Maximizing Efficiency of Your Hand Fed Appliance

I'm sure many of you have found little tweaks to make your hand fed appliance more efficient. I thought it would be cool to have a thread packed with these discoveries.. These stipulations would pertain mainly to Anthracite. I have a hand fed furnace. This is what I've learned so far.....

Combustion Air
More primary air entering the firebox = more heat being produced. Its important to have just the right balance of combustion air, since secondary air can just carry heat up the chimney. Primary air must be forced to travel up thru the coal bed and not have any other option, no way to bypass the coal bed, so that all its available oxygen can be used. I've found that best efficiency is achieved when there is sufficient air coming in under the grates and just a smidge of air over the fire to burn up gases off the top. Which leads to my next topic -

Draft
Draft is a big one. Just the right amount of negative pressure in the firebox. On my Clayton it seems to be around a .03" WC. Too much draft will pull heat thru the firebox too fast. Too little draft, not enough combustion air gets in for combustion. Proper use of barometric dampers and manual dampers help regulate these. We want the heat to spend as much time in the fire box as possible so it can be transfered outside the firebox before exiting the chimney. Which brings me to the next topic -

Heat Transfer
Heres one that took me a little while to stumble on to. Between the fire and the heat we feel is a steel wall. I've found that keeping the inside of the firebox clean by brushing ash off it once a week, greatly improves heat transfer from the fire to where I need it to be. This includes the build up of ash in the firebed itself. This is a big factor for us owners of the V shaped firebox.. More ash along the sides of the coal bed insulates heat transfer to the bricks, ultimately slowing heat transfer thru the steel and cuts down the surface area where heat is being transfered. Which means I should shut down and clean out a little more often than I do...

Surface Area for Heat Transfer
More surface area for heat transfer = more heat is transfered. I assume thats why some appliances have tubes of moving air or water in the firebox. Tubes greatly increase surface area for heat transfer. Mine has no tubes, I've considered adding some.

I've found a simple way to increase surface area for heat transfer. I leave the ash pan out between shake downs. In the picture below, heat is radiated downward heating the bottom of the ash pan area. Directly underneath that, there is two inches of space where the blowers are sending in air to get heated and be sent thru the duct work.. I've noticed a substantail amount of more heat doing this, mainly in the first half of a 12 hour burn, when that heat is cascading down onto the floor of the ash pan area.

And what about flue pipe heat transfer to the room? A foot out from the furnace the pipe is 180 degrees. I have at least 10 feet of flue pipe in my basement before it gets to the chimney. Right where it enters the chimney, I can lay my hand on the pipe and its comfortably warm. So if this is all the heat thats left from my burning mass of coal thats finally going up the chimney, How efficient is my heat capture totally? 80%? More? I'd love to hear your opinion

You made a good argument for leaving out the ash pan between shakes. I'm gonna try this and see if I notice anything, but it makes sense.

Lightning wrote: How efficient is my heat capture totally? 80%? More? I'd love to hear your opinion

Nice topic and a great picture of your grate. You must be proud to have gotten it that even.

It's not easy to determine overall efficiency. You can infer combustion efficiency by measuring flue gas temperature and CO2 and CO percentage, but this will not give overall efficiency and would change over the course of the burn. Once you knew average combustion efficiency and flue gas temp. and BTU content of the coal you were using and how much you could probably get pretty close.

Years ago Consumer Reports measured the output of a number of kerosene heaters. Most put out less than they were rated at. They did it by using a sealed room with measured cubic foot per minute air in and out and measured the rise in temperature of the out air from the in air. Knowing the BTU content of the kerosene and amount consumed they could have determined the efficiency as well. So it gets kind of involved.

franco b wrote:Nice topic and a great picture of your grate. You must be proud to have gotten it that even.

Hey thanks Franco! I do strive to clear that grate as good as I can so that I get a consistent 12 hour burn time between shakes and re loads. Actually, I have a couple tools that I bent up out of steel rod and some angle bracket material that I poke and slice from under the grates to get as much ash out of the way as possible. Since this grate system is handicapped just by its design, this is how I manage the even glow radiating down thru the grates that you see in the pic

Lightning wrote:So if this is all the heat thats left from my burning mass of coal thats finally going up the chimney, How efficient is my heat capture totally? 80%? More?

franco b wrote:It's not easy to determine overall efficiency.

As for efficiency, I was meaning it in a simpler sense. For example, If my fire is generating 10,000 BTU How many of them am I losing up the chimney, since my pipe is only comfortably warm before it enters the chimney?

EarthWindandFire wrote:You made a good argument for leaving out the ash pan between shakes. I'm gonna try this and see if I notice anything, but it makes sense.

Yeah, I figure the ash pan is just blocking that radiated heat from warming the floor of the ash pan area

Thank you both for the replies

Great post.

I will have to try to employ some of these tactics. I do not have an ash pan, my ash just falls into the pit below the grates. and i am currently expirementing with over fire draft to determine the sweet spot.

Lightning wrote:As for efficiency, I was meaning it in a simpler sense. For example, If my fire is generating 10,000 BTU How many of them am I losing up the chimney, since my pipe is only comfortably warm before it enters the chimney?

All you can tell is that your stack temperature is not excessive and you do need that heat to maintain draft. You have managed work arounds to keep the fire burning well so that is about as far as you can go without getting into exact measurements.

jpete wrote:My reasoning for leaving my ash pan out between shakings is that the area under the fire is equivalent to your lungs.

Ah yes, perfect an unobstructed pathway for fresh combustion air to get to the underside of the grates!!
Makes good sense to me!!

jpete wrote:And how well do you breath when your lungs are half full of junk?

Not very well. Lung disease ... AND asthma here ...

I don't know - the way I look at it, I've been burning for 7 seasons and have never removed the ashpan during a burn ... so why start now? It works as it is.

But, now I have to try it .... Maybe it'll get the bottom of the stove hotter, and radiate that much more heat into the room? Hmmmmmmmmmm ......

I think those of us with baseburners can't comment on removing the ash pan....

I also use a lot of over the fire air. My stove is quite responsive to over the fire air. I pretty much gauge efficiency by high stove temps and low stack temps...

dj

SMITTY wrote:But, now I have to try it .... Maybe it'll get the bottom of the stove hotter, and radiate that much more heat into the room? Hmmmmmmmmmm ......

Yeah man, you know what I'm talking about Smitty

Boots wrote:Great post.

I will have to try to employ some of these tactics. I do not have an ash pan, my ash just falls into the pit below the grates. and i am currently expirementing with over fire draft to determine the sweet spot.

I've found that just the right amount of over the fire air will help burn gases off the top of the coal bed that would otherwise go up the chimney without yielding any extra BTU's.

Also, on warm days when draft is falling, let an excessive amount of over the fire air in while your primary is cut back to a sliver. Not for combustion purpose, but instead it will just get heated and go up the chimney so the draft won't fail.

i have no control over my primary air. it is a natural draft boiler. I just have a flap with a small hole in it attached to an actuator that opens for high fire. I just recently started running with over fire air. i started at 1 full turn open then i went to 3\4 turn then to 1/2 turn. apparently that was too little over fire air because i got a call at work from my mother- in- law, " i just heard a big boom from the basement". Everything was fine but i went back to 1 turn open for a couple of days just to make sure i corrected the issue. Tonight i put it back to 3\4 turn.

I did notice that prior to me using over fire air my stack temperature was about 150°f. At 1 full turn open it stays at about 200°f. these temps are noted after extended periods of "idle" burning. I cant completely blame the over fire air though. it has been colder out, and i also noticed a slight increase in draft, maybe .01" higher.

Lightning wrote:I've found that keeping the inside of the firebox clean by brushing ash off it once a week, greatly improves heat transfer from the fire to where I need it to be.

That sounds promising. Do you have a long handled wire brush?

Lightning wrote:I have at least 10 feet of flue pipe in my basement before it gets to the chimney.

Some wood burners make a big point of this. Look at some old old pictures of the general store where all the old farts would sit gabbing around the wood stove in the evening, and you see a stovepipe running the whole width of the room. Of course with a wood fire they have higher flue temps to keep the draft going. I will have to re-do my stove pipes next fall, and I'm thinking of putting the baro further away from the stove so I will have a couple feet more of hot radiating pipe. Supposedly the baro should be close to the firebox but I doubt it will hurt the baro's operation.

Also see the thread by 63roundbadge, on attaching heat sinks to the stove
Anyone attach aluminum or steel heat sinks to your stove?