Harmon Hand Fired Coal Furnace.

A buddy has purchased and installed a 1500 SF. coal/wood furnace. It has the auto draft hooked up to his thermostat. Basically it works great!
The thing is he goes through a lot of coal. Like 100 lbs a day easy and his house isn't all that huge.

How should it be set up to get the best use of his BTU's?

Right now he has the idle open just a bit and when the thermostat calls for heat it automatically opens the air control and stokes the fire up big. Then when the thermostat is satisfied the fire drops back to a slow Idle. So the fire is raging and off... It never really Idles.

I have suggested he set up the furnace to run higher than idle to the point that the furnace heats the house for the most part except on the coldest, or windiest times. Then the thermostat can open the air a bit more to give the little extra. This would IMHO even out the fire and conserve fuel.

What say you all?

Two things to consider.. He says for it to heat the house well the furnace needs to be around 600f. The circulating fan runs when the furnace is at temp.

When it's cold, its not uncommon for any stove to use 60-100#day to keep up. When burning coal, is he using baro damper and have it adjusted correctly? Maybe too much draft.

A fire that is idling or air restricted will generate large amounts of carbon monoxide gas that just goes up the chimney without heating anything while still consuming coal.

Your thought to increase the fire size during idle periods is good, more CO will be burned.

The larger the stove or furnace the more wasteful it will be at low heat outputs.

franco b wrote:A fire that is idling or air restricted will generate large amounts of carbon monoxide gas that just goes up the chimney without heating anything while still consuming coal.

Your thought to increase the fire size during idle periods is good, more CO will be burned.

The larger the stove or furnace the more wasteful it will be at low heat outputs.

That's what I was thinking. The furnace is burning and not generating any heat for the house.

WNY wrote:When it's cold, its not uncommon for any stove to use 60-100#day to keep up. When burning coal, is he using baro damper and have it adjusted correctly? Maybe too much draft.

Oh I don't disagree that one can use coal. I just think he is wasting some of the heat potential. A quick check of the math ...

12500 x 100 = 1,250,000 BTU's of potential. That's like using 10 gallons of fuel oil in an average day... Not an overly cold one. He said he uses more coal when it's real cold.

markviii wrote:Can he adjust how far the air control opens on a heat call?

I'm not real sure about that. It seems to really be flowing because he gets flyash build up (several pounds a season) in his stove pipe where it enters the chimney thimble.

Stanb999 wrote: Right now he has the idle open just a bit and when the thermostat calls for heat it automatically opens the air control and stokes the fire up big. Then when the thermostat is satisfied the fire drops back to a slow Idle. So the fire is raging and off... It never really Idles.

That description sounds like the original designers were thinking fuel oil furnaces... It sounds maybe OK for wood, but not coal. I think you are loosing a lot of heat up the chimney. You've called this a furnace so I'm assuming this runs hot air for heat circulation. I think you need to think of how to take the fundamental design to go from an "on-demand" to a "continuous" heat source. So your suggestion is definitely going in the right direction.

Second is to look at how to keep more heat in the house and not going out the stack...

dj

markviii wrote:

Stanb999 wrote:It seems to really be flowing because he gets flyash build up (several pounds a season) in his stove pipe where it enters the chimney thimble.

Flyash in the stovepipe is part of burning coal, but if you think the amounts are excessive the draft might be a little strong. Has the draft ever been checked? Does he use a baro or manual pipe damper?

Yes he has a baro.

dlj wrote:

Stanb999 wrote: Right now he has the idle open just a bit and when the thermostat calls for heat it automatically opens the air control and stokes the fire up big. Then when the thermostat is satisfied the fire drops back to a slow Idle. So the fire is raging and off... It never really Idles.

That description sounds like the original designers were thinking fuel oil furnaces... It sounds maybe OK for wood, but not coal. I think you are loosing a lot of heat up the chimney. You've called this a furnace so I'm assuming this runs hot air for heat circulation. I think you need to think of how to take the fundamental design to go from an "on-demand" to a "continuous" heat source. So your suggestion is definitely going in the right direction.

Second is to look at how to keep more heat in the house and not going out the stack...

dj

It's a furnace with a plenum that attaches directly to your heat ducts.

I'm kinda thinking the same thing. He's using it like an oil furnace. When I think it should be run in a continuous fashion.

Personally, I really think you are on to something when you say it is being used kind of like an oil furnace, not a coal furnace. Back in the day when coal fired hot air, hot water, and steam boilers were used, the heat source was constant. With hot air in particular, the intensity of the fire determined how much heat got distributed. Probably would be better to establish the fire in such a fashion to run the blower constantly and let the heat distribute. Maybe run it like a manual coal stove.

Some chimneys do not do well with baros. Mine does not for instance. If his chimney really draws well, then there is a lot of cold air being sucked in at the baro. Personally a manual flue damper works much better for me. It keeps more heat in the unit, and less heat wasted up the chimney.

Does your friend have a monometer? If not, he really needs one to know what the actual draw is. He could just be drawing way tooooooo much air.

Bear038 wrote:Personally, I really think you are on to something when you say it is being used kind of like an oil furnace, not a coal furnace. Back in the day when coal fired hot air, hot water, and steam boilers were used, the heat source was constant. With hot air in particular, the intensity of the fire determined how much heat got distributed. Probably would be better to establish the fire in such a fashion to run the blower constantly and let the heat distribute. Maybe run it like a manual coal stove.

Some chimneys do not do well with baros. Mine does not for instance. If his chimney really draws well, then there is a lot of cold air being sucked in at the baro. Personally a manual flue damper works much better for me. It keeps more heat in the unit, and less heat wasted up the chimney.

Does your friend have a monometer? If not, he really needs one to know what the actual draw is. He could just be drawing way tooooooo much air.

Being contrary... the chimney in question doesn't have great draft. I think he gets the build up from the wide open air control when it calls for heat. I believe he has used the monometer to adjust the Baro.

Think of it. The coal bed is all in or idle. No in between. No even burn like a coal fire should be.

Would also be nice to know the stack temperature.