Masonry Heater Level Two

Codes, Clearances, and Anatomy

If you haven't seen my basic Masonry Heaters video, I hope you'll check that out before digging into this. click HERE.

Clearances are such that a heater can be seamlessly integrated into a home plan, whether it's out in the open, in a corner, or against a wall. Heaters can even function as walls themselves, and do an amazing job of connecting adjacent spaces while defining them as independent areas.

Codes, Clearances, Supports, and Venting

Let's start at the bottom and work our way up. Masonry Heater codes most often reference ASTM E-1602. I don't believe I can share the document in it's totality here, but if you want to buy a copy you can do so here, or call me for more info (link here). ASTM E-1602 specifies clearances based on wall-thickness while allowing for laboratory testing for non-conforming wall assemblies. Testing every heater we sell is prhibitively expensive, so we follow ASTM E-1602 for wall thickness and so on.

Here's what it means for you:

1- Support.

Supports requirements are the same as for conventional wood-burning fireplaces. This makes it easy as Concrete Contractors and Masons already know what to do. We just hand them a footprint and any needed consulting. Clearances are also the same on supports, namely 2" to combustibles.

This means that when we get to our stove, we're most often starting with a concrete slab just below finish floor level, although we can build the stove on a pedestal as well, which is traditional in Germany and gives the floor of the the heater as a radiant surface as well.

2- Heater-Wall Clearances

The walls will be a minimum of 4" from combustible framing, but "wing walls" are allowed which often create the illusion that the heater is built up against a wall. This gives a clean look.

3 - Heater Door Clearances.

A non-combustible floor is needed, extending 20" in front of the loading door and 12" to each side of the loading door. There is also a requirement that requires a heat shield agains a combustible wall when the loading door is perpindicular to an adjactent wall (in a corner), but I've never built a stove is such a situation. It would be aesthetically awkward and in most cases we would ust a corner design with the firebox at a 45 degree angle.

4 - Clearance to ceiling

8" clearance is required to celing, but like the walls, as long as the space above the heater is vented to block static heat build-up, a heater can look like it extends to the cieling.

5 - Venting (Chimneys)

Some heaters are designed to connect with a chimney next to or behind the heater at the base (floor height) while others attach higher up and some exit from the top of the heater. This last is the most common method we use, and the most common chimney in this use is a 6" (inside) Class-A double-walled and insulated stainless steel chimney. Most often we use base exiting heaters when there's a masonry chimney involved, whether it's there because there's multiple flues or it's already built, or in some cases for aesthetic preference. Both Class-A and Lined Masonry chimneys require a 2" clearance to combustibles.