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Hooking a RMH up to Existing Stove Pipe  RSS feed

 
Jerry Ward
Posts: 191
Location: S.E. Michigan - Zone 6a
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A lot of what I read has the RMH exhaust going out through a side wall of the house. I'm in a position where I may need to install wood heat now in new construction in Michigan. This will involve something like 36' of triple wall stove going up through the roof with a wood stove attached to it for now. I would like to try switching over to a RMH in a year (or three or five at the rate I get projects done) and wonder if there will be a problem using that existing stove pipe.
 
Mark Heffernan
Posts: 11
Location: Richland Center, WI
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I have a similar situation to Jerry's and also want to know about using an existing chimney. In my case the chimney has two flues that are about 8" x 12" and 30-40- feet tall from the basement ground level. The flues are surrounded by brick with an air space in between the two materials. I would like to use one of the flues that had previously been used for a wood stove, but that flue has lots of creosote from poor use of the old system. In fact, there is so much creosote that it has gotten between the flue liner and the brick, so I have not used the flue in 15 years. I was thinking that a RMH would be able to be vented to this chimney due to the elimination of the creosote forming gasses in a clean burn and due to the much lower discharge temperatures by the time it vents to the chimney. The chimney draws well right now from the room temp air (60-65 degrees) to the 20-30 degree outside temps from the 6" or the 8" flue openings into it at the basement level. Perhaps that draw is also good due to the fact that the second flue in the chimney is receiving the vent from the parlor gas heater on the second story. Any thoughts?
 
Ernie Wisner
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Location: Tonasket washington
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for both of you plan on 8 inch systems. no problem going out existing pipe/chimney. for the brick chimney figure 200 degrees will be needed to heat all that mass and provide rise for the exhaust. for the trip wall figure 100 degrees for lift. neither of you should have much problem. the 40 feet up is not to bad.

What i would make sure of is that you have a shallow incline to the exhaust so everything is generally up for the exhaust gasses. I would limit my pipe run to the chimney to about 30 feet and make a nice tall heat riser with a very short burn tunnel. you will want as much air speed as you can get (very rockety). plan to add lots of thermal mass and make a plan that you will add the mass till your temps are as outlined when the stove is running at full burn. temps should give you a bit of leeway.
 
Jerry Ward
Posts: 191
Location: S.E. Michigan - Zone 6a
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I will have a 6" stove pipe, 8" really isn't an option. I know that means I need to design my RMH for 6", is there any other big issues?
 
Ernie Wisner
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Location: Tonasket washington
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not really just the usual of make as much thermal mass as possible for heat storage and locate the stove as close as you can to the center of the house.
 
dave marth
Posts: 50
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Hello everyone, im new around here...just thought I'd jump in a little late on this one and ask a question about the basement location. Do you feel that a roclet mass heater will heat a 1000sq ft ranch home with a 700 sq foot basement? I had a wood stove down there last season as well and it heated the entire house very well. Just dont know if the heater puts out heat enough to heat the basement and upstairs. I also have a 6 inch chimney in the wall going up 18' high. I live in PA just below the poconos 30 miles east of NJ. I would prefer making my mass out of rock and other non-permanent material unlike cob. My basement is concrete woth asbestos tiles.
 
Erica Wisner
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Location: Okanogan Highlands, Washington
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Dave Marth - most likely an 8" rocket mass heater would do the trick. Not sure about a 6".
Little-known secret for those with an existing 6" chimney:
You can build a 7" system and taper gently to a 6" exit if you do it after about 20 feet on into the heat-exchange area. The exhaust is cooling and condensing by this time, and can flow through a smaller space. We don't usually go into this on first-time builds, as people get ambitious and screw up other flow areas that should be preserved intact.
(This is for solid mass heaters, not sure about the 'loose rock' variety which I don't endorse indoors, see below.)

I have a couple concerns with any basement build:
- is this basement a place where you spend time, like a rec room or home office? Unattended solid-fuel heaters aren't a great idea, and if nobody is in the basement you lose the conductive heat benefit which is a factor in the RMH's efficiency. You will be burning more wood than someone who can sit on their heater. These are not a 'light it and leave it' device, though they are relatively low-maintenance if you are just hanging out in the same room and doing other things.
- make sure there is not a negative pressure situation with the home drawing hot air out the roof vents, and making any basement opening into an air intake. Using an existing tall, warm, indoor chimney rather than a side vent is likely a very good idea for a basement installation.

- non-permanent thermal mass like rock:
Non-permanent is fine. Non-sealed is not such a good idea. We rely on cob as a secondary seal around the ductwork, to make sure no smoke or exhaust can escape into the room, AND to ensure that in the event of a creosote problem, there would be no adverse effects from a (improbable) chimney fire in the horizontal flues.
Cob is also non-permanent; one option would be to cob directly around the pipes for a seal / better heat conductivity, and then dry-stack the remaining rock or brick to make it much easier to remove later.
Brick with lime mortars is also easy to remove again (though caustic when fresh), and offers a decent secondary seal in the low-temp bench area.

You can do a secondary seal some other way - stove cement or foil tape around the joints, for example. Just be sure it's good and sealed, and if any pipe is exposed to room air consider stovepipe in that area, not galv. ducting.

Yours,
Erica W
 
dave marth
Posts: 50
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Thanks Erica for the reply. The basement is not often used to gather, more so to do laundry. I have a Big Moe wood stove, very high quality from Vermont Castings, but more efficient is what draws me near as with everyone. That is located in the basement and radiates at about 500°f on the stove top. Plenty to heat the basement, rise up the stairs and float around the upstairs after a few hours. But it requires lots if loads of wood. Wouldnt the mass down in the basement radiate as much since its nit as hot? I know the barrel is for fast heat pumping but afger that fire burns out then will the bench fill the rest of the house with warm radiant air? I dont think installing one upstairs is an option...
 
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