Woodstove to RMH Conversion - My Planning and Execution Thread

The heating season is behind us, and after one winter in this house burning gobs of wood in a Blaze King, I would like to work towards a RMH to do the heating. The house is large, the Blaze King is the biggest one on the market, and the former owners have some clever natural convection and forced convection features to allow one stove on the ground level to reasonably heat the house. However, I look at all the soot in the chimney (which was cleaned before we moved in last October, right at the start of heating season), and I know we are throwing away a lot of energy up the flue. So, this is the beginning of my RMH journey. I have done masonry work, I have worked a bit around refractories in a foundry, but this will be a learning experience!

The basics - The usable area for the RMH is tucked in a corner, and thus limited in size. It will need to fit in a plan area of 4 x 6 ft, with the chimney aperture about 7ft up the wall, where it transits to the garage and goes vertical for about a 25ft rise to clear the roof.  It's a rather long chimney, as it's a rather tall house. The chimney is double-wall stainless, 8in inner diameter, 10in outer diameter. This will be the chimney for the RMH, as it's the only game in town, and I don't want to change it for laziness and permit-y reasons. Pieter van den Berg of Batchrocket.eu suggests that the riser diameter must be <= chimney, so I can do up to an 8in riser. I expect I may need to lay a fire-rated wallboard layer over the interior drywall here, and I will give some thought and analysis to how close the bell wall should be to the house wall - comments welcome on this if anyone has good data.

My intent is to experiment with one or two bare cores outside, to practice the build, and then build the real one (so it is not my first build - I would like it to last). The Blaze King heated this house for ~17yrs, and is beginning to show its age, as there are a few places where light can find a way through the walls now, though all are in suction areas, thankfully, and the CO2 and CO monitors have never indicated any buildup of either gas. So I have until the next heating season to figure this out, which should, if I hustle, be enough time.

I will keep this thread updated from time to time with progress, and perhaps some of you will be so kind as to critique or comment if I say or do something known by rocket scientists to be a bad idea! I was very much inspired by Glenn's awesome work here, so thank you to all who have contributed RMH wisdom!

Happy home heating,
Mark

How exciting, Mark!
It sounds like you are ready to go.

Are you thinking of a single or a double skin bell?
A 6" batch will fit your build plan much better than the larger 8".
Although your home is large, once you get a bell up to operating temperatures, your home will be amazingly warm.
You can always load a 6" twice to match the 8" in performance.

Take a look at the ISA numbers for a 6" & 8"
The box is bigger on the 8", so it would burn longer, but the corresponding Bell size is larger.
A 6" batch is plenty big, especially as Peter approved up to a 25% increase in the box length.
As I mentioned, you can load a second load of wood if you feel you need more.

It is a radical life change to switch from heating a steel box (and the great outdoors) to heating with bricks.
You will be blown away!

Once you go brick, you will never go back!

Code for masonry heaters (with the code-required double skin) is a minimum 4" gap to combustible walls. For an exterior wall, you would want that gap to allow heat circulation into the space rather than only to the exterior wall.