How Much Coal/Hour?

How Much Coal/Hour?

PostBy: Daryn On: Fri Feb 09, 2007 12:23 am

I have a 90K BTU Keystoker and the maximum amount of coal per hour that my stoker consumes is about 4.5 lbs/hour with feed adjustment at maximum. At 12,000 BTU/lb I would expect it to burn closer to 7.5lb/hour.

The recent sub zero temps in NY made me max out the feedrate on the stoker and it has occurred to me that I can't get the necessary amount of coal to the grate to acheive 90K BTU (input). According to my programmable thermostat it has been calling for heat about 16-20 hours a day the last week or so. So far it has kept house at setpoint but I doubt it if the temps go to -10F or if its windy and 0F.

The thermometer on side of stove stays around 625F and on flue above barometric damper around 160F when maxed out. I set draft with manometer per manual at .03

I can't imagine the heat this would put out if it burned 50% more.

How much coal do other 90K stokers consume per/hour? I am using about 70-80 lbs a day to heat 500 ft^2 downstairs and 2100 ft^2 upstairs with high 14.5ft ceiling in living room.

Any feedback would be appreciated.

PostBy: LsFarm On: Fri Feb 09, 2007 12:36 am

HI Daryn, how much of the grate or burning surface of the stoker is covered with redhot coals?? If you get too much coal feed, you will start pushing burning coal off the end of the grate into the ashpan.

Take a look at the burning bed of coal on the stoker, if you have only an inch or so of ash at the end of the grate you are pretty much maxed out. If you have only half the grate covered with burning coal, and your feed adjustment is at max stroke, you may need to make sure the pusher block doesn't have a buildup of fines or dried 'coal-mud' reducing the amount of coal it can pick up and push onto the grate.

With the sides of your stove at 600*+, you might consider an addtional fan blowing on the stove to wash some of the heat off the sides. When I had a wood stove several years ago, I had a small 10-12" oscilating fan that I used to circulate air over the stove body, It was quiet and effective.

Welcome to the forum!! Greg L

Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: WNY On: Fri Feb 09, 2007 11:43 am

keystoker 90K also.

If I turn my feed rate up, I end up pushing hot coals off the end of the plate, I use the factory 2 turns and sometimes back it down to 2-1/2 to 3 turns. it usually doesn't stay where I set it, I have to check it every other day or so to make sure it hasn't backed out. You should have 3/4-1" of ash at the end from what I was told.

I am only running 400-500 degrees on the sides, I have never seen much over 500 on the cheapo magnetic thermometer.

Probably 50-60#/day roughly. I would think full adjustment would be in your range 80#/day.

I have seen the exhaust get upwards of 250-270 without a baro damper, I didn't want to push it any farther than that.

Being in the basement, I have been running it hotter than normal, but only taking the chill off the first floor running almost full time lately, plus being so cold, it will draw and burn more.
Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

PostBy: BigBarney On: Fri Feb 09, 2007 1:02 pm

As 90000 btu input stoker if run at full output I calculated it would have to

burn 7.5# of coal per day.

24Hour x 90000 btu input = 2,160,000btu used per 24 Hour

2,160,000 btu / 12000 btu # = 180 # coal burned.

To put out 90000# btu/hr you have to burn the 7.5 # that Daryn had in

his post. 90000btu/12000btu# = 7.5

How much coal can this stoker burn per hour at the maximum feed rate

with out unburned coal falling off the grate?

Ted BigBarney

PostBy: Yanche On: Fri Feb 09, 2007 5:02 pm

For my AHS S-130 130,000 BTU/hr. boiler the combustion efficiency is 84%.

So, with quality anthracite coal at 14,876 BTU/lb analysis.

130,000 BTU/hr divided by 14,876 BTU/lb all divided by 0.84 results in 10.4 lbs/hour for full output.

On a very cold day and night I burn approximately 100-110 lbs. Per hour average would be 110/24 = 4.6 lbs/hr. Less than half the capacity of the boiler.

The coal hopper holds 400 lbs, I could run 3.6 days (400 lbs divided by 110 lbs/day = 3.6) without adding coal. But my ash bucket capacity is less that three days worth. 400 lbs of coal would produce 400 X .188 = 75.2 lbs of ash. To much volume for my ash tub. Numbers, numbers Engineers like numbers! :-)

Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

PostBy: BigBarney On: Fri Feb 09, 2007 6:14 pm


The 14876btu/# is probably the gross output of your coal dry and ash free.

Since you have 18.8% ash,moisture and non burnable minerals, you

have to subtract the 18.8% of non heat producing weight in the coal.

So 14876btu/# - 18.8% = 1487- 2797= 12079 ash free btu/#

Then burning at 84% efficiency you get 12079 x .84 =10146 btu/#

So for full output you need to burn 12.81#/hour then potentially you

would burn 307#/day. Very seldom would you be able to run at full

output for 24 hours steady so your use would be between 0-307#.

At 100-110#/day or 1,014,600btu/day.

This is a very efficient boiler and near the top end for solid fuel


BigBarney Ted

Keystoker 90 heat output

PostBy: brent14133 On: Fri Feb 09, 2007 8:33 pm

Hello all - First time poster here, and first year Keystoker 90 user. And a cold one, too.

My keystoker just doesn't seem to be putting out the heat. The convection fan cycles on and off, indicating to me that either: A) the fan's cooling capacity is much higher than the stove's heat output, or B) the stove is not putting out nearly its rated 90 KBTU/hr. My vote is B.

My coal use is 40 - 50 lbs/day, and with the calculations noted above, that averages out to 25 KBTU/hr. That's consistent with the fan cycling. That said. the red hot coals extend to the end of the grate. Seems like more feed rate will just push burning coal into the ash pan.

Any thoughts for more heat?

Many thanks!!

PostBy: WNY On: Fri Feb 09, 2007 8:53 pm

Check your draft, you may be loosing heat up your chimney. Do you know what your exhaust temp it? Is your a Bottom or Top Exhaust vent? Mine vents out the bottom, keeping most of the heat in the stove, I converted mine from a Direct/Power Vent to our chimney when we moved.
How close is your thermostat, if it satisfies it quickly, the stove will cool down/heat up and cycle the fan on/off.

These stoves radiate alot of heat on the sides, the fan only takes the heat from the back and top of the stove. They should make heat exchangers for the sides to capture more of the heat.

Your convection blower should be 265cfm, there is a Black Box on the side that you can take the cover off and change the HI/LOW setpoints on the fan. There is a probe that extends into the air path and rotates as it gets hot tripping the fan.

There are 3 Tabs on the circle.

1. TOP tab around 200 Degrees is your HI LIMIT SWITCH, if the blower fails or your stove REALLY gets cranking and it can't cool it, it will stop the stoker. I have never seen mine over the Fan On limit of 160.

2. HI Temp Fan ON

3. Low Temp Fan Off.

Yes, mine cycles on/off depending on the stove temp. It cools the back/top of the stove nicely and trips off.

I moved the lower point down a bit and kept playing until it stays on when the stove is around 400+ degrees, and on cold nights, it runs most of the time.

I think the factory setting is 110 off and 160 on? I think I have mine at 150 on and 90-100 off...
Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

PostBy: brent14133 On: Fri Feb 09, 2007 10:26 pm

Thanks WNY!! I'll follow your suggestions.

I'm not sure what my draft is, nor what the exhaust temp is. I have the hearth version of the stove so the venting is unaccessible for me, but it is a bottom vent. It did cross my mind that I might be sending too many BTU's up the chimney (30 feet of stainless liner - probably draws a big draft). How do I check the draft? What's the proper amount?

Also, the coal consumption numbers don't seem to work out. 90KBTU/hr x 1 lb/12 KBTU x 24 hr/day = 180 lbs/day. I'm barely burning 50 lbs/day and the grate is full of red coals all day. There's just no way this stove can push 180 lbs per day without sending unburned coal into the ash pan.

I'm coming to believe that 90 KBTU/hr would heat my house nicely, but that my 90 KBTU/hr stove really can only make about 25 KBTU/hr at full tilt. Or, the more likely scenario...I'm missing something obvious.

PostBy: LsFarm On: Fri Feb 09, 2007 10:55 pm

HI Brent, welcome to the forum. If the grate is full of red coals it's full length, then the burner is making it's max heat.. I think Dave has it right, you are losing a lot of heat up the chimney.

You need to figure out a way to put a damper on the chimney to cut back the draft.

Greg L
Last edited by LsFarm on Sun Feb 11, 2007 12:59 am, 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

PostBy: Yanche On: Sat Feb 10, 2007 12:20 am

BigBarney wrote:Yanche:

The 14876btu/# is probably the gross output of your coal dry and ash free.

I got the specs from one of the PA coal brokers. Here's all of the numbers:
"Nut coal dry specs:

Moisture: 5.49% (as received)
Ash: 9.58%
Sulfur: .59%
BTU/lb: 13,451
BTU/lb: 14,876 (dry, ash-free)
Volatile Matter: 4.36%
Fixed Carbon: 95.17% (dry, ash-free)
Ash Fusion Temp: 2,700 F
Lbs sulfur per million BTU's: 0.44

Coal analysis report by GeoChemical Testing Somerset, PA. "

Should I have used the lower number 13,451 BTU/hr? In general how do I use these numbers? For example does 9.58% ash mean for 100 lbs of raw coal I will get 9.58 lbs of ash? 100 lbs of raw coal yield 0.59 lbs of sulfur? Does 0.44 lbs of sulfur mean sulfur in the combustion gas after a million BTU's have be burned? Questions, questions? What kind of book would I look for to understand what this all means?

Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

PostBy: BigBarney On: Sat Feb 10, 2007 1:15 am


You do get 9.58# of ash/100# of coal and 5.49#of water and .59# of


The btu figure they give is the dry ash free coal 14876 btu - only the

ash 14876 x 0.0958 = -1425 = 13451 btu/#.

You may also see a MAF amount which also takes out the moisture and

the ash, Moisture Ash Free btu.

Most stokers cannot get much of the volatiles to burn because of no

secondary air for combustion,so a portion of these are also useless.

So if the 14876 btu coal has the ash 1425btu,water 817btu,sulfer 88btu,

volatiles 649btu subtracted, you get 11897btu/#.This is the actual heat

value of this coal,maybe a little more if some of the volatiles combust.

Here is the WIKI for coal and has many definitions and added info on

all types of coal from the mine to the burning.

Ted BigBarney

PostBy: Daryn On: Sat Feb 10, 2007 4:42 pm

Greg, hot coals go right near end of grate (about 1"). My fire is maxed out and no way is this a 90K BTU stoker. I couldn't burn any more coal or I would be wasting it by pushing unburnt coal off end of grate. I would really like to know how they came up with the 90K BTU rating.

I got it with the optional 6" hole cut in top and the larger 350 cfm blower installed. That works great...heat coming out upstairs is 160F. My stairway leading upstairs is all open and you can feel the cool air going down......make for a nice natural cool air return.

I called Keystoker and person I talked with could not tell me what max feed rate was.

Can anyone who owns a 90K BTU Leisure Line, Harmon or Alaska comment on their max feed/heat output?


PostBy: LsFarm On: Sat Feb 10, 2007 6:59 pm

Hi Daryn, I'm running a LL pioneer model in the shop right now. It is rated at 85 or 90K. I have the firebed about 1/3 to 1/2 covered with hot coals. and I'm burning a 5-gallon bucket every 12 hours.. I've been told a 5 gal. bucket is about 35#, and that seems to be accurate. I tried to put a whole 40# bag of rice in a bucket and it wouldn't all fit.

So I'm burning about 70-maybe 80# per day, I think if I ran it at max with a full bed of hot coals, it would be about another bucket per day. so lets say 120#.

I do think these stoker stoves do put out 85-90K of heat. But where the stove is located in the house incredibly important. the basement is not a great place for heating effeciency. All the radiant heat from the sides of the stove is lost heating the basement, and I'm going to estimate that this is about 30-40% of the stove's ouput.

If you want to increase the heat upstairs, put in a cold air return duct, even just a dryer vent hose attached to the inlet of one of your distribution fans with the hose taking air from somewhere upstairs will net you a huge increase in heat.

Take a look at this thread:

Give it a try. Insead of using the stairway as the cold air return. I think you will be amazed.

Greg L
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

PostBy: brent14133 On: Sun Feb 11, 2007 12:32 am

Hi Daryn - I'm a Keystoker 90K owner, too, and like you, I'm coming to believe that the 90KBTU/hr number is way too big for the heat these things put out. The math just doesn't work out (see my post above.) Maxed out, my 90K pushes about 70 lbs/day and at that rate the bed is full of red coals, there's a big 16 inch flame shooting into the firebox.....and there's some unburned coal in the ash pan. It just won't burn coal any faster than that.

Simply based on coal consumption rate, the energy input into the firebox is way below 90KBU/hr. If you take my 70 lbs/day, you get......

70 lbs/day x 12 KBTU/lb x 1 day/24 hrs = 35 KBTU/hr, not the advertised 90 KBTU/hr.

Subtract efficiency and heat transfer losses from that, and the amount of heat actually getting into the house is likely in the 20 KBTU/hr rate at full tilt.

I'd love to see Keystoker's calculations. I bet they don't add up.