Hello... and a question

[matthewwalker]

Hi folks. I wanted to say hello and thanks for this gathering of minds and information. Very, very informative.

I built my first RMH prototype in my shop this weekend, a 6" system, and am hooked! I'm interested in getting one in the house ASAP, as I heat solely with wood and currently burn >6 cords a year. I'd love to reduce that!!

So, my planned install is an 8" system, about 30ft of horizontal ducting in a cob bench, and then tie into the existing chimney. My question, well, I guess I have two:

First, if I use 8" stove pipe for the heat riser, with a 10" sleeve with pearlite/clay slip insulation, will a 55 gallon drum be too large of a barrel for this system?

Secondly, I read the thread about tying into an existing chimney, and the concerns of some of the responses weren't clear. What, other than achieving adequate draft, should I be concerned with in such an install? Existing traditional stove uses 8 pipe to the wall, which then interfaces with traditional 10" sleeved chimney, which also services a oil furnace (unused, but still functional, I'd like to keep it that way if possible) a floor below in the basement.

Thanks so much for the great info everybody!

Matt

[peterberg]

Hi Matt, welcome to the board.

Dec 5, 2011 16:25:00 GMT -8 matthewwalker said:

First, if I use 8" stove pipe for the heat riser, with a 10" sleeve with pearlite/clay slip insulation, will a 55 gallon drum be too large of a barrel for this system?.

Two remarks: an 8" stove pipe as a riser won't serve you long. Especially the lower end of it will burn away in a season. It will get awfully hot there, together with a very low CO level. These combined conditions will extract carbon out of the metal, turning it into rust.
One inch of perlite/clay as insulation isn't adequate to keep most of the heat in. You are running the risk of not enough temperature difference between the inside and outside of the riser, which will stall the draft eventually.

Please do build the riser out of fire brick and as much insulation as is possible to stuff in there. The insulation canister can be made out of another 55 gallon barrel. Cut off the bottom and top rim, cut it vertically and fold it into a smaller barrel. Fix it with small bolt and nuts or steel rivets.

Dec 5, 2011 16:25:00 GMT -8 matthewwalker said:

Existing traditional stove uses 8 pipe to the wall, which then interfaces with traditional 10" sleeved chimney, which also services a oil furnace (unused, but still functional, I'd like to keep it that way if possible) a floor below in the basement.

As far as I can see, nothing wrong with 8" pipe and 10" chimney, provided the chimney is inside the house envelop. Outside chimneys in a chase are notoriously stubborn.

The oil furnace in the basement is a negative fact, though. Apart of leakage from the basement, the several feet down of empty chimney with stalled air is generating drag onto the chimney above it. Perhaps you are able to alleviate that with a damper about one foot down from the rocket's entry in the chimney?

[matthewwalker]

Thank you so much for the response, I very much appreciate the feedback. Great tip on the heat riser. I will follow your advice there for sure.

The chimney is inside the house, except for a brick stack on the roof about 5 feet high. It's not accessible from below, but perhaps I can plug it below the rocket's entrance with a piece of concrete backer board or sheet metal or something.

Thanks again!

Matt

[pasto76]

Im also wondering how big is too big or too small for the bell? I plan on using 6" riser inside a bolt keg that is 27" tall and 14" across. Ive calculated the gap required from top of riser to the bell, but how much of a gap should I have along the sides? a 55 gal drum would be too big? I would prefer to build the bell out of brick, so I can make it optimal, if there is an optimal. Thanks

[matthewwalker]

The book calls for 1.5" clearance all the way around from heatriser to barrel, but it seems the consensus is bigger is okay.

[peterberg]

Dec 15, 2011 21:12:11 GMT -8 pasto76 said:

I'm also wondering how big is too big or too small for the bell? I plan on using 6" riser inside a bolt keg that is 27" tall and 14" across. Ive calculated the gap required from top of riser to the bell, but how much of a gap should I have along the sides? a 55 gal drum would be too big? I would prefer to build the bell out of brick, so I can make it optimal, if there is an optimal. Thanks

It all comes down to this question: do you want to build a bench as mass storage? When the answer happens to be "yes" it's best to maintain a gap of 1.5" or 2". And having a steel barrel around the riser will make it easier to keep a temperature difference between the inside of the riser and the inside of the barrel.

However, when the answer is "no", and you like to build a brick bell construction, there isn't such a thing as a gap. Only a lot of wall area enclosing one or more volumes. So the gap above the riser is irrelevant in this respect as well. I've done several experimental stoves which had a top "gap" of 3' to 5'. That bell was acting as a barrel and bench at the same time.