OK AIM, air under or over... let's hear it.

[Whitespider]

But I'm headin' in the bedroom to read a little before turnin' in... might be mornin' before I read your post.

 

[Chris-PA]

Some like it on top.

 

[NSMaple1]

My vote is THROUGH.

 

[AIM]

While introducing air under the fire might make the most LOGICAL sense I have found that in SOME circumstances just doesn't seem to work all that well. (For the record I am not just talking about MY boiler,, I have seen this a few times)
AIR,,,, Like water and electricity will find the path of least resistance.. Frequently the air will burn a HOLE through your fire and the wood around that HOLE will not get the DIRECT air wanted to burn HOT... Now you might think that the air will still circulate through the firebox and have the same effect but in my experience this just doesn't seem to happen. The air SEEMS to simply burn the hole and go up the stack while allowing the wood surrounding the hole to not burn HOT...
IF I ever build the new boiler I have drawn up the air will blow across the fire and not under. Air from below is not the answer to all problems. It simply doesn't work like logic says it should.

 

[AIM]

I am talking forced air not natural draft.

 

[AIM]

I have ZERO experience with natural draft.

 

[woodchuck357]

After making changes to a stove that came with an over door main draft and a top secondary, by adding a grate in the floor and an ash box with a screw type draft in its door, that is the only type I would consider buying or building. I like the advantages of secondary burn and I like watching the fire thru the glass but need the versatility of having air flow up when starting a fire and getting the most heat from the coals, as well as ease of ash removal the grate and ash pan provide.

 

[Jake Wise]

I am thinking about adding a grate to the boiler I built. Right now the air comes out holes at the bottom of the door which ends up being below the level of the fire due to ash build up (I keep the first six inches of box clear of ashes so the holes aren't blocked). This leads to the wood at the front burning down faster than at the back so before each load I have to take my fire rake and level it out. I don't know if this is similar to what AIM is talking about when he said across or not. My set up is usable but I think it could be better.

 

[AIM]

I am thinking about adding a grate to the boiler I built. Right now the air comes out holes at the bottom of the door which ends up being below the level of the fire due to ash build up (I keep the first six inches of box clear of ashes so the holes aren't blocked). This leads to the wood at the front burning down faster than at the back so before each load I have to take my fire rake and level it out. I don't know if this is similar to what AIM is talking about when he said across or not. My set up is usable but I think it could be better.

Sort of but more of a top down air. My new design has my inducer fan mounted in the upper part of the door blowing down at an angle across the fire.
The boiler I have now i built with the air getting blown under the fire (like I said logic says it should be better) but frequently I just get a hole burned in my fire.
Oh don't get me wrong it works pretty decent regardless but it does have it's flaws.
I will though throw out the possibility that I am simply blowing to much air to hard. I have thought about finding a much slower fan. The fan I use now is a furnace draft fan which blows quite a lot of air at a pretty high velocity. Maybe a slower fan might not burn the hole???

 

[Whitespider]

I've had the "hole" burn through the fire with both natural and forced draft, it's sort'a like when the fire bridges... it ain't a perfect world I reckon. Bridging will eventually correct itself as the fire collapses, but that ain't always true with the "hole". I'm not sure if a strong, high velocity, forced draft would increase the odds of it happening... but it makes sense it would.

If the grate gets plugged with small "clinkers" (most often form burning elm) the "hole" burn-through will happen at points where the grate vents are open. Also, burning oak, I sometimes have it happen when running a deep coal bed during extreme cold weather... but a quick raking of the coals normally opens the vents again. I made my coal "rake" with tines slightly smaller than the vent slots; if grate plugging gets bad enough I can use either of the end tines (by tipping the rake at a angle) to clear them. But 99% of the time, provided there ain't too much ash on the plugged grate, a good hot fire will open things back up.

It's been cold here and we've been running a deep coal bed. When I got home last night I could tell the grate vents were plugged by the amount of ash mixed with the coals on the grate... and there was two "holes" burned through the coal bed. I raked it and opened the ash drawer to flood the coal bed with oxygen while I took my boots off, grabbed a beer, and whatnot. Wasn't but 3-4 minutes and I heard the tink noises as the grate heated up and the lodged "klinkers" started falling free into the ash drawer. By the time I finished my beer the grate was clear, and I raked a full drawer of ash off it before loading.
No "hole" in the coal bed this morning.
*

 

[Jake Wise]

Maybe a slower fan might not burn the hole???

I ended up having to add a rheostat and then also cover half the blower intake with duct tape. It seems like the ideal solution would be to have the air come from above and/or below depending on your needs.

If the grate gets plugged with small "clinkers" (most often form burning elm)

The stove we had in the shop growing up had a grate in it that pivoted in the middle a slight amount so you could put a special wrench on a lug and jiggle it until all the ash fell into the drawer. That would be ideal but much harder to engineer.

 

[Whitespider]

The stove we had in the shop growing up had a grate in it that pivoted in the middle a slight amount so you could put a special wrench on a lug and jiggle it until all the ash fell into the drawer. That would be ideal but much harder to engineer.

A coal shaker grate?? They work real well.
*

 

[Jake Wise]

@AIM are you still using the wood burner that you posted pics of in your first post on here? I also have a owb made out of a 250 and a 500 gallon tank, but mine are laying flat. It looks like you have been running yours for a few years now and I wondered if you had made any tweaks to it, mine doesn't seem to be as efficient as I feel it could be and since our designs are similar I thought you might have some insights. I think my main problem right now is heat exiting the fire box too fast. Do you have any kind of baffle in your stove to deal with that issue?