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[Acetylene420]

I've been running the outdoor boiler I built for 6 weeks or so. Knock on wood, everything seems to be going good so far.

I've been fine tuning the boiler operation since I started it up. Slow fan with open flue damper, fast fan with partially closed damper, covered slots in grate, open slots etc...

My question:

Is there any "rule of thumb" for those who run forced draft boilers? Should the fan be on high speed, forcing tons of air into firebox to create a super hot, fast burning fire to heat the water very fast?

Should the fan be slowed down to create a more "stable" fire similar to the rate at which a regular woodstove burns? I'm thinking it would end up using more wood due to the cooler fire.

I currently have the fan turned up quite high and have very little visible smoke coming out of the chimney when the boiler is cycling.

I'm just curious what the rest of you have found to be the most efficient combination of fan speed, damper settings and whatever else you all do.

Thanks everyone!!

[CountryBoyJohn]

I run my damper open 100% and my fan is a single speed, all out!  It really gets roaring!  I talked to a couple guys with the same stove I have and this is what they've found to be most effective, so I haven't tinkered with it.  I get practically no visible smoke and creasote has been a non-issue. 

[fryedaddy]

I try to run mine just beyond smoking.

As soon as I notice the smoke go clear I leave my fan alone. My fan has a plate
I can slide to dampen the fan.

[Wood Nutt]

My stove runs the same as CountryBoyJohn, full open.  If its freshly loaded w/wood, it smokes quite a bit initially, but once the fire gets going good, virtually no visible smoke.  When I load wood, I try to thin my coal bed back toward the center of the stove and try to concentrate the heat toward the middle of the firebox.  Otherwise, it tends to force the air up at the front of the stove by the door and raises the temps at the door considerably.  I think I get better heat transfer from the firebox to the water if I keep the heat concentrattion nearer to the center of the firebox.  No scientific evidence of this, but makes me feel better!

[SKAMPO]

On mine if I have the damper wide open it will shoot flames out the stack. Not very efficient if you ask me, sure theirs no smoke but it's forcing a lot of heat out the stack. I like the recommendation of running the fan just on the verge of smoking, that's what I shoot for on mine also. 

[MattyNH]

 Just one speed option on my fan..It turns on, then when the thermostat is satisfied fan will turn off..My boiler smokes the most after a fill up..After the first cycle or 2.. After that theres nothing for smoke..

[Flyfishjt]

Just curious as to where and what your dampers look like. I've been having an issue with smoke on my earth and I'm beginning to wonder if it's more of a air volume issue. Idk

[yoderheating]

 If you have an efficient furnace that captures the heat ( like country boy has) then run the fan wide open. It will burn cleaner and keep the furnace cleaner. If you have an inefficient furnace and you get flame out the stack I would turn it down some just for safety concerns.   

[RSI]

On mine if I have the damper wide open it will shoot flames out the stack. Not very efficient if you ask me, sure theirs no smoke but it's forcing a lot of heat out the stack. I like the recommendation of running the fan just on the verge of smoking, that's what I shoot for on mine also. 

You have a damper on a nature's comfort NCB175? If it is shooting flames out when you open it, it is probably burning out the creosote that built up in the chimney because of the damper. Try leaving it open and cutting back the intake air. That is how it was designed to operate.

[Acetylene420]

First, thanks to everyone for all of the info!

I can see the consensus is open damper with high fan speed. That's what I was thinking also.

I assume the idea is to get the wood burning super hot and super fast with minimal cycle times.

I'm going to try a higher fan speed along with openings damper much more than it is.

Ill let you know what happens.

Thanks again everyone!