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John Derry
Posts: 45
Location: County Kerry, Ireland
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Having read and listened to much about RMHs,  I am at the point where I need to build one in time for winter.

I plan to mostly follow Erica and Ernie's 6" annex design (possibly with an insulated brick heat riser), though part of me feels I've read so much now I am delaying myself by overthinking the many options.

From a dual wish to save money and placate building regulations, may I have people's opinion on the suitability of using firebricks (photo attached of surplus stock a local guy has), instead of reclaimed red brick (which is quite expensive around here)?

As I am struggling to find any 2nd hand stove pipe here in Ireland, and having read the bendable ducting stuff creates too much air drag, does anybody have any suggestions for cheaper alternatives to brand new stove pipe?

Many thanks,
John.
 
allen lumley
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Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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John Derry : Depends totally on you! If a friend has free or cheap brick by all means use that. You may find yourself wondering why you didn't save some for

The next guy! You may decide to help a new rocketeer out and swap fire bricks for something else. Remember every thing that is not combustion core can

certainly be build with nearly any dense non porous materials. I would not recommend shale or mud stone, Slate should work a treat ! The more solid material

you include the less cob you have to make !

The type of reclaimed brick you want kinda falls into a middle grade between soft lightweight fire brick and Hard Dense Fire/kiln brick it is dead soft

leaving a mark behind when rubbed on concrete /pavement.

Here in the States most of the houses are heated with Fossil Fuel Fired Forced-air Furnaces, This often translates to a complete scraping and Total

replacement after a fire, I have had great luck finding a fire damaged house -look-for boarded up windows and a huge skip/dumpster out in front ,

sometimes I am Dumpster-diving, sometimes I am invited in to go for the Forced-air ductwork. As Forced air is retarded and more trouble than its worth-

I Understand it is very rare on your side of the Atlantic. Demolition crews rarely if ever save old piping and you are using it inside your Thermal Mass Bench

as forms -for you longevity is not an issue. keep looking ! Big AL
 
John Derry
Posts: 45
Location: County Kerry, Ireland
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Thank you Allen.

Central heating here is nearly always water filled radiator's connected by 15/22mm copper pipe, the contents being heated by a boiler and then pumped around. So, it does seem likely that brand new stove pipe will be needed. The pipe alone will be many hundreds. I wondered if metal air ducting would be of sufficient heat resilience, perhaps after a certain run past the manifold?

The cheap (only due to random surplus) fire brick looks like this: https://www.dropbox.com/sc/ya4br0utj3havxg/AADrdEfQdHvD4Kooev3fSlyRa. I'm somewhat sure I'll be able to work out how to use the odd dimensions to make the needed channels, but wondered about it having the right heat tolerance's and performances - I read a previous post of yours that said that some fire brick is fairly poor for this job.

Many thanks,
John.
 
allen lumley
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Posts: 4154
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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John Derry : Measuring from where the rapidly falling gases turn 90º to start flowing horizontally, 1 meter of stovepipe should be enough to cool your

Exhaust gas temps to take any kind of pipe you can find.

I am unsure what the problem might be with firebrick, There are two kinds of furnace cement one cures with a soft set and the other cures so hard that

The fire brick becomes locked together with no room for expansion, this can cause the brick to crack , fracture or spall with both small and large pieces.

I have had good luck with just using a homemade clay and sand mortar. Mortars primary job is not to bring the bricks close together, rather the mortar

is used to hold the bricks a set distance apart to help make each course Level and Plumb. Perhaps improper use of Hard setting Furnace cement is the

cause of the problem and not the bricks ? For the Good of the Craft ! Big AL
 
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