Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: skorpyd on January 25, 2014, 11:10:25 AM
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My home built OWB (can be seen on Home Made section) has been online for a week now. It has been very cold here and I'm very thankful to not be using propane. I have been using lots of wood though, and it seems to not be burning the wood completely. I have filled it up almost to the door with small chunks of basically charcoal.
(http://farm3.staticflickr.com/2893/12136783773_ea7c7e3342_z.jpg)
One day this week I got home from work and the wood I had put in before work was gone, and the bed of coals left was not burning. The temps were way down. 100 degree coming back to unit and about 120 coming out.
The blower fan was on but the coals were not lit up.
I purchased a commercially made door from Burnrite with the integrated blower so I figured this would be a good set up. One thing I did yesterday was to install a diverter on the lower blower exits, thinking that shooting the air more downward into the fire would help.
(http://farm4.staticflickr.com/3725/12136522255_086d0fc8fa_z.jpg)
It was inconclusive as I put wood in this morning at 4:00am and at 11:00am most of the wood was gone and the temps were starting to come down at the boiler.
I then left the door open slightly where the fan was blowing onto the coals and getting more air into the unit with the open door. The coals started to light up and the temps also started coming up .
So I guess that is telling me it's not getting enough air. I'm just wondering what some of you veteran users have to say about it. I was expecting to burn the coals down to a fine ash but so far thats not happening.
The blower only has about a 2" diameter exit coming out of it so maybe I need a bigger one. I also have a 6" flue pipe. Blower model is a Fasco model 50748-D500.
(http://farm4.staticflickr.com/3795/12136797193_e10798f1fc_z.jpg)
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How far below the opening is the bottom of the firebox?
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I would say 10-12 inches. Basically what the square frame of the door versus the round opening of the firebox made reasonable.
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I have a burnrite 228 and it has a 8 inch chimney. Is your chimney plugged? What temps you running? I wonder if you should cut away some more of your chimney pipe that comes down into the firebox. Those are 100cfm fans and mine does fine for draft but i have a baffle design so maybe thats the draft difference.
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It looks like you need less wood and more air. I just checked, my blower is rated at 146 cfm, not sure how that compares to your blower.
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It just looks like you need more air space for heat to get up and out that chimney.
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any way to get the blown air under the wood?
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You need to shoot that air into the coal bed. It looks like it shoots it straight 45 degrees up into the firebox. You need to fan those coals hard with the blower. I don't know how burnrite builds there opening compared with their door but I would guess that it is much different then yours. I would weld on another piece of 2x2 box or whatever that nozzle is and shoot the air down into the coal bed. You should burn everything up then.
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It looks like Burnrite has the exhaust exit the front of the firebox. With your setup you are blowing the air straight to the chimney.
Is there any chance you can move the blower to the ash door? If not, I think you will need to try keeping a larger pile of wood in the center of the firebox. You need to air to pass through the fire before it gets to the chimney.
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As others have stated, you got to get that air at the bottom of the coals - You seem to be blowing it right over top of them.
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Thanks for the thoughts guys,
Just to clarify, the model of fan that I have is only 65 cfm with a slightly more than 2" exit diameter from the blower.
The air supply/exhaust into fire box has 3 openings, the square one in the pic that blows right towards the flue opening and basically over the fire and then there are 2 on the bottom that are about 3/4"x3" pointing straight out from the bottom of the door frame.
I added the bent piece of steel to try to deflect air from those bottom ports more towards the bottom of firebox/ashes.
I have found a 130 cfm Dayton blower that will fit into the existing box with it looks like only small modification. So I'm thinking of trying that.
Maybe covering that top exhaust port to direct all or most of the air more downward would help also. I'm wondering though if I would be constricting my blower too much. Right now though it does not feel like there is a very high velocity of air coming out when the fan is on.
If the flue is not large enough then that would be major and I would just have to live with making charcoal.
I have thought about facing the opening in the flue towards the back. That would in effect be making the smoke go through 3 90 degree turns to get out. I don't know if that would make things better or worse though.
Using the ash door for combustion air is doable. It just means redoing the whole air supply system, so I am hoping to find an easier fix first. It would have to be an off season project.
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OHHH I see the lower ports for air now. If it were me the first thing I would do is try occluding that top square piece that just shoots air over the fire forcing all of your air to shoot into the coal bed. After that I would go with a bigger fan if that doesn't help. Plenty of units with in door fans so it should work ok for you with some tweaks. Just need to get that air into the coal bed instead of up high. Your flue size is fine, it is much more important when you have a natural draft stove to have the flue size correct. Shaver uses a 5 inch flue and they are very similar to yours.
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to me,on the pic the angle of the air going into the firebox looks like it would be blowing to the top of the firebox.
if it was mine i`d take the door off and just weld either a small flat plate or maybe a piece of channel say 2`` long just to help divert the air down to the fire. to me you air intake is o.k just your angle to the fire is off.like someone else said ,your blowing right over the coal.
good luck
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I just covered the square opening on top to divert air to lower openings. We'll see how it goes.
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Let us know. I think it will help a lot. Your fan is pretty small so you may need an upgrade but worth a shot first.
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I think the guys are on the right track about directing your airflow, another thing that can lead to a lot of charcoal, how big a pieces of wood are you burning? I'll get the same if the wife adds wood to ours, nothing but small pieces leads to a lot of charcoal. About time that happens I'll put in big enough pieces that three or four will fill the fire box, end of charcoal.
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If the previous suggestions don't help how about putting a partial "grate" in, something that starts near the back wall of the firebox to about half or 2/3 way to the door. that way you could still rake the ashes from underneath it, and if you did that every loading or two, it might leave a place where air could get under the coals also.
Hope you get it figured out, I copied your design in many ways and would expect mine to behave similarly.
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My opinion is that the fan is too small. I have a pacific western and with the big blower I can blow the coals until they are all gone. When I first set it up I was getting huge amounts of coals, turns out I was putting too much wood in it and too often. I didn't have enough of a heat draw from it either. If your temps are going down and there is still coals then it means the air is not blasting the ashes off the coal and burning them up to get the heat from them. 1st I would cover that small square vent using steel and a couple of screws. If that doesn't work then upgrade to a bigger fan. Your door looks pretty much the same as mine and mine works good now that I understand it. I still get lots of coals but it's because of my work and fill times. As long as it's heating the 2 houses the coals don't bother me.
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I'm sure part of the problem is learning how my boiler likes to burn and how to vary that with outside temps.
I am not sure yet how well the coals burned or will burn from last night, but it was a pretty good night. I filled it a 8pm with a mix of small and larger rounds (dry ash), I got up at 5am and the house was warm(a good sign). I went out to boiler and the fan was not running, (another good sign). From what I could tell as I couldn't see much with all the smoke in my headlamp I still had a couple pieces of wood and a fair amount of coals. I will have to load it up again before work.
This was much better burning than previous. Must be due to the fact that I got the front insulated and sided yesterday along with covering that square blower vent to divert the air downward. It was very cold and windy last night.
I'm still leaning towards a larger fan though.