Magnum Combustion fan experiment

I've been trying to figure out what the difference would be between running the combustion blower continuously vs letting it cycle on and off with the Harman controller. The question being, which gives me the better results (most complete burn, best heat output, etc) I burned for several days with the blower running and collected the ashes in a metal barrel, then did the same with the blower cycling on the controller. I kept everything else the same, feed rate, air intake past the restrictor plate, thermostat setting, pilot timer settings (4 on 12 off), etc.
For my results, I asked a disinterested neutral third party (the D.W.) for an opinion, though I had to explain what I was doing when I called her outside to "feel my ash" the first time

Anyhow, she thinks that there's not much difference in the two barrels- the ashes generally look and feel the same, and when you crush them up, they're pretty identical as far as complete burning goes. As for the fire, there was a big difference- with the blower "on", the stove stayed warmer (350) between cycles, but the fire burned back pretty fast to a skinny orange ribbon that took awhile to build back whenever the thermostat kicked in. In pilot mode, the fire never grew beyond that 1.5-2 inch ribbon. The stovepipe stayed warm the whole time.

On the controller, the stove surface temp fell down to 200 or so and the fire just settled down to a dull orange with some small blue flame but stayed the same physical size as when running. When the timer kicked in, the fire jumped up quickly, less than a minute, and when the thermostat called for heat, the stove came up to normal temps (525-550ish) much much faster. However, I had gotten used to hearing the fan rumble, so when she shut down on pilot mode, the silence kept catching my attention. Also, the stovepipe cooled off to the point where I could keep my hand on it, though when the stoker started up everything seemed to draw just fine.
My overall wondering is I don't want to run that blower all the time if I don't really need to, since what I observed tells me there's not a great advantage. However, is there something I missed or should know about that would change my results? I'm thinking about wear on the grates, having air flowing through all the time like a naturally-aspirated stove as opposed to starving the air and having hot coals cooking them; or the effects of the stack/surface temps rising and falling and so on. Or does this just come down to personal preference, since after 20 minutes or so of good running I can't tell the difference?

Sorry so long, never thought monkeying with the settings for fun could be so much fun

The measurement parameter you want know is the amount of CO in your stoves exhaust. Efficient combustion occurs when you have just the right amount of air, plus a little more for safety reasons. There are instruments that measure the percentage of CO and/or O2 in the flue pipe. Using these numbers and the flue gas temperature you calculate combustion efficiency. Without instruments any operational adjustments are just subjective guesses. Even if you had these instruments many coal stoves, furnaces or boiler have no way to adjust the volume of combustion air. It's just an on-off control. Too much combustion air will reduce appliance efficiency (different from combustion efficiency) by exhausting the heat up your flue pipe. The heat is carried primarily by the nitrogen in the air which just passes through your appliance.

It's all just combustion chemistry. Fuel + Air makes heat. Get the amounts wrong and it's either unsafe or inefficient. The volume of ash says more about the quality of your coal. The ash "look" tells the non-coal impurities in the coal and the clinkers how well you appliance burns that less than ideal coal.

Monkeying with the settings is lots of fun especially if you have instruments. Spouse's think your nuts though.

I've pretty much wondered this same thing. Originally, my Keystoker was set up to run the stoker motor and combustion blower together. When I rewired it, I set it up like the newer stoves and have the combustion motor running all the time. However, I did add the facility to install a SPDT switch to run either in "triburner" mode - with the combustion fan tied to the stoker motor, or in the "modern" mode of 100% combustion fan duty cycle. I never did install the switch, though, I just set it up for "modern" mode.

I discussed this with Keystoker and they said to let the fan run 100% as it will burn better and be more efficient, so I did. Now that I have the stoker apart waiting for my new cam, maybe I'll install that switch and try it out. I may have issues with not having combustion air all the time as my stove idles a lot of the time, and might end up going out, or having a lot of unburnt coal in the ash. Still worth a try, though, I suppose.

Chris

Hi Everyone,

I run my combustion fan all of the time as not doing so the coal is not as burned. it looks similar but the non burned doesnt crush to powder like when its 100%on. The stove is pulling 400 degrees and the air coming from the vent upstairs is about 120 keeping the house at 67 (3 stories) If i cycle the combustion fan the fire goes way down and the stove starts to cool off between that time.

I guess I just wanted to see if one way works better for me, maybe it is just subjective and "personal preference", which is plenty o.k. by me. I'm sure my stove stays warmer when the blower runs all the time, even though it burns the coal bed way back on idle. Then again, it's finally getting cold out, so she won't be idling for hours on end like earlier in the year. Guess I'll keep tinkering, if only for the fun.

The wife claims I'm doing this as an excuse to putter around in a nice warm house more often and work less outside in the cold. But I've caught her gazing into the fire too and watching the flames dance...

Hi Dutchman, try closing the fan inlet flapper down some then run the fan continously. This will stop some of the shrinking of the amount of burning coal, and lower the flue temps some. if the flapper covers say 1/2 the inlet, reduce the opening to 1/3 or 1/4, this will reduce the volume of air through the blower.

Greg L.

But if you close it down too much, you'll push unburnt coal off the end of the grate at high fire rates. It's kinda a balancing act between coal feed and air supply. Ideally, one would adjust the air flow every time a coal feed adjustment is made, so that at max burn rate there is 2" or so of ash at the end of the grate.

LsFarm wrote:Hi Dutchman, try closing the fan inlet flapper down some then run the fan continously. This will stop some of the shrinking of the amount of burning coal, and lower the flue temps some. if the flapper covers say 1/2 the inlet, reduce the opening to 1/3 or 1/4, this will reduce the volume of air through the blower.

Greg L.

Dutchman thanks for the update you are confirming what I have thought and have been finding with mine also, makes no sense to run the fan all the time using electricity and wearing the motor to only turn around and restrict the air flow by 70% or more so you can run the fan all the time . Good theory if I'm selling electricity or fan motors .

The 'theory' behind running the fan continously is to increase the value in my stock in eastern Pa's electric utilities I'm sure the extra $2.00 you spend on electricity will help my stock prices immensely.

Actually, The idea is that if the coal is burned hot by running the fan continously, instead of letting the coal 'smoulder' between run times, then the coal will burn more completely. This adaptation of the 'new style' stokers retrofitted to the old style stokers, has for most people been benificial.. Most burners are seeing significantly less unburnt coal with the full time fan. If you have really good coal, then there may not be any benifit.

I'm sure that if it wasn't benificial at all the 'modern new style' stokers would not be running the fan full time.. BTW, the fans run for years, and extra electicity is minor at best. do the calculations.

I saw a significant reduction in unburnt coal in my ashes in my underfeed stoker when I added a full time fan to keep about 1/2 the regular air volume flowing during 'down time' on the stoker.. I'm talking a 10-15% reduction in burnable coal in the ash.

Greg L

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I am a coal newbie with a Harman Mag and have been experimenting with this since I installed it 2 months ago. Up until last night I could not decide which is better. I am going to run the fan 100% with the restrictor plate 3/4 covered and although I don't like the idea of running the fan 100% it came down to this:

1. The stove seems to run much hotter 325 with stove pipe 110 all the time.
2. The areas of my house that are heated with the coal stove stay warmer.
3. Seems to be less unburnt coal.
4. The blue dancers just look happier and cleaner

Of course I will probably change my mind later this week once I start tinkering again.
I really need to create a journal noting changes made to the stove settings. (Did I just say that. Man I need a hobby )

Just my .02 cents

Mark

Actually a journal is a very good idea, after the burning season, you will not be dealing with the stove daily or weekly, and will soon forget the settings, results etc..[at least I do] so a journal to refer to next fall when the next burning season comes is very helpfull...

Greg L

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Greg, you hit it on the head! I thought about a journal after I started monkeying with my settings- I was allowing several days of burning for each adjustment I made, so it only took me a few days to completely forget what I was doing. I use an extra pocket-size notebook that I get from my seed-corn dealer each spring, and it's on the mantle above the stove, so I can jot down conditions, air and stoker settings, stove & stack temps, coal usage, etc.

What's funny is, I actually enjoy checking and adjusting the stove regularly and making a few notes when I fill the hopper and carry the ashes out every day. All I ever did to the oil furnace was feel cold and " " at the monthly oil bill.