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MHA Proposed OTFDC Definition of a Masonry Heater 

Definition

A masonry heater is a heating system of predominantly masonry construction having a mass of at least 800 kg (1760 lbs.), excluding the chimney and foundation, which is designed to absorb a substantial portion of the heat energy from a rapidly-burned charge of solid fuel by:

a) routing of exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes at least one 180 degree change in flow direction, usually downward, before entering the chimney, and 

b) being constructed of sufficient mass such that under normal operating conditions the external surface of the heater, except in the region immediately surrounding the fuel loading door(s), does not exceed 100°C (230°F). 

Note: Three characteristics distinguish the masonry heater from the mainly decorative masonry fireplace: first, it is designed to be operated with its tight-fitting loading door(s) closed; second, it is intended to function as the primary or a significant supplementary heating system for a house; and third, the chimney serving the heater is not usually supported by the body of the heater, but rather is located behind or beside the masonry heater where it may share a common wall with the heater facing. 

Rationale:

This definition is provided on the assumption that some users of the code may not be familiar with the characteristics of masonry heaters and so that the code user has context for the provisions referring to masonry heaters.