length of exhaust pipe

I'm considering building a rocket stove mass heater inside an attached 2 car garage and running the exhaust pipe and cob mortar bench under the house. The space under the house is 50 feet long X 30 feet wide X 3 feet high. My plan is to run the exhaust pipe surrounded by cob under the full length of the house, make a wide u-turn with the exhaust pipe and run it back the the full length of the house again, then out through the side wall. This would make the overall length of the exhaust pipe about 120 feet. My idea is to install a few vents in the floor of the house so that the heat from the exhaust and cob bench under the house will rise through the floor vents and heat the house. I would like to get some input about this idea, especially about the length of the exhaust pipe and the radiant heat rising from the mass of the cob bench which would be around the exhaust pipe under the house. By the way, the crawl space under te house is insulated.

Chris Evans : build 50 feet with 8'' pipe, and try that, then see if you want to add more ! The only reason to heat an insulated space is because you want to live there ! Are you telling me that The side walls of your 'crawl space' are insulated and the underside of the floor is not ? Which will work - Or the other way which will make a good place to grow mushrooms ! Where is your vapor barrier located ? Do you have Ianto Evans' book 'Rocket mass heaters '?


Be safe - Keep warm , PYRO -Magic-ally yours , - Allen L.

There is a ground cover on the ground in the crawl space, the walls of the crawl space are insulated and the floor of the house are insulated. My plan is to cut rectangular holes all the way through the floor of the house so that warm radiant from the exhaust pipe and cob bench under the house will rise through the vent holes in the floor of the house and heat the house. Is there a reason that you think that an exhaust longer than 50 feet won't draw well?

chris : Just doing 50 feet is a very challenging project, It is pretty important that you be a little conservative on your 1st build,

+ 50 feet is do able depending on how much heat you end up extracting from your pipe into your thermal mass, it is possible to lower the temperature of your exhaust gases in your horizontal pipe that it would draw in
any chimney, insulated or not , then you are stuck running a horizontal chimney only,With the strong possibility of poor draw when the wind shifts to 'that direction !'

Someone was concerned enough about creating water vapor problems in your 'crawl space' to put down some kinda water vapor shield which is probably plastic and will melt ? Try an extra scrap and see if it will burn ! Can you be sure that during spring run-off the water table will not be close enough to the surface that you adding heat down there CAN NOT turn your 'crawl space' into a sauna ? ++

get a second opinion before you go on farther Allen +++L.

chris : Just doing 50 feet is a very challenging project, It is pretty important that you be a little conservative on your 1st build,

+ 50 feet is do able depending on how much heat you end up extracting from your pipe into your thermal mass, it is possible to lower the temperature of your exhaust gases in your horizontal pipe that it would not draw in
any chimney, insulated or not , then you are stuck running a horizontal chimney only,With the strong possibility of poor draw when the wind shifts to 'that direction !'

Someone was concerned enough about creating water vapor problems in your 'crawl space' to put down some kinda water vapor shield which is probably plastic and will melt ? Try an extra scrap and see if it will burn ! Can you be sure that during spring run-off the water table will not be close enough to the surface that you adding heat down there CAN NOT turn your 'crawl space' into a sauna ? ++

get a second opinion before you go on farther Allen +++L.

I appreciate your concerns and the information you've share. Excellent things for me to consider in the planning and construction process. I'm actually planning to build a less extensive RSMH project before I tackle the crawl space project. In The crawl space however, I was planning to put a gravel and rock base between the plastic ground cover and the exhaust pipe. The other point you made about the snow and spring run off is a good point. Even though we had a record snow winter 2years ago, I have been under the house many times and I have never seen any evidence of water standing. I believe the reason the plastics ground cover was installed was because many finance companies require it. I like your advice about trying a 50 foot run of exhaust pipe first to see how it draws. An excellent idea and one I plan to use when the time comes. Thanks for your help.