Please help, getting smoke back when placing 55gl drum

I just started my first RMH. I set up everything out side to make sure it worked before bringing it in. I can give more info on how I built it if someone needs to know specifics, but basically I lit it up without the 55 gl drum in place and everything was working great! No smoke back, sounded rockety. Then I placed the drum over the vent tube and I began to get smoke back and finally the fire went out. The vent tube was 1 3/4 shorter than the top of the drum. Anyone have any idea why placing the drum would cut off the draw? Thanks

do you have a photo of it? I'm not a RMH pro but that would help anyone that is .

Craig thanks for the reply. I don't have a picture yet. I did some research and I believe that the space between my riser and the barrel is to large. I'm using a 6 in pipe. Turns out the proper distance should be 1.5 in. After a remeasure I have 2 in. Going to shorten that area and see if there is a difference.

Ok I tried shortening the distance and I'm still getting smoke back. Here are some pics.

Hi Rick,
As Craig said above, without pictures or details of your system any guess work is just that, a shot in the dark; nor am I a great expert on RMHs...

However, most problems at this point in the construction come from either inadaquite insulation of the heat riser and/or insufficient size of the manifold (where the flue gas exits at the bottom of the barrel).

Can you describe your system in those areas? Maybe the gurus on the forums can help.

*Edit You posted pictures while I was writing. Yay! You definatly need to insulate your heat riser. No manifold as of yet. Make it bigger than you'd think when you do make one What material is your combustion chamber made of? If it's not a insulative material your burn (and therefor draw) will also suffer. Looks like marble?

Chirs, the manifold is a little over 6 in sq. I was going to insulate the riser when I brought it in the house. Does the uninsulated riser really make a difference in smoke back?

Yeah, it does. The physics are like this: the heat inside the riser causes the less dense flue gasses to get pushed up into the barrel. The radient heat loss of the barrel's metal causes the flue gass to become more dence (colder) and fall down the sides of the barrel to the manifold, it vacating that space to decend creates even more draw up through the heat riser... and so forth... it's a limited possitive feedback system.
However, if the heat riser is not insulated, it's metal radiates heat into the barrel's space and heats all the air in there to a more or less even temperature. Therefor even gas densities, therefor no draw.
I hope I explained that well, it's not bang-on accurate, but it's a good mental image to help picture what's going on.

yes. the entire combustion area - feed, tube and riser - must be insulated for this to work. It will rocket without a bell (drum) every time. putting the bell on is when it all changes. First, the combustion area must get really hot. Like 1000 degrees. My original steel core glows red when I run it. Second, there _must_ be a heat differential between the riser temp and the bell temp. That means insulation. After the riser gases hit the bell top, radiate heat off, you need something to maintain that temp difference. The temp diff is part of what drives the draw through the rest of the system. What you have now is a really hot steel riser....and then you put on a barrel. The temp will try and or will succeed in equalizing. So not really doing anything to drive it.

on edit: look at the videos online again if you havent already. You will see every one of them had a riser, surrounded by insulation (frequently vermiculite mixed with clay) contained by another shell of sheet metal.

Here's an earlier thread about a similar issue. Hopefully Ernie's answers can help you too.
https://permies.com/t/12031/stoves/losing-draft-put-lid

Thanks for finding that for me Chris! I'll keep working at it.

'The Permies Cloud' : If Apple can have an iCloud, we certainly can have a Permies cloud, or Pcloud, (and you thought you could only see them on really bitter cold days !)

Anyhow, can Rick Stevenson or any other surviving members of this thread tell me the proper brand name or any brand name for this kind of stove pipe ! BIG AL

allen lumley wrote:
Anyhow, can Rick Stevenson or any other surviving members of this thread tell me the proper brand name or any brand name for this kind of stove pipe ! BIG AL

Allen,

do you mean the duct he is using? Not sure it has a brand name, it's just a regular round air duct that is available in some places. I am buying a similar one here in Japan. They might be in metric countries only, not sure.
Mine is 150 mm (6") by 4 meters long (about 4 yards?)
it costs me about $25 for that piece.

Allen, that no stove pipe, that's HVAC pipe.

Allen, I discovered that HVAC pipe is not very good for the stack. The temperature inside the stack gets 700 - 1000 degrees and that type of pipe disintegrates under those temperatures. The better solution is to use firebrick that is rated for those temperatures. This can be purchased at stone and masonry dealers. Fire bricks are 9 X 4 inches and are either 3 or 2 1/2 thick. I was able to purchase the bricks for $1.90 if memory serves. Good luck.

et al : My bad, I was so focused on what I wanted to do with the piping > use it for a horizontal chimney that when I asked for a brand name or two I called it smoke pipe
Stove pipe, yes I know it is hevac, living in a township with no stop signs there is not much commercial development, and I am rather glad till I need a fitting ! Thanks
everyone any way ! for the craft BIG AL !

I know this thread is a bit aged but just to answer Allen's question and provide info for future viewers, the duct is called spiral duct and it is indeed used in HVAC.
Jim

allen lumley wrote:et al : My bad, I was so focused on what I wanted to do with the piping > use it for a horizontal chimney that when I asked for a brand name or two I called it smoke pipe
Stove pipe, yes I know it is hevac, living in a township with no stop signs there is not much commercial development, and I am rather glad till I need a fitting ! Thanks
everyone any way ! for the craft BIG AL !