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rocket mass heaters

Mass heater exhaust runs

Posts: 33

posted 10 years ago

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I've heard of 50' for an 8" run with 5' for each 90* elbow. Was wondering about how long you can run 6". I'm going to build one but I have to tie it in to my 6" stove pipe from my wood stove. Thanks in advance.

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John Adamz

Posts: 126

Location: Springfield, mo

posted 10 years ago

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I think ~30ft of horizontal run is the consensus.
Oddly enough I just noticed that the CSA of a RMH in inches is roughly equal to the run in feet. Likely pure coincidence, but I'm a geek for numbers

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Satamax Antone

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Location: Southern alps, on the French side of the french /italian border 5000ft elevation

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posted 10 years ago

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Quoted from Ernie.

Well a 12 inch system will go about 100 feet a ten inch about 75 feet and 8 inch about 50 and a six inch about 45 maximum.

Remember that absolute maximums.

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Jimmy Smith

Posts: 33

posted 10 years ago

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Thanks for the info. Starting to put the pieces together to build one. I will eventually buy the book or the DVDs once all of the winter bill are caught up, our power bill up here has gone up to $300 a month and I heat with wood. It's been a long one this year.

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John Adamz

Posts: 126

Location: Springfield, mo

posted 10 years ago

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Satamax- Thanks for posting that concise info from Ernie. Don't think I have seen it before. Should make it easy for others to find now if searching for exhaust run lengths.
After my crazy numbers observation, all but the 6" in Ernie's recommendations fit my hypothesis. I still think a 6" system should be more like 35ft max.

"Necessity is the mother of invention" That's why I'm a Jack of all trades, Master of some and have learned that Knowledge is power, but information isn't necessarily knowledge.

Alan Wright

Posts: 8

posted 10 years ago

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We've got 50' with an 8 inch system. We use an in-line fan to get it going and then once its warm she runs good, except when the wind blows hard. I know its "cheating" but we love the in-line fan, takes all the difficulty out of it.

John Adamz

Posts: 126

Location: Springfield, mo

posted 10 years ago

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Alan Wright wrote:We've got 50' with an 8 inch system. We use an in-line fan to get it going and then once its warm she runs good, except when the wind blows hard. I know its "cheating" but we love the in-line fan, takes all the difficulty out of it.

While having an inline fan obviously helps with draw, if anybody decides to use one it shouldn't simply be put directly inline of the exhaust unless it's being run all the time. When it's not running it will slow/restrict the exhaust flow. There is scant discussion of an inline fan's proper placement as it's regular use is not generally recommended.
It's possible that you could eliminate the need for a fan by having a higher vertical chimney, and/or using a different chimney cap/top

"Necessity is the mother of invention" That's why I'm a Jack of all trades, Master of some and have learned that Knowledge is power, but information isn't necessarily knowledge.

ronald bush

Posts: 140

posted 10 years ago

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if you get a boost from locating the flue next to the hot barrel. wont that power additional length in the mass run? with a cut off(like the under floor experiment) to get it going, then switch to the mass run.

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