I want to built a rocket mass heater, in my exiting house with a 25-30 ft chimney. I want to use the portable rocket mass heater style design with wood sand and gravel. I want to place it on top of an existing floor. The floor has no way to get under it. No basement, no crawl space. I would make sure the thing does not exceed 2,000lb or something like that which should be possible if I don't fill in the center of my bench with gravel & sand I think i'll be ok.
The stove I want to build has 90 degree angles as described.
5 ft. (horizontal square bench.)
5 ft. (horizontal square bench)
6 ft. (horizontal square bench)
6 ft. (vert) Going up. along side outside of chimney.
1 ft 90 degree joint inside.
24 ft to top of chimney.
Attached PIC: want to put the the barrel to the right of the chimney, and build a brick wall handle the heat, where existing sheet rock it, and put the bench basically where I put the sofa in the center of the room, and then put the exuast up the left side of the chimney before entering the chimney about 6ft up.
Note: I have not lined the chimney yet, but from what I hear flex tube is not a good idea, so I'll try to find the cheapest decent way to line it. It's just brick now.
Some Questions I have: How much does code matter? I live in NY. Own my own house. I'v been looking at this forum an seeing that that RMH's are not covered under code. Now how much should I care about that? Does it only make a differences when I try to sell the house or should I care while I live in it? It is a nice house so id like to have it covered if my RMH goes wild and burns my house down. When it comes to code is it like: what the city doesn't know wont hurt them? or do you need to get every device you add you your house, specifically inspected and insured?
What would work better for this length of a system: 8" or 6"?
Size of barrel. 30 gallon drums are nice and compact, id rather use one over a 55 gallon drum. Is there there anything wrong with using a smaller barrel, on a system of this size?
But my guess is one to make the heater, give it a second 2nd skin that looks good in a colonial, make it code worthy, and poor a footing, and line 25ft of my chimney (no idea what that costs) i'm looking at $2,500 total i'm guessing).
If all else fails ill throw in a wood stove with flex pipe, and call it a day.
Any tips or guidance you might have, I thought I would bring it forth to those who have gone before, before doing something dumb, on my own.
Speaking as a certified chimney professional, building codes are established to protect homeowners from dangerous installations performed by professionals. When building anything not according to code the real issues are whether or not your insurance company will cover any damages due to malfunction. In new construction the Authority Having Jurisdiction (AHJ) may not approve such installation. Without their approval you may not be able to obtain a certificate of occupancy. That aside, building codes are no longer full of arbitrary rules. Most all code requirements are based on solid science.
I am a new fan of rocket mass heaters. The simple technology rivals and exceeds many of the products I already endorse, sell, and service. The 2 publications that most AHJs use to establish local code requirements for chimneys and masonry heaters are the NFPA 211 and the IRC. Neither of these publications cover rocket mass heaters. This doesn't mean that your AHJ will not give you approval, however, it may herald a long process to get that approval. I am not aware of any activity within the National Chimney Sweep Guild or the NFPA with regard to rocket mass heaters. The NFPA 211 does address masonry heaters, as does the IRC. A rocket mass stove is similar in some ways to a masonry heater, so, when approaching your AHJ you might refer to this related appliance.
As a professional the main question I have yet to answer is regarding clearance to combustibles from the secondary combustion chamber (the drum over the riser). The closest standard I can come up with that for an unlisted wood stove, which is 36 inches. What concerns me is the much higher temperature of the secondary combustion chamber. As I understand it, these can reach temperatures over 700° F. Wood stoves are typically operated with a surface temperature of 500° F. To me that extra 200 degrees is pretty significant. I doubt that 36 inches remains a good guideline. I also consider that the high heat that the drum must endure might burn that steel out. If there was a burn out during use nearby combustibles could be exposed to up to twice the heat (surface temperature of 24 ga pipe is roughly 1/2 of the flue gas temperature).
While I have these certain concerns as a professional I am certainly not suggesting that one not go with a rocket mass heater. It is only a matter of time until there are accurate standards and codes for them. As an innovator and scientist I am quite enthusiastic about this technology. I am actually planning to build one in a cabin in the coming months.
John, thanks for the very helpful post.
I'll get a copy of NFPA 211 and i'm sure it will help me to get either my RMH or my masonry heater approved. Seems like the NFPA guidelines are scattered all around the internet as bits a pieces, unless you pay $43 for a pdf. Ill figure out how to score a copy.
Good point about the wood stove combustible clearance guideline. Good things to take into consideration.