Throttling Down a Fire

Lightning wrote:Ok partner.. it's all about maintaining draft. I'm gonna ask you to think outside the box here for a minute. Open the Mpd completely. Then open your secondary air and cut the primary to a sliver. The extra air coming in over the fire will keep your draft moving but won't contribute to more combustion. The sliver of primary air will keep her alive, but asleep..

On my Glenwood this doesn't work at all. Opening my secondary (top door) air makes my fire burn hotter. In fact, the Glenwood likes secondary air a lot and I use the secondary air to heat things up all the time. I have not found that it lowers the BTU output of the stove - rather the opposite. On your stove that may differ...

If I leave my MPD open, I burn a lot of coal fast - how fast depends upon how I have my air intakes set, but always significantly faster than closing it down.

The only way I've ever gotten my Glenwood to run really low (like 150F or less) is closing all the dampers and the MPD. Also have to play with the right amount of ash build up.

I'd say the best option for Simon is to try the smaller firepot, for all the work that may entail, I think that may be the best possible answer if he's interested in running down that low...

dj

How about some pea coal? I always read everyone saying try a smaller pot, well in my hand fed furnace, which holds about 70-80 pounds I am able to run it at 130-150 for a month with no problems with 24hr tends, and that my friend is no small fire pot.

hotblast1357 wrote:How about some pea coal? I always read everyone saying try a smaller pot, well in my hand fed furnace, which holds about 70-80 pounds I am able to run it at 130-150 for a month with no problems with 24hr tends, and that my friend is no small fire pot.

I can barely get any heat of pea but feed it nut and I can move the temp up or down 300 degrees in a matter of minutes. I read how slow coal is to respond but that's not what I'm experiencing.

dlj wrote:On my Glenwood this doesn't work at all. Opening my secondary (top door) air makes my fire burn hotter. In fact, the Glenwood likes secondary air a lot and I use the secondary air to heat things up all the time. I have not found that it lowers the BTU output of the stove - rather the opposite. On your stove that may differ...

If I leave my MPD open, I burn a lot of coal fast - how fast depends upon how I have my air intakes set, but always significantly faster than closing it down.

The only way I've ever gotten my Glenwood to run really low (like 150F or less) is closing all the dampers and the MPD. Also have to play with the right amount of ash build up.

Just to be clear we are talking about air coming in over the fuel bed, right?
Do you have a manometer installed? All of these details point in the same direction, your stove isn't tight. The secondary air is making your draft stronger which makes it draw in more air from an unknown source underneath the grates. If you can open the secondary air and close the primary down to a sliver and the stove goes hotter then you may be leaking air into the stove around the ash pan door seal or somewhere else that you are unaware of..

Even with the MPD open you should be able to starve the fire with the primary air control, unless air can get in under the grates somehow, somewhere else.

Lee,

I tried your method with my range yesterday - taking and writing down heat readings at various places, plus stack temp and mano readings every half hour.

As you may know the range works like a base heater, but with a smaller firebox.

I closed the slide primary to a sliver - .040 just on the two end slots. Then I opened the secondarys half way (anymore then that has killed the fire in past) and the MPD fully. Mano stayed at .02. Like Dave found out with his #6, the cook top and stack temps went up and stayed up for quite a while.

Then I tried just closing the MPD all the way. That got the mano down to .01 and slowly over the course of three hours the stove top temps started to drop. After that the temps leveled off, they were still higher then what I would call warm-weather cruising temps. The cook top averaging just over 500 over the firebox and the stack staying in the low 130's.

If I were to close all the dampers and just let it run on the small amounts of air leakage built into it, such as the ash door and primary slide damper edges, then just use the check damper to control it, I can get that stack temp down into the 90's, which kills the draft enough to lower the stove top to around 400 average and it will idle along like that all day. What would likely equate to about 200 on a barrel stove ?

These old stoves were called "air tight" in their day, but they are not air tight by today's standards of gasketed doors. So yes, there is some constant air leakage below the grates with these old stoves. But, that is not always because of leaks caused by loose, or missing caulking, or broken parts. It is factored into the design. And so is a way to lower the draft strength to compensate for that built-in below grates air leakage, without increasing the temp by burning more of the top layer of coal as the secondaries do. It's the check dampers near the stack base (or internal by-pass check dampers), which are too far down stream to add to the burn.

Paul

Try a 50/50 nut pea mix, this is what I'm burning in the coral Andes

Hey Paul, nicely written! You guys with your antique stoves that don't use manometers (some) or barometric dampers have to fly by instinct which is very commendable..

I guess you could say I'm spoiled with my gadgets and controllability of using an airtight appliance. I forget that isn't always the case so tricks that work for me, might not work for someone else..

When you see the pipe temp rise when adding secondary air, mine does too. My thinking is that the temp rise on pipe isn't because the fire is burning hotter, it's because more air mass is passing thru the pipe and can transfer more heat to the pipe. Like a wind chill in reverse. I realize that might sound a little crazy but it's the only way I can explain that the pipe gets warmer and my furnace gets cooler lol.

Another 2 cents.....

On my setup the only time opening the secondaries adds heat is when the initial volatiles are burning. After they have burned off, leaving the secondary air open will result in cooler stack and barrel temps. Closing them then increases stove temps.

Lightning, its ok cuz I have my manometer hooked to mine and already have the T for the baro install, I just have to get the baro, I know now that once it gets cold and the winds come back in gonna need both for a nice steady cruze. Even though there "forbidden" on base burners lol

I start by letting the ash build up. Poke from the top to knock the ash down but don't shake. Then load it up real good, the more I get in the longer the idle fire will last. The bed of semi-compressed ash cuts back the under-fire air.
Let it catch, an hour or so is usually plenty.
Then close all the intake dampers and open the check damper. There is still enough air that leaks in to keep the fire going and keeps the exhaust gasses going up the chimney.
Then cut the MPD to 1/8-1/4 open. If it's real windy a little more (my chimney doesn't like very windy days)

It will go days like this. After about 2 days there is usually room for a little more coal and I top it off, gets another day or 2. Temps are around 80 at the pipe through the wall and in the 100's on the stove barrel.

To wake it up, return everything to normal, shake and let warm up. Once it's warmed up, load fresh coal slowly.

I've never lost a fire while idling. I don't know how long I can go like this but I've made it around 4 days no problems at all. My only limit would be on space for ash, could probably shake a little and go forever.

scalabro wrote:Another 2 cents.....

On my setup the only time opening the secondaries adds heat is when the initial volatiles are burning. After they have burned off, leaving the secondary air open will result in cooler stack and barrel temps. Closing them then increases stove temps.

Try opening the secondary air back up during a mature fire (at about 6-7 hours into the burn) to see if stack temp inflates a few degrees. I can see it on a digital thermometer. A magnetic temp gauge might be harder to tell.

Coalnewbie, I apologize if I contributed to any derailment of your thread..

Lee,

Since we're all burning coal, it's understandably easy to think that these stoves are more alike. However, on looking closer, I find it fascinating that small differences in design can have such a big affect on how the stoves preform.

This thread is a prime example.

Paul

Lightning wrote:

scalabro wrote:Another 2 cents.....

On my setup the only time opening the secondaries adds heat is when the initial volatiles are burning. After they have burned off, leaving the secondary air open will result in cooler stack and barrel temps. Closing them then increases stove temps.

Try opening the secondary air back up during a mature fire (at about 6-7 hours into the burn) to see if stack temp inflates a few degrees. I can see it on a digital thermometer. A magnetic temp gauge might be harder to tell.

Tried that with calibrated instruments and have been down that road. It cools off after the majority of volatiles are burned off with the secondary open.

Lightning wrote: Just to be clear we are talking about air coming in over the fuel bed, right?
Do you have a manometer installed? All of these details point in the same direction, your stove isn't tight. The secondary air is making your draft stronger which makes it draw in more air from an unknown source underneath the grates. If you can open the secondary air and close the primary down to a sliver and the stove goes hotter then you may be leaking air into the stove around the ash pan door seal or somewhere else that you are unaware of..

Even with the MPD open you should be able to starve the fire with the primary air control, unless air can get in under the grates somehow, somewhere else.

Lightning.

Yes, talking about over the fuel bed. No manometer, although I'd accept anyone wishing to donate one to me - I won't purchase one, as it does nothing to enhance my bottom line... I do have excellent draft on my chimney, something I feel that these baseburners perform better having....

You might be right, but I am quite skeptical. Having run my stove for decades, I've also had it in various states of "repair", from quite "loose" to quite "tight". And I have certainly had my stove such that the bottom end is very tight. Now, the top end, not the case. That has always been pretty loose. The top door of my two front doors has never closed really tightly. But we are talking bottom air...

I ask what type coal do you burn? I always burn stove coal. I feel that with stove coal there is enough room around the coal pieces that air from the top side can participate in the combustion. If I'm running my stove with little to no bottom fed air and am running just with the secondary air feed, then my coal burns from the front of my stove towards the back, as one would imagine from where the air is coming from. If I were using nut or smaller, that could well be not the case. Don't know.

When my stove is quite "tight", I can starve the fire by closing off all the air vents (not the case right now as I've got a leak somewhere that is totally irritating me...spring time will see me tearing this stove apart and re-sealing everything...). BUT - if I don't close bottom AND top vents, the fire will go on.... Yes, I can lower the BTU output of the stove into the room by opening my MPD as more goes up the chimney, but that is only compared to running the stove "correctly" with the MPD closed down.

As far as a baro - I don't feel they are appropriate for base burners. They need strong draft from time to time. Baros are much more appropriate on other coal appliances...

I've sometimes wished I could pump compressed air into my stove - but that I'll leave for another discussion...

dj

What works in my No. 6: close primaries completely, open secondary over-coal air. Close exhaust damper. Let ash build up a bit. If fire threatens to extinguish, open damper as necessary.