Hello! I'm new to Permies. I spent over 3500 dollars on propane last winter so I decided to heat with wood for this next year. I have been wanting to build a RMH for the efficiency and I have an existing chimney hook up in my walk out basement (where an old wood stove was years ago). The house is a total of 1300 square foot and the walk out basement covers 3/4 of the main floor above. I'm wanting to build the RMH and allow the radiant heat to rise into the upstairs through floor vents just like the old school wood stoves in old farm houses. I have enough room to build a large mass but I'm concerned if the RMH will produce enough heat for the square footage. Does anyone have any thoughts? What's the largest square foot house that RMH have heated? Anyone built one in a basement for this purpose? And thoughts will be much appreciated! Thanks
Hi Jason, Welcome to Permies. Installing a rocket mass heater (rmh) in a basement is a commonly asked question. The answer is usually "not recommended" because its the type of heater that requires attention. (Less so if you were to install a batch box heater but thats something usually for a second build).
In other words, unless you spend quite a bit of time down there already, its gonna get old real fast making the journey up and down the stairs to feed the fire.
Also, being so low in the building, some issues with negative pressure may cause smoke to travel in reverse thinking that your house is a chimney instead!
All of this and more can be found in the Rocket Mass Heater Builders Guide and if you do a search in this forum, there has been conversations about this also.
For sure you'd be looking at making an 8" rmh.
posted 3 weeks ago
This is a short video of the layout of the house. Only about a 3rd of the basement is inside a hill, leaving 2/3rds exposed. So it's not a true basement.
posted 3 weeks ago
I don’t really know much about house installations but I think you might be better off looking into batch box design and bell heat distribution.
That design will possibly be more suitable but I think you will need to do extensive revision.
RMHs provide a lot of heating through conduction and radiation, so if you are in the same space you get the best results. Convection also happens but to a lesser extent. My main experience with RMHs was spending about 10 days at Cob Cottage where the Myrtle (library) was running the RMH each night around dinner time for say 40 minutes, and that was it. In the morning it might have been 38-40F degrees per the outdoor thermometer, but you'd step inside Myrtle for breakfast and this wall of heat would greet you at the door.
That space was essentially one room, so most of that could have been radiant heat. But as several of us were moving around, you never felt like you do near a fire, where the side facing away is cold. The Myrtle is a totally cob structure, so that big thermal mass would absorb RMH radiant heat during the evening and solar radiant heat during the day through passive solar design. So perhaps that balanced the heat we felt in the morning. The day would warm up to 50-55 but the house was always very comfortable. All that said, heating the basement up nice and toasty would certainly happen, but if the foundation isn't insulated on the outside then the walls would be a heat sink and rob some/a lot of the heat. Meanwhile the wooden floor joists and framing aren't going to conduct as much heat up, and some convective heat can travel up the stairwell but I doubt it would be enough for the rest of the house.
If you can use waste wood to run it, then the RMH would probably lower your heating bill, but probably not eliminate it.
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