty like a barn. There's a heat loss calculator on build it solar? That's the calculator we used, and based on our wood furnace's ratings and outdoor temps, it seemed about right. I love our old home, but boy are they a pain.

I have to add, is the second floor 1700 sqft also? If that's the case then your numbers seem more accurate.

 

[Thom Griffin]

Yes, the second floor is also 1770 s.f. Unheated, but 6" insulated 2nd floor was not offered as a choice for a "ceiling" on the slant/fin calculator, so I sort of winged it. I, too, need to do some serious caulking. (My retirement list is getting way too long.) Mostly staying ahead on dry wood solves most problems. I had injured my back last spring and so I just had to buy my first tank of oil in 5 years. That hurt! I don't know how folks can manage that don't have wood.

 

[laynes69]

Try here and see what comes up. It took me a while to get everything in, but like I say it seems accurate.

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

 

[PassionForFire&Water]

I just did the Slant/Fin heat loss for my home: 1770 sq ft bottom floor, old 1830's house; unheated upstairs, roughly 3 1/2" insulation in walls, uninsulated floor, and 6" of insulation above unheated 2nd floor; lots of windows; all of them low-E double pane, however, field stone foundation, so lots of air infiltration.

After entering all the data, the software says the heat loss is 83,451 Btu/hr figured at 0 F outdoor temp and 70 indoors.

Does this seem at all correct? I'm mostly doing this to change a few radiators and balance the heat a bit better. I'm just curious, as the loss seems rather low to me.

Based on oil / propane / wood consumption per year, location (town/city) and heating degree days for your location you can calculate your heat load.
If you provide this info I run it for you.

 

[Fred61]

Well...of course draft sealing would be a great idea. Considering that the house is wrapped in Tyvek, then plank sheathing, granted has only 3 1/2 " of insulation (my wife wanted to be able to see the posts and beams...), and then a plastic vapor wrap and wallboard with a skim coat of real plaster. It's surprising to me just how much air infiltration there is. As I said in my original post, the house has a field stone foundation, so the house "moves" a bit, hence the leakage around the fancy windows. Last year I put up good old triple track aluminum storms and they helped a lot. I just need to do the other half of the house.

There's not much room for any more insulation. As long as it's not windy my Tarm stays ahead of it quite nicely. I just wanted to balance the heat a bit better, and was curious as to my Btu/hr totals.

If you took the place down that far and it's post and beam then insulated panels from Winter Panel in Brattleboro probably would have been a better choice and would have satisfied mother.
http://www.winterpanel.com/

 

[ihookem]

I don't think the BTU rating is off by much. Old houses are drafty. I don't know where you live but when I had enough snow on the ground I would push it up against the house. I have brick but it still helped a lot. Push up snow 3' high if you can, this will keep a lot of draft from getting in to the basement or crawl space. This will keep the floor warmer. A warm floor helps a lot. Don't bother taking the siding off just to replace the sheathing. You will never get your money back.. If you ever reside then go over the sheathing with foam sheathing. I would go in the basement an look for light through the cracks and foam them up wit the chep stuff if not too many cracks. Is your attic insulated??? 2' of cellulose is not out of the question. It does little to keep out drafts but helps a lot when there is no wind. If you ever add insulation in the walls foam in better than anything, packed cellulose is second and fiberglass all out sucks unless you caulk all around the cavity in the wall. Also, it sounds like you replaced windows. Good, but most windows don't really get replaced, just the sashes do with a plastic window replacement package. This doesn't insulate between the window frame and the studs. Many window companies brag that their windows have this R value, or that light transmission but never take off the window casing to foam between the window frame and the 2X4.

 

[flyingcow]

Grif, where are you located?

 

[DBoon]

Quick reality check - what is the BTU/hour output rating on your furnace/boiler right now, and roughly how many hours/day does that run at 0 degrees F?

More than likely, I would guess that this calculation is off by a factor of 1.5 to 2x or so.

 

[Vizsla]

I just did the Slant/Fin heat loss for my home: 1770 sq ft bottom floor, old 1830's house; unheated upstairs, roughly 3 1/2" insulation in walls, uninsulated floor, and 6" of insulation above unheated 2nd floor; lots of windows; all of them low-E double pane, however, field stone foundation, so lots of air infiltration.

After entering all the data, the software says the heat loss is 83,451 Btu/hr figured at 0 F outdoor temp and 70 indoors.

Does this seem at all correct? I'm mostly doing this to change a few radiators and balance the heat a bit better. I'm just curious, as the loss seems rather low to me.

What have you used in previous years for fuel consumption?

For example a similar house with 78,830 btu loss used 263.6 MCF natural gas = 263,600,000 BTU not adjusted for elevation of 800'. Now this heat loss was calculated with a lot of unseen insulation, not as accurate as doing a new construction where you know all the materials being used. But I would say within 5% or less! at a design of 0 degrees also. That gas usage did also include a dryer, gas stove and cooktop. So minus that to give you a rough idea. I'd have to look up heat degree days to get a better idea as well.

 

[Seasoned Oak]

IF this is correct then an average 100,000 BTU gas furnace would run 24/7 at 83% eff to keep up with heat loss. Seems about right at 0 degrees in a poor insulated space. My furnace runs 24/7 when its 0 degrees outside. Its rated at 94000 BTUs