Rob R. wrote:lsayre wrote:Also the cost of the extra 6-8 degrees of round the clock warmth was not initially considered,

That much difference in average temperature is significant.

I just tried to fathom this significance using degree days as follows:

So far for February the average daily temperature around here has been 32.86 deg. F.

Therefore the average daily number of degree days has been 65 - 32.86 = 32.14 degree days per day

I'm burning coal at a rate of about 1.6 lbs per degree day, so 17 days x 32.14 degree days/day x 1.6 = 874 lbs. of coal burned (my actual for Feb. is 866 lbs, so this is close)

Now instead of my home being at 62 degrees, it is at 68, so the difference is 6 degrees. If I assume that it was actually 6 degrees colder outside instead of warmer inside (all things being relative), then the above calculations convert to:

Average temp outside at 6 degrees colder = 26.86 degrees

Therefore the average daily degree days would be 65 - 26.86 = 38.14 degree days per day

At 1.6 lbs. of coal burned per degree day for 17 days I now get: 17 days x 38.14 degree days/day * 1.6 = 1,037 lbs of coal burned

Taking the difference as a percentage I get: [(1,037/874 * 100) - 100] = 18.65%

My conclusion is that it requires 18% to 19% more energy to keep my home at a steady 6 degrees warmer (so it takes about 3% more energy for every degree of extra warmth).

I had initially calculated that I would burn 4 tons of coal, and if I multiply that by 1.1865 I get 4.75 tons. An increase of 3/4 of a ton.

If as I assume, I will burn 1 ton more than I had initially calculated, then fully 3/4 of that extra ton can be explained by the warmer house temperature alone.

That leaves only 1/4 of a ton of extra coal to be blamed on various of the other reasons for lower efficiency, and obviously in reality I'm doing much better than 65% to 70% as to my overall system efficiency.