Heating Hours and wood consumption

[Como]

We have a load at -10 of 500,000 btu. The nearest comparable location I have found shows 3,500 heating hours.

Just those raw numbers imply about 100 cords, softwood.

There are 3 variables I can think of:

It is of course not -10 all that time, now it can go lower, but the average is higher.
We do have a fair bit of passive solar gain.
We have significant wind chill.

I am sort of assuming the latter two cancel each other, but is there a rough and ready allowance to reduce the max load? I was thinking of just dividing it by 2. I have no historical data for fuel consumption that is of any practical use.

I was thinking of diving by 2, 50 Cords, and then taking a bit off as we will not be heating the building to 65 all the time.

 

[DaveBP]

Siegenthaler gives a method for estimating the annual heating energy total for a building in his "Modern Hydronic Heating":

The total in million BTUs is equal to the design heating load in BTUs/hr X the annual total heating degree days at the site X 24 X a fudge factor that looks like about .66 for your location and all of that divided by one million times the temperature difference at which the design load was calculated which would be 65F - (-10) = 75 degrees for the temps you indicate you used.

Remember though, air infiltration is a real bugaboo in all these sorts of estimates and can be as large or larger than the conduction heat losses. I think taking the max load and halving it for an average is safe. Solar gain is another world again.

 

[sgschwend]

Were you asking a question?

I am guessing you meant to suggest a load per hour or is that per day?

The heat loss calculation is a linear one so the load would double if the delta T is doubled, therefore you load would be half as big at half the delta T. Somewhere around 25-30 degrees F. the load should be half as big.

 

[Nofossil]

We need more units here. Is that 500,000 BTU per hour or per day?

500,000 BTU per hour is hard to believe unless you're heating a sports arena. Our 3500 square foot house needs about 40,000 BTU per hour at -30, and it's not anywhere near state of the art in terms of insulation or glazing.

 

[SE Iowa]

Yes, my average winter day's consumption of NG is 500,000 for 4600sf in Iowa. Our climate is similar to yours unless your in eastern Colorado where it is more windy. 50 cords seems exceptionally large. My friend burns 16-20 cords per year in an inefficient OWB and keeps his 80 yo farm house on top of a hill with no wind protection at 75-76F all winter.

 

[Nofossil]

I'll believe 500,000 BTU/day - that's pretty close to my average load. I use about 4 cords a year (replacing 600+ gallons of fuel oil).

 

[Como]

500,000 an hour, 100 per sq ft give or take.

So 4 cords x 24 is about 100.

My calc was that assuming 100 cords at full load, a reasonable figure would be 50 cords for the heating season. Might be down to 35 cords with keeping the buildng at 45F during Jan/Feb.

35 Cords cost roughly

$5,000 for wood (Pine/Aspen)
$6,000 for pellet
$12,000 for Electricty
$20,000 for Propane.

Wood is the only one I have any control over.

So wood needs to be the primary source, pellets as back up and/or top up.

 

[flyingcow]

Durango,
You have a greenhouse operation or something like that don't you?

 

[Como]

5500 sq ft

But solid brick walls, high ceilings and at 10,000ft, an old railroad hotel.

 

[deerefanatic]

Holy Cow!! Is there the possible option in the future to put a few inches of spray on insulation inside, then put like a fake-brick interior inside so as to get some insulation? Same with roof? or when the next time comes to re-roof, pull out any insulation and put in spray foam? (I say spray foam because it has such a hi r-value per inch)

 

[Como]

Solid brick with plaster onto brick inside, not practical to frame etc and insulate.

Roof will be insulated to R60

Foundation wil be insulated.

Double pane storm windows will be installed

We will be using some spray, a thin coating more to seal, too much and you pop the lathe and plaster. Loose fill on top, we have plenty of space in the attics.