6" RMH Build

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Re: 6" RMH Build

Postby mannytheseacow » Sat Jan 18, 2014 7:12 pm

We had another week of single digits this week and gosh I'm tired of a 60* house. I disconnected the RMH today and subbed in the old pot belly, just for a little assessment. One load of wood through it (3- 7"rounds, about 50#) and an hour later my house was 20* warmer, not to mention the heat coming off that thing was almost instantaneous! It was great, I boiled some water, cooked some pork and beans, and still threw a ton of heat out there.

Watching that thing burn got my wheels turning. There's been a lot of talk about my big 'ol bench and my 6" RMH, and I'm sitting there looking at these two heaters that both have issues and noticing that they are on two extreme opposite ends of the spectrum. What would my ideal heater be? Well, burn bigger pieces of wood, allow more instant heat, but still have the ability to store that heat for a slow release (though not as slow as I've got now). Looking at my big old bench I'm realizing that this big old mass is more of an insulator than a battery.

I currently have 2 thoughts. One is that a cooking heater for my upstairs would be great. It needs to offer quick heat, not big storage, and I have a very limited amount of space to put it in. My concern is that even with this extra heater upstairs it may not address the whole house warmth issue. I posted somewhere else recently about my air exchanger and that is helping circulate the heat, but the fact remains that there just isn't enough heat. So my second thought is that my project this summer might be to take a pick and shovel to the 6" RMH and convert it to an 8". I think trenching the pipes through the bench will be fairly easy, it's converting my chimney to 8" that will be the bigger challenge, but it can be done. The chimney is actually a 7" square column that I have lined with a 6" stove pipe. It would be perfect for an 8" system. But I hate messing with chipping rock and there will be quite a bit of that to do to get an 8" opening, not to mention pulling the lining and having to replace the pipe through the roof. This seems like the best option, though. And I can use all the lining to build the upstairs cook stove. Anyone got an idea for a J to cook on that will fit in a space 16" x 36" x 30"?

In the meantime the RMH is back connected and storing all its heat from the little sticks that it's burning. (sigh)

I'm gonna go eat some pork and beans. Then maybe go snowboarding.
"Knowledge is power. Arm yourself."
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Re: 6" RMH Build

Postby pa_friendly_guy » Sat Jan 18, 2014 7:36 pm

I am glad that you are getting enough heat out of the old pot belly to keep warn Manny. Trying to heat your house with that small 6" unit is like trying to steer the Queen Marry with a row boat. Its seems to be just too small to get the job done. Changing over to an 8" system should get you a lot more heat, as well as heat up your large bench for a good fly wheel effect. Since you are not looking for a large thermal mass in the up stairs unit, but cooking seems to be on your list of used for the heater, why not try a small Box Stove with 2 cast iron burners on the top. They are inexpensive, put out a lot of heat instantly, and you can cook on them. Spacing and clearances to combustible walls, floors, and ceilings could be a concern with your tight spaces, and they are not truly air tight , and they are not very efficient, but for what you want to use it for a small Box Stove might just be the ticket. They can take the chill off things, heat up a bowel of soup or a stew. I don't think you could get a fire to last through the night, so it might be a bit chilly when you wake up, oh well, can't have everything in a cheap heater can we?

http://www.northerntool.com/shop/tools/ ... 054_346054

Here is one example of what I an talking about. I have seen smaller units for less than $200. You can try and line the unit with some fire clay or sand to keep it from burning out.
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Re: 6" RMH Build

Postby mannytheseacow » Sat Jan 18, 2014 7:42 pm

Yeah, part of me was thinking just to put the old potbelly upstairs, but I'd like a bigger cook surface and it's just a little too big and makes too much heat. Sheesh! Picky picky. :lol:
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Re: 6" RMH Build

Postby matt walker » Sat Jan 18, 2014 8:14 pm

Dang, I wanna go snowboarding. It's 50 here. I think I'm gonna pressure wash the roof. :(

On your proposed modification, I would probably start with upping the system size to 8" without changing the chimney and see what happens. If you take enough heat out theoretically the gases will condense quite a bit so it might just work. I know I've read of successful builds that do exactly this, but it's all so specific to the build that the only way to know if it will work for you is to try it.
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Re: 6" RMH Build

Postby hpmer » Sat Jan 18, 2014 8:54 pm

And if there's still too much heat it might be easier to add more mass or a bell than mess with the chimney.
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Re: 6" RMH Build

Postby mannytheseacow » Mon Jan 20, 2014 3:31 am

That being the case, would it make sense to start by running 8" lines through the bench and see how it does with the. 6" core to start?
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Re: 6" RMH Build

Postby hpmer » Mon Jan 20, 2014 2:48 pm

Certainly wouldn't hurt to do it in stages, but I think your issue is not enough output from the core.

A 6x6" core is 36" csa, while an 8x8" is 64", almost double the output. THAT is where you're going to see the big improvement.

Of course, if you're going with 8" pipe in the bench, rather than 8" square channels, you'll be slightly less than an 8" square core, but still, you'll find the improvement surprising.
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Re: 6" RMH Build

Postby matt walker » Mon Jan 20, 2014 4:48 pm

I agree with Hpmer. It would work fine with larger flue in the bench, but you need more BTU's than you can run through that little feed.
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