Exhaust to Burn Tunnel height ratio

I've read Ianto's book and I thought for sure there was a place where it said to make sure the exhaust came out at a certain height in proportion to the burn tunnel's height. I've been scouring the book and can't seem to find anything. Maybe I read it here somewhere. Or am I making this up in my head? I'm wondering because the area I'm putting the stove would make it so the exhaust comes out several inches lower than the height of the burn tunnel, proportionally. I just want to make sure it's not going to hinder the air flow, etc. Do you have any experience or have heard anything about this?

When you say exhaust, are you referring to the exhaust to the chimney or the exhaust to your mass bench or whatever?

The exhaust, as in, going out under the barrel and into the heat mass. So the pipe going through the heat mass would be lower than the stove (including the burn tunnel) until the end of the pipe, where it would turn up and come out like a "normal" chimney (at this point, higher than the stove).

Our experience was that something like this doesn't work very well. The exhaust wants to rise, not be directed down. May I suggest a bell and then a bench?

Well, i'll back up Cindy's comment, it doesn't work very well, unless you keep some heat to power the chimney at the end of the mass, and you have a proper chimney.

Hi Bethany; How much lower are you talking? the top of my mass pipe is probably 4" lower than the bottom of the burn tunnel and it works with no problems. I will say that i have a rather large horizontal transition area , that max described as a mini bell when i posted pictures during my build. Do you have a nice tall vertical chimney at the end of your mass ? I believe that a tall chimney with a good draft really helps to keep exhaust moving in the right direction. One thing that i have noticed is the ease of relighting my rmh. After your mass is totally dry it should have a wonderfull draft once you have fired it up for the season. I can't get my long lighter to light if i hold it down at the burn tunnel height, i have to start it up in the feed tube then drop into my paper & kindling ! Keep at it ! building a rmh will be one of the most satisfying things you can do ! Tom

thomas rubino wrote:Hi Bethany; How much lower are you talking? the top of my mass pipe is probably 4" lower than the bottom of the burn tunnel and it works with no problems. I will say that i have a rather large horizontal transition area , that max described as a mini bell when i posted pictures during my build. Do you have a nice tall vertical chimney at the end of your mass ? I believe that a tall chimney with a good draft really helps to keep exhaust moving in the right direction. One thing that i have noticed is the ease of relighting my rmh. After your mass is totally dry it should have a wonderfull draft once you have fired it up for the season. I can't get my long lighter to light if i hold it down at the burn tunnel height, i have to start it up in the feed tube then drop into my paper & kindling ! Keep at it ! building a rmh will be one of the most satisfying things you can do ! Tom

Thank you so much everyone!

Can someone send me a link about a bell? I've tried to search around before but I can't find any information on them. I've heard OF them, but really don't know what they are or how they work.

Tom. Thanks for your encouragement. I've been researching a lot and I've been scrounging for materials. I'm almost ready to build a mock up and I'm so excited!! I'd have to go outside to get an actual measurement, but the drop would probably be about a foot lower than the burn tunnel. The plan is to build the mass into the floor so that's why there would be the drop from the stove at floor level. There is an ever-so-slight mention of this in Ianto's book, but he doesn't seem to go too in depth. It's for a greenhouse, so if I needed to I could dig down and put the stove lower as well - it would just be a little more difficult to work with. I'm going to experiment on the chimney at the end of the mass, but at this point I'm going to start with 8' I think.

http://www.stove.ru/index.php?lng=1&rs=16.

Thanks you guys! This is a neat concept. It seems like it would help make it even more efficient. I'm surprised more people don't seem to use it. I can't find anywhere though how a person would attach it to a rocket stove. Am I right to guess that this would be directly next to the rocket stove to take the gasses in? The other thing that doesn't seem clear is...wouldn't this mean the exhaust would come out quite higher? It seems it needs to be vertical for the gasses to rise properly, but then it would exhaust at the top of the barrel or bricks (or whatever the bell was made of).