Spacing between fire brick and facing bricks

Our Masonry heater is backed up to a wall, we are just using bricks back there as the facing between the firebrick and the wall, as it will not be seen. We have the 4" spacing from the wall, our question is how much spacing do you recommend between the firebrick and the facing bricks if any? We want to build it up as we go up with the fire brick.

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@dclaire, thanks so much for airing your questions on the forum and welcome! It would be really fun to see pictures of your build as you go.

Regarding the space, it would be good to read this article on expansion joints for masonry heaters. Because your core is 8” off of the wall, you can lay the whole core up, install an expansion joint and then lay the whole facing. As you say, the brick work on the back does not need to be pretty.

This is how we do it. There are many ways to do it and there are some Eastern European traditions that don’t use expansion joints at all. It is one of the trickiest things about the heater building trade… dealing with the expansion of materials as they heat up.

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Great article, thank you. We could use more information about incorporating the facing with the doors of the fire box, and oven and also the clean out openings. Are the doors attached to the fire brick or the facing?

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A post was split to a new topic: Masonry Heater Hardware Installation Instructions

Great question @dclaire. I split my reply into a new post linked above.

The space between the veneer and fire chamber were required by code standards I had read. Didn’t need them where my two furnaces were built but I used them none the less. I built the heat chamber first. Then the veneer layout. I used oiled plywood to maintain space as the veneer went up. Primitive but functional. Wasn’t able to upload my images so here are links to them from my site.

In reading the article you have referred to, I am wondering what do you mean when you state: Once I have built my masonry up past the core, I line that with 1/4″ ceramic paper and then fill with my insulative mix of perlite and clay/lime/cement.?

@dclaire, this is the location of the 1/4” ceramic paper I am talking about:

With a soft enough insulation (ceramic wool, clay or lime + perlite), this may not be necessary. The idea is to be able to allow the core to expand and contract like a piston inside of the facing and not bond between the core and facing, even at this insulation layer. It has been observed that the greatest expansion in the core is vertical (since is often the largest dimension). All this said, I’m not sure if this detail is necessary.