CODE info ~ Ernie & Erica on the Permies Forum

Erica Wisner post on the above link:

There was a little about this in an earlier thread:


There is an ASTM standard for masonry heaters: 1602-03, and it is possible to build a rocket mass heater to meet existing masonry heater standards, clearances, and footing/earthquake standards. It involves a lot more firebrick; you set the ‘lining’ (instead of ducting) in ‘fireclay mortar’ (instead of cob), and include ‘expansion joints’ which as far as I know, can be a piece of cardboard form that you leave in place after using it to shape your fireclay-stabilized perlite insulation. You might have to go to a conventional masonry casing (with, ugh, cement type mortar) outside of that expansion joint, or maybe they would accept ‘monolithic adobe, with integrated fiber reinforcement’ as an internationally-known building material that is fireproof and offers healthful benefits by mitigating some air quality concerns.

I would go to woodstove clearances around the barrel. And you may need refractory insulation and a custom barrel/bell to scale up to a public-building size.

If you have a willing engineer (God bless you, NY!) and an alternative-approvals process where they know about masonry heaters already, you have a lot more in your favor. It will still be a roughly $5000 solution, at a guess, not a $50 solution, to do this up to spec for a public building. That’s not counting the permits or engineer’s time.


You might also look into the already-UL-approved masonry heater kits that are sold from Canada and the eastern USA. The core can cost under $5000, and then you would be looking at additional casing work but saving a ton of permitting hassles (because it comes with a sticker, or certification document).


They still might be leery about solid-fuel devices, somebody has to read the owner’s manual and operate the thing, and they are seriously and rightly paranoid about fire in public buildings.


We have had several public schools shut down in Western Oregon in the last decade or so due to major, toxic mold problems. Pre-1950’s buildings are hard to heat due to more use of masonry and windows, less insulation; a thermal-mass heater could be useful in this situation, if the building will be continuously used throughout the week.

Post-1960 buildings are hard to ventilate because of over-confidence in the miracles of better living through chemistry (concrete, windowless buildings).

If mold and indoor air quality are the HVAC concern, not just heat, then you have a larger problem. Creating decent ventilation in a poorly-designed building is a cat-in-the-hat, and it would take a careful on-site investigation to determine if there is a low-cost passive-solar solution, or if it’s a case of the building is unavoidably unhealthy unless you run fans throughout occupied hours.


There’s about 4 1/2 cents worth.