Brick RMH Bell On Interior Wall

[foxtatic]

I have a corner of the dining room where I would like to put a mass heater, but due to a doorway, I don’t have room to build it out away from the wall. I have seen many other builds up against walls. Mine will be a 6” riserless core in an appropriate sized brick bell. My walls are circa 1950 cement board with a thin layer of plaster from a time between the old “lath and plaster” and the invention of gypsum drywall. I found this out the hard way when I knocked out another wall!



The nature of this cement board means it could absorb heat since it has some mass. But still, it’s painted and it may not be ideal to build the brick bell touching it. What would you do in this situation? Insulate the wall, build up against it, leave a 1” gap, or find somewhere else entirely to build? The only other heater I have built was metal-walled so I have no concept for how hot a brick bell actually gets.

[josephcrawley]

Heat shielding with a gap can block an impressive amount of heat. Built a sauna with a Vogelzang stove and due to space constraints needed it as close to the wooden wall as possible. Used three layers of sheet steel each with a one inch air gap. The wall wasn't even warm behind the third layer. With the external temperatures of a mass heater I think you would be fine with two. Definitely put a fan back there to exhaust heat buildup and to improve efficiency.

[peterberg]

We live in a wood frame and plasterboard house. The mass heater is close (about 4" to an inside wall which got quite hot, too hot for my liking. I mounted a corrugated steel sheet behind it, just 1/4" from the wall. It really works wonders, when the heater's rear wall is too hot to touch the heat shield is just handwarm, nothing more.

Later I did the same with the DSR3 prototype which was placed about 3" from the wall. This heater, not being a mass heater, got much hotter. Same effect: the heat shield just over handwarm while the heater was scalding hot. Remember: such a heat shield shouldn't be resting on the floor but about 4" higher at least.
Here's the one behind the DSR3, which is pulled away from the wall in order to make room for the chimney sweep.

[foxtatic]

Indeed the sheet metal with air gap does work great and I'm using it behind my 7" DSR2 shop heater since it's an all-metal exterior.

But I notice that some mass heater builds (like the 200mm DSR3 you went to have a look at, Peter) are built right up against the wall. In that case, they are a strawbale house. How do they get away with having that huge mass heater touching the wall?

[peterberg]

There's an air gap from the other side, with a reflector against the wall. The gap is closed at the left hand side, just for esthetics.

[Forsythe]

Oct 10, 2022 12:28:57 GMT -8 peterberg said:

There's an air gap from the other side, with a reflector against the wall. The gap is closed at the left hand side, just for esthetics.

In the ASTM code (E1602-03) for North American masonry heaters, (pg 6) they call that a "wing wall"

3.2.20 wing wall—a noncombustible lateral projection from the exterior wall of a masonry heater for use in bridging the space between a masonry heater and a combustible partition wall.

There's a copy of the whole masonry heater standard *currently* available here:

pdfstandards.net/?smd_process_download=1&download_id=3967

(ASTM standards are usually copyrighted documents that have to be individually purchased — so I don't know whether this copy is "officially sanctioned" or not... but IMHO it should be against the law for a local government to make a part [or more often MANY parts] of its building code copyrighted material ...meaning that you have to pay money to a private entity — ASTM just to find out what the local law even is in order to not break that law by building something against each individual section of code. ...Each cited ASTM code costs around $45 dollars just to access, and building codes often cite ASTM standards by the dozens... Having to purchase the law from a private entity in order to follow said law — is the very definition of nepotism and graft and it should be criminal...especially when something like covid lockdowns made it impossible to access your local gov't office's own copy, in person... But I guess that's a vehement rant I have on a different topic...)