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rocket mass heaters

Exit flue in bell bench

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posted 3 months ago

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So I have planned to have my stratification bench at around 16" with 4" of cob on top. That leaves 12" of void so my question is... If my 6" flue is horizontal on the floor is that effectively reducing the ISA by half? I don't think it would be too difficult to scoop out another 6" for the flue to sit in if it is worth doing. Or would the gasses still have time to absorb into the wall before leaving up the flue?

R Scott

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Location: Kansas Zone 6a

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posted 3 months ago

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How long is the bench?

Are you pulling the exhaust from the far end? (guessing because of the horizontal pipe) You could add an HVAC register boot to pull from closer to the floor, but I don’t know how much restriction that would add.

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Mike Schofield

Posts: 52

posted 3 months ago

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The bench is 8' long and 17" wide, internal measurements that is

Mike Schofield

Posts: 52

posted 3 months ago

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The exhaust is same end as the manifold. I will extend the exit flue 20" or so into the bench however as I am worried about sucking the hot gases straight from the manifold if the chimney is drawing strongly

R Scott

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Location: Kansas Zone 6a

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posted 3 months ago

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If that case, if it were me I would either….

I would turn that elbow to something like 75 degrees and cut a long angle on the pipe so the opening sits about 3 inches off the bottom (a little room for ash buildup)

Or

Put a pipe on the manifold so it dumps the hot air towards the middle of the bench

I just started a build and have the same dilemma. I am going to choose one of those options depending on which looks easier to fit once I get the manifold in place.

Mike Schofield

Posts: 52

posted 3 months ago

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My latest idea is to cut a channel the length of the bench at the same proportions as the heat riser and cover with bricks as in the bridge, with the gasses exiting the bench at the opposite end to the manifold. This should give to heat every chance to rise and absorb into the brick work and hopefully gain more ISA.. Good idea/bad idea?

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R Scott

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Posts: 4024

Location: Kansas Zone 6a

284

posted 3 months ago

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I like it. You just gave me a third option.

You may need to oversize that trench slightly depending on drag, but I don’t know for sure.

Mike Schofield

Posts: 52

posted 2 months ago

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So I decided I would go with the trench idea. It's oversized as you suggested at around 8x8". A bit over to be honest. I'm now wondering whether to leave it as is or maybe skim to inside smooth. I was thinking of a perlite/lime/cement mix to insulate it a bit too.

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