# Is Heat Output Linear in a Stove Using a Coal-Trol?

### Is Heat Output Linear in a Stove Using a Coal-Trol?

Is heat output linear in a stove using a Coal-Trol? I have a LL Pocono, 110000 BTU, max
feed rate 40, min 6. 110,000 ÷ 40 = 2750 BTU's at a feed rate of 1, 27,500 BTUs at 10. I
understand stack temps go up as the feed rate increases so I suppose a little is lost there
but is there more to it than that?
Turbogeno

Hot Air Coal Stoker Stove: LL Pocono
Hand Fed Coal Stove: VC Vigilant II at home and a military surplus tent heater at camp
Coal Size/Type: Anthracite, Rice and Nut
Other Heating: Oil hot water baseboard and DHW

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

I would suggest that to determine this (with no fire going) you measure (weigh) the anthracite being pushed off the stoker ramp per unit of time for three of the available feed rate settings, spanning low, medium, and high feeds. All of the heat you can possibly get delivered into the home resides in the coal to begin with.

The input BTU's are calculated as follows:

Lbs. anthracite feeding per hour x 12,300 BTU's/Lb. = BTUH input

I would then multiply the results by 0.75 to get a reasonable approximation of BTUH output.

Bag the coal coming off the stoker and take it to the post office or UPS or Fed-EX and have them weigh it on a postal scale for high precision. Or alternately, you most likely have one of these high precision small package shipping scales where you work. Zero the scale first after placing an identical bag onto it, so the bag does not enter into the calculations.
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

That works, excellent idea.
Edit, addition; I just need to make sure I lock in my selected feed rate. I should be able to do that by setting the t-stat real high and waiting for the feed rate to go to 100.
Turbogeno

Hot Air Coal Stoker Stove: LL Pocono
Hand Fed Coal Stove: VC Vigilant II at home and a military surplus tent heater at camp
Coal Size/Type: Anthracite, Rice and Nut
Other Heating: Oil hot water baseboard and DHW

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

Turbogeno wrote:That works, excellent idea.
Edit, addition; I just need to make sure I lock in my selected feed rate. I should be able to do that by setting the t-stat real high and waiting for the feed rate to go to 100.

Here is how to fix the max @ feed rate 100% during Larry's excellent test. This is how my stove is run 24-7. Provides a heat soak effect with easily predicted fuel use and quick push button adjustment for nighttime temps.

Coal-trol on feed rate

I'm amazed at the innovation on this forum to accurately access these sort of questions.
Uglysquirrel

Stove/Furnace Model: Pocono

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

Uglysquirrel wrote:I'm amazed at the innovation on this forum to accurately access these sort of questions.

Agreed and leaving max displayed at a 40 feed rate keeps it feeding at 40. (45 seconds out of 120)

I should run the test again but it seems the 110,000 BTU rating is with the feed motor running all the time.

I have an old triple beam scale and got 4.18 lbs in an hour at 40, 51414 total BTUs -25% gets me 38560 BTUs of heat out of the stove. I'm not sure what the thermal efficiency of modern stokers is but I think the combustion efficiency is 80-90%

At 20 I get 2.15 lbs. in an hour, 26445 total BTUs -25% gets me 19833 BTUs of heat out of the stove.

A 10 I get 1 lb. in an hour, 12300 total BTUs -25% gets me 9225 BTUs of heat out of the stove.
Turbogeno

Hot Air Coal Stoker Stove: LL Pocono
Hand Fed Coal Stove: VC Vigilant II at home and a military surplus tent heater at camp
Coal Size/Type: Anthracite, Rice and Nut
Other Heating: Oil hot water baseboard and DHW

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

The heat output seems to be linear.
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

It will be roughly linear, however, keep in mind that MIN establishes an offset in your calculations:

So if 40 is MAX and it is equal to 52KBTU by your measurements then that means 1.3KBTU per point of MIN/MAX. MIN of 6 means 7.8KBTU is your low floor.

Then you figure out what each point of FR means: 52 - 7.8 / 100 = .44 KBTU per point of FR with 0 being 7.8KBTU and 99/100 being 52KBTU.

There will be variances. For instance at high feeds you may get a "stacking" effect on the grate where the coal bed gets deeper than at low feeds, resulting in some skewing.
pvolcko

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

OMG, metrics. You will notice up to around MAX=15 the ash has no black lumps but as you increase the heat some unburnt coal appears (I assume it is unburnt coal) and stacking does occur making the fire less intense. So I assume efficiency drops off a bit. So the CN mantra says, run anything at half to 2/3rds capacity max and if you need more you should have bought a bigger stove or got more than one. So measuring coal pushed out is but one measure of heat output.
coalnewbie

Hot Air Coal Stoker Stove: LL AnthraKing 180K, Pocono110K,KStokr 90K, DVC
Hand Fed Coal Stove: Invader 2
Baseburners & Antiques: Wings Best, Glenwood #8(x2) Herald 116x
Coal Size/Type: Rice,
Other Heating: Heating Oil CH, Toyotomi OM 22

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

What the hell is a linear????????
freetown fred

Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

freetown fred wrote:What the hell is a linear????????

Fred, just think of it as being well behaved.
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

My pounds per hour test in a cold stove goes way out the window when the stove is burning. I guess it's a lot easier to push ashes off the grate than unburnt coal. At a fixed feed rate of 9 the stove burns +/- 50 pounds a day and keeps the house comfortable down into the single digits. It was a 48 hour test. I had both the minimum and maximum feed rates at 9 during the test.
Turbogeno

Hot Air Coal Stoker Stove: LL Pocono
Hand Fed Coal Stove: VC Vigilant II at home and a military surplus tent heater at camp
Coal Size/Type: Anthracite, Rice and Nut
Other Heating: Oil hot water baseboard and DHW

### Re: Is Heat Output Linear in a Stove Using a Coal-Trol?

Another way is to top off the coal box and run a constant MAX feed rate for a day or so, level out the coal and measure the depth of coal use. From there you get a volume with a lb/hr being calculated , first need to weight a certain coal volume one time reference for all testing.
Uglysquirrel

Stove/Furnace Model: Pocono