Is My Math Here Correct?

Is My Math Here Correct?

PostBy: rschoensta On: Tue. Jan. 30, 2007 8:24 am

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?

Re: Is My Math Here Correct?

PostBy: LsFarm On: Tue. Jan. 30, 2007 10:42 am

I don't know what flavor stove you have, but if you have a coal trol on it it must be a stoker. If you have an 8" wide grate on the stoker firebed, and only have a 2" high, by 4" long by 8" wide fire you are not getting the stoker to put out enough coal.

On my LeisureLine Hyfire 1 that I had running in the shop, the bigger burner is about 8" wide, and I had a full bed of fire, about 8"x8" about 2" deep, with 8-10" flames. So you are not getting but half the square inches of burn area, and about half the capacity of the burner.

I'd double check the settings, make sure the stoker pusher or shovel is not jamming on a oversize chunk of coal, and is making a full stroke.

Something is not right. You can set the stoker to push burning coals right off the end of the firebed, and you are nowhere near this from your description.

I'm sure the coal-trol guys will post here soon.

Please post the make, model and flavor of your stove, it will make it easier to follow what is going on.

Take care, and have faith, your unit will make a lot more heat. I was able to heat my shop very easiily with the LeisureLine Hyfire on the small burner alone, only 40K btus.

Greg L
Last edited by LsFarm on Mon. Feb. 05, 2007 11:01 pm, edited 1 time in total.
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Is My Math Here Correct?

PostBy: pvolcko On: Tue. Jan. 30, 2007 8:23 pm

I tend to agree with LsFarm's comments. Could be too low of a max feed rate.

Go into the setup menu (press and hold the menu button for 2 seconds), then move to the "MAX" item by pressing the menu button a few times (can't remember the exact number offhand). When the Coal-Trol Digital thermostat is showing this MAX setting the feeder will run at the speed indicated. Leave it there for 20-30 minutes or so to let the stove get up to and even out that max feed rate burn. There should be burning coals visible up to about 1.5 inches from the front end of the grate, and then coal ash for that last 1.5 inches. Increase the MAX setting up a couple steps and let it run at that for another 15-20 minutes. Continue adjusting until you get the fire covering the grate as described.

Do not leave the stove unattended for very long when running in this MAX setup item. The convection fan might not run and the stove can overheat. If you need to stop adjusting for a while or if the fan is not running and you think it is getting too hot go back into normal running mode for an hour or so to let it cool down before starting the adjustment procedure again. Alternatively, while you are making MAX feedrate adjustments you can unplug the convection fan from the Coal-Trol Digital and plug it into a wall outlet. This will make sure the stove won't overheat while making these adjustments.

We recently discovered this issue and it is being fixed currently. It only affects when using the MAX setup item for max feedrate adjustment.

Usually the default MIN and MAX that the Coal-Trol Digital is shipped with on the Leisure Line stoves is correct, but differences in the construction of the feeder plate or the rotating pusher arm or other mechnical issues can result in those defaults being too high or too low in some cases.