As noted I started keeping track of my coal usage this past weekend.
We've had cold weather where I live in Northern New York.
I've had the coaltrol set at 62 degrees all season.
But since last Friday the temperature has been below that.
So the stove has been running full steam 24/7 since than.
Based on measurements so far I estimate that I use 60lbs of coal a day under these circumstances.
Based on what I have read coal has a maximum BTU potential of 15,000 a pound. This is being generous since most info indicates more like 13,000 btu.
The math as I see it is:
60 x 15,000 = 900,000 btu's a day.
900,000 btus per day/24 hours per day = 37,500 but input per hour.
This is substantially different than the 90,000 BTU's per hour advertised.
Also based on initial measurements I doubt very much that the efficiency is 80%.
My ashes were at least 25% by weight over the last weekend.
Since I assume that 14% is about average, that additional 11% represents a heat loss of about 13%. (11/86).
Assuming 100% of the heat from the burned coal was captured that would represent 87% efficiency.
I don't know much goes up the chimney but I suspect a fair amount - more than 7%.
But for the heck of it let's just suppose overall efficiency is 80%.
(I think it's probably more like 60 to 70%.)
.8*37,500 = 30,000 output.
This explains why I can't heat my house.
Which doesn't make me very happy.
I still save money over oil using coal.
Even if I figure 60% efficiency, the cost is 75% that of oil where I live.
(That's figuring oil at 83% efficiency.)
I figure it costs about $2300 a year to heat my house with oil, if I am heating all rooms to 68-70 degrees.
That's a saving of $600.
However last year I worked long hours away from home and used only about half that so my savings would have been more like $300.
I paid $245 a ton for coal where I live.
The savings would be more or less for others depending on how much they pay for coal.
And also if coal is more efficient than I am estimating.
(I would bet that old style hand fired stoves are more efficient.)
It seems to me that most people are happy with their purchase of their coal stove whatever model or make.
It also seems to me that a number are in the exact same position I am.
I.e. they bought a product advertised as having a 90,000 input which clearly is less than that based on their usage - although they may not realize it.
I think the explanation for this is that for a well insulated house it takes a lot less BTU's than one would think to heat the house.
There are a number of supporting reasons why I think the above must be true - i.e. the total heat input is at best 37,500 btus.
For example I have looked at the fire chamber of my 105,000 btu input oil furnace when the burner is running.
The whole chamber is filled with flame.
Yet in the coal stove there is only maybe an 8" by 2" by 4" bed of coals putting out relatively small flames.
Obviously there is also radiant heat coming of the coals, but that's true of the flames in the oil burner.
I could make more comparisons but when you think about and compare different heating appliances in a similar manner, I think 30,000 to 40.000 btu input seems about right.
Also as I noted before my oil burner could handle minus 30 degree temperatures heating the whole 1st floor to 70 degrees.
I think the coal stove could maintain 62 degrees heating half of the first floor to that and the rest to about 50 degrees, if the average temp were 10 degrees. (50+62/2=56 average temp).
46 degrees of temp difference vs 100 degrees.
Figure older oil burner at 80% efficiency (probably high) = .8 x 104=
83,000 btus output.
Figure coal at .46x83,000=38,000 btus.
Any comments on this?