Continuous draft fan running or only when stoker motor runs?

I'm in the process of 'restoring' an older model Keystoker 90 direct vent stove. Upon disassembly, I noticed that the draft blower motor and stoker gear motor were wired together, so that they only run when calling for coal feed.

In the manual I have, the wiring diagram shows them separate, and the draft motor runs 100% (along with the direct vent motor, of course). That's how all the new stoves are designed.

I want to know why it improves the stove operation to have the draft blower running all the time? IMHO, I would think that if the stove is just idling, the natural draft should be enough to keep the fire running at a low level, and since there is no fuel being fed, why blast what's there with a bunch of draft? I would think the extra air being fed for a low firing rate would just blow heat up the stack.

Conversely, if the stove is running at 100% firing rate with a full grate of coal and the thermostat shuts off the feed and draft blower, is it going to push a bunch of unburnt coal off the end of the grate?

I think that in reality, the combustion blower and coal feed should be tied together, not unlike a carburetor. More fuel feed requires more air, etc. Ramp the blower speed to match the coal feed rate.

Maybe I'm going to have to build up a PLC control system.......

chris

I would contact Keystoker, seems like a great bunch there. They know the stove and why the changes were made. I'm sure a call to them would net you what you need to know, and how best to update your unit. There may be other changes to the stove and or equipment required.
Most manufacturers will be more than happy to deal with customers questions and try to be helpful, it's just good business.

Hi Chris,

Coaledsweat is correct, the Keystoker peole are very helpful.

One other thing to remember that when your stove is operating on the timer during idle state (Tstat not calling for heat), there will be coal burning with no new coal being fed. For this reason the combustion blower should still operate to keep the fire going.

I encountered this problem on my Alaska stoves with the triburner stoker units. Once the feed rate got low enough the fire would not be hot enough to prevent unburned peices of coal since the blower is driven by the stoker motor. For that reason I added a seperate combustion fan to boost the process and prevent unburned coal during the idle/low fire part of the process.

Have fun with the science project!

Our keystoker 90 Combustion blower and Direct Vent run 100% of the time. But the stoker is hooked to the thermostat and timer box.

Even without the direct vent now that I have it connected to the chimney, even when the power goes out, I have about 20-30 mins until it completely flames out. There is a draft, but it can't draw enough under the coals to keep the fire going. I have warm coals, but not enough to restart. Maybe with Buckwheat, it may continue to burn a little better without combustion air, since there is more airflow around the coal.

I have mixed the Buckwheat and Rice when it was really cold to avoid the clinkers being formed.

I don't think you have enough draft on a direct vent, if you turn it off.

Does yours have the Internmatic Timer Box? That will feed a little when the thermostat is satisfied and keep a very small fire burning, without running unburnt coal off the end. Ours is set to 1.5 Mins ON/ 10 Minutes off. About 1 Stroke every 10 Mins.

WNY wrote:Our keystoker 90 Combustion blower and Direct Vent run 100% of the time. But the stoker is hooked to the thermostat and timer box.

I don't think you have enough draft on a direct vent, if you turn it off.

Does yours have the Internmatic Timer Box? That will feed a little when the thermostat is satisfied and keep a very small fire burning, without running unburnt coal off the end. Ours is set to 1.5 Mins ON/ 10 Minutes off. About 1 Stroke every 10 Mins.

Yup, I have the same timer box. Currently, the stove is wired so the combustion fan and stoker run at the same time (or don't run). The direct vent fan will run 100%. With a direct vent, if the power goes out, the stove is going to go out very very fast.

I was just curious as to the reasoning behind running the combustion fan constantly vs. with the stoker motor.

The easy answer would be to run it both ways and see what happens!

Chris

Chris wrote:

"I was just curious as to the reasoning behind running the combustion fan constantly vs. with the stoker motor. "

The way I think about it is that when the fresh coal is pushed onto the grate, it takes 10-30 minutes to burn it fully. Without the combustion air blower running, it will not burn the fresh coal completely.

Leisure Line found on their stoker units that had an off/on/variable reostat, that the customers were turning down the reostat, making the combustion fan run slower along with the pusher motor. The result was fires were going out and more unburnt coal.

The newer LL units prior to the CoalTrol have only an on/off switch for the stoker unit. The heat is controled by adjusting the pusher block stroke.

With the CoalTrol, the pusher block is designed to push maximum, there is no adjustment, and the coal trol does all the adjusting for you.

So I'd run the combustion fan continously, you will get more complete burn of your coal.

Greg L

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My stoker fan and fuel feed are mechanically tied together via reduction gearing.

It strikes me that it would be a lot more complicated to separate them, although when it gets warm (like last night when the low was about 50°) and the thermostat isn't calling for heat, it does get tricky to keep a "cool" fire going. I throttle down the fuel feed and use a timer that cycles the blower/stoker to run about 45 sec 4 times in the 1/2-hr timer cycle, i.e., once each 7.5 min. But I had to manually advance the timer several times to keep it going last night. At present, my timer is running the blower 10% of the time in the aggregate; I'd like to try increasing that by lengthening the blower time to 1 min and maybe increasing the frequency to 5x/cycle, or once each 6 minutes. That would increase my minimum stoke time to 16.66% from 10%.

The fundamental problem is that, when there's little call for heat, naturally the ambient temp is higher so there's minimal natural draft. Because we're expecting another bout of cold this weekend, I wanted to keep the fire going so I don't have to f*** around lighting it again.

Operationally, I think this borderline heating range is the biggest challenge to those of us coal-burners who seek maximum automation -- the girlie men. And logic tells me that there are two ways to deal with it: (1) finding the finer points of keepin' them fires burnin', or (2) automating the reignition process with some sort of dual fuel rig.

I've saved "a ton" of $ heating with anthracite this season. I just want to get it even more user-friendly.

Stockingfull, can you rig up a small blower fan, to blow into the fan housing inlet?? This way you will get some additional combustion air to the coal bed, keeping it going a bit better than just the reduced draft can.

Take a look at this fan:
http://www.englandsstoveworks.com/manua ... ctions.pdf


Or just try an old hair blow-dryer for one day or night, it will not stand up to continous use for very long, so don't take your wife's off the dresser!!

I think any positive pressure through the coal bed will also help the chimney draft better too.

Greg L

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A cheap timer to give it a 1 minute huff every 10?

The problem is, when you uncouple the air from the fuel, you run the opposite risk: burning out your fuel.

And if you put enough fuel in to match the continuous- or increased air, you might as well just turn up your thermostat, because you'll be getting a bunch more heat.

Actually, that's what I did yesterday to save the fire about 6PM, I saw it was about to die as we were about to step out for dinner, so I just pushed up the thermostat and let the thing heat the whole house up 5 degrees.

But that just postponed the problem until later, when I wanted to let it cool down for the night....

Just had an idea: for an HVAC system, why not just install a switch to disconnect the plenum blower in mild weather?

The way mine's hooked up, I can only choose between "on" and "auto" for the plenum blower. But, if I want to keep the fire going w/o heating the house, certainly defeating the circulation fan will help -- there'll still be some "gravity flow" of heat up through the ductwork but it'll surely be far less than forced air.

Simple, inexpensive solution that would give a little more leeway to run a "hotter" fire.