We are considering installing a tankless propane on-demand water heater in a residential setting, where multiple tenants use a shared bathing facility (presently served satisfactorily by a 40 gal electric tank heater). A big concern about installing a propane tankless heater, is the possibility of a cold air down draft in the chimney into the unit and having the core freeze (and break). We experience wintertime lows outside temps of -40°F to -50°F and colder.
In this setting there might be early AM use and then, possibly, a long period through the day with no demand until dinner time. (i.e. natural use will not necessarily have the unit cycling on and off).
Does anyone know of units where there are dampers in the flue that positively (as opposed to passively) close that would protect against such a freeze up. Anyone with direct experience?