MHA Masonry Heater Definition

A masonry heater is a site-built or site-assembled, solid-fueled heating device constructed mainly of masonry materials in which the heat from intermittent fires burned rapidly in its firebox is stored in its massive structure for slow release to the building. It has an interior construction consisting of a firebox and heat exchange channels built from refractory components.

Specifically, a masonry heater has the following characteristics:

- a mass of at least 800 kg. (1760 lbs.),

- tight fitting doors that are closed during the burn cycle,

- an overall average wall thickness not exceeding 250 mm (10 in.),

- under normal operating conditions, the external surface of the masonry heater, except immediately surrounding the fuel loading door(s), does not exceed 110 C. (230 F.),

- the gas path through the internal heat exchange channels downstream of the firebox includes at least one 180 degree change in flow direction, usually downward, before entering the chimney,

- the length of the shortest single path from the firebox exit to the chimney entrance is at least twice the largest firebox dimension,

(passed unanimously at 1998 MHA Annual Meeting, June 8, 1998)