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Post by pelidc on Feb 3, 2019 14:25:58 GMT -8
Details on my house: -Northern MN, temps this winter have gotten down to -60 F with wind chill -About 3k sq ft, single story with nearly full basement -Basement is concrete floor with radiant tubes, poured concrete ICF walls. Intending to finish basement off. -Chimney is new construction, clay liner with insulation wrapped around inside concrete block, extends a couple feet past roof peak -Chimney stub is in basement, 9" diameter pipe. Total height of chimney from stub is probably around 22', about 2' of which is below grade Would like to build a j-tube with 55-gal with brick-wall-contained pea gravel for mass, exhaust tube extending maybe 10' to one side before turning back and rising to chimney. In my reading on this forum and others, I've read that it's generally not advised to build these in a basement due to stack effect disrupting draft. Also problems with cold chimneys. My thought is that pea gravel won't absorb as much heat as cob so it might not have problems with draft, especially since chimney rises above peak. Wanted to see what you guys thought about whether the situation is too problematic for a RMH? Will I need insulating blanket under burn chamber to protect in-floor pex tubes? Will I have to have a 9" diameter throughout the system to match chimney stub? Any other issues you can point out? I've already spoken to our insurance inspector, he said that my design had the proper clearances, and since we have a CO monitor down there and additional heat sources, he'd approve whatever I build. I've attached the design I sent him, I've also got a couple pics of my house. Let me know if I can provide any other info/pictures. PICS
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Post by wiscojames on Feb 3, 2019 17:02:38 GMT -8
I can't see your design, only 2 pix of a house and whag looks like a wall in a basement.
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Post by pelidc on Feb 3, 2019 21:30:37 GMT -8
Not sure what the problem is, pics are coming up fine on different browsers for me. Can you give me an estimate based on the info alone?
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Post by Dan (Upstate NY, USA) on Feb 4, 2019 4:56:15 GMT -8
Make sure to have an airspace to build above in order to make sure you do not burn your PEX.
Same thing is done a lot for building above wood floors...
Like bricks on their sides with a slab on top to ensure air flow below/under the heater so you don't pop your PEX....
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Post by DCish on Feb 4, 2019 10:05:09 GMT -8
Ditto on the air space below your heater. Insulation slows heat transfer, but doesn't stop it. If you don't have a way to carry the heat away (e.g., free air flow under the heater), the heat will eventually transfer through.
Another thought -- do you plan to spend a lot of time in the basement? J tubes need frequent tending, so if you plan to be in that space constantly, you'll be fine. If you will spend more time in other spaces, you may want to consider a batch box.
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Post by pelidc on Feb 4, 2019 14:17:57 GMT -8
I do plan on spending a lot of time down there, so that won't be a problem. Thanks for the tip on the air gap, I'll be sure to incorporate that. No concerns with the stack effect and cold chimney? Will I need to maintain 9" diameter?
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Post by DCish on Feb 4, 2019 15:21:43 GMT -8
I do plan on spending a lot of time down there, so that won't be a problem. Thanks for the tip on the air gap, I'll be sure to incorporate that. No concerns with the stack effect and cold chimney? Will I need to maintain 9" diameter? Sorry, I don't have direct experience on the last two. I do know that a cold chimney is harder to start and may need more leftover heat to run properly. It may also need to be primed to get draft going, whether you use a bypass to help get it going, or whether you use a bit of newspaper lit in a cleanout at the bottom of the chimney. As for the 9" diameter, that I know even less about. My best guess is that it would once again increase the amount of heat required to run it effectively. So you have a few dings against efficiency in your build. Personally I'd be tempted to do some prototyping to see how it goes. A J-tube has less power output than a similarly sized batch box, so I'd be tempted to do an 8" J build. That gets you closer to your chimney size, and I doubt you'd be overwhelmed by the heat output. Also, don't feel wedded to making your bench have channels. A dead-end bench is a very efficient heat harvester (that's the kind I built), and heats more evenly than a bench with channels. Best of luck, and keep us posted!
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Post by coisinger on Feb 5, 2019 4:55:14 GMT -8
Channel flow pipes with gravel are mostly a thing of the past for RMHs. They need to be constructed well with flow in an upward path and the fill material needs to be non-insulative. Air gaps using gravel beds will reduce performance.
You will save yourself a lot of effort and time by building an open bench, as DCish has suggested. The bench will still radiate heat long after the the fire is gone. Use a solid masonry product, brick without cores or be sure to fill cores completely, to maximize the heat transfer and radiation after.
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Post by michaelegan on Feb 12, 2019 18:58:51 GMT -8
Would it be possible to put a round liner in your tile flue? That should help your draw. Ceramic liners take a while to heat up. I built a 26' masonry chimney in my shop 12 years ago just before I learned about rocket mass heaters, built and ran an 8" j tube for a year, then a batch box for 5. The 8" square chimney was ok but i put an 8" round stove pipe T in and always primed it with a little fire which lasted maybe 2 minutes. So I didn't do what i'm suggesting but would have if we hadn't moved back to our farm in central illinois.
Regarding storage i am totally in favor of bells which in your case could be the hollow bench that was suggested. They are easier to construct (a hollow box), less to no maintenance, work better, I also think they improve the draw since there is almost no friction.
Personally, I have become a big believer in the batch box, following Peter Berg's models, using ceramic glass for a nice visual either on the door or side of the burn chamber.
Best of luck on your build! I'm guessing you will be happy with it and if you're like me your understanding of fire and the benefits of these systems will truly enhance your life and clean up the air for you and those nearby.
Keep us posted on your work.
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Post by michaelegan on Feb 12, 2019 19:15:57 GMT -8
Is your liner 9" round inside diameter? If it is you should be able to slip 8" round pipe into it from the top. I have an 8" batch in my pole barn with an 8" chimney, most of which is cheap galvanized thin wall heating duct from Menards. The bottom 5' or so is black stove pipe out of the bell but in your case you could feed 6' lengths down from the top and keep attaching the next 6' section with 3 zip screws until you got to the thimble, then either put an elbow on or use mortar/cob/etc to form a seal. You could also pour some perlite or vermiculite in the gap but I probably wouldn't bother since you'd have a dead air space which would help keep your flu warmer. The heating duct is galvanized which will burn off at 700 degrees F: your temperatures will likely be 150-300 F max.
I cut a piece of the same duct and fashioned a cap, barrel vault shape also screwed a piece of steel lath onto the opening to keep birds and squirrels out. After a year, has worked very well.
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Post by Orange on Feb 22, 2019 11:41:00 GMT -8
michaelegan interesting, what was the warmup time for ceramic flue and is there a significant difference in draw with the low-mass chimney? I think it's safe to use galvanized pipes as a boiling point of zync is 907 °C, 1665 °F. pelidc that is a 278m2 house you wat to heat? I'd put a 9-10" BB
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