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[skorpyd]

I fired up my homebuilt OWB on Tuesday.  Today I noticed that when the forced air draft fan was on it was sounding like it was chugging and some smoke was coming back out of the fan unit itself.

I used a commercial door unit with the solenoid operated fan installed in the door.  I believe it's about a 65 cfm rating.  I have a 6" flue.

I don't recall much of this last year, my first year or actually half year.

I did extend the flue a bit lower in the fire box and also added about 4' to the flue pipe as I added a shed around the unit.

I'm wondering if I need a higher cfm blower or if there are any other ideas.

Thanks

[swede]

Perhaps some flue obstruction?

[skorpyd]

I was wondering about that, but when I cleaned out the horizontal portion of my flue it wasn't that clogged, and the diameter of the fan outlet is much smaller than the flue system.

[RSI]

Is your wood super dry or did you have the door open and let it get burning real hot before this happened?

The chugging is it burning up the air and smothering the fire and re-igniting as soon as there is enough oxygen again.

[yotehunter66]

Can you video it when it's happening? Might make it easier for us to understand what's happening.

[slimjim]

I think what you are experiencing is to much fire and not enough air flow, try reducing the amount of wood you put in at one time to reduce the charcoal bed, it gets so hot that the wood flashes, creating lots of smoke and then the blower can't push enough air in to get complete combustion, when it does combust it creates a mini explosion and the cycle repeats itself. Try lowering the amount of fuel loaded at one time and I think you will find that the chugging will subside!

[yotehunter66]

Too small a flue size for the volume of the fire box or too small of a fan? Could be both. What say you Slim?

[slimjim]

Certainly could be but I'd bet on to much fuel and the fuel is flashing, try lighter loads, more often especially when there is not much load on the system.

[mlappin]

Under lower heat loads could you just unhook the fan and see if it will draw naturally?

[slimjim]

I suppose you could! perhaps that would help to keep the fire small!

[mlappin]

I suppose you could! perhaps that would help to keep the fire small!

If I was to keep the first one I built around much longer I have tossed the ideal around of getting a two stage controller and having step one be natural draft and if the temp dropped too far have stage two be a forced draft.

[skorpyd]

Thanks all for the responses,

I had just loaded the firebox for an overnight burn and possibly some obstruction near the flue opening and a fairly fully loaded firebox.

I guess I am wondering about the lighter loads idea being a problem when the temps are down and I'm wanting to at least get a 10-12 hour burn.