Mizer

Therm_lag

Condensing boilers and furnaces do a good job extracting heat from combustion gases.  For steam boilers, what is the potential efficiency improvement using stack heat recovery?  From the excellent review at Energy Solutions Center (dot ORG), savings potential is based on the existing stack temperature, the volume of make-up water needed, and the hours of operation.  Economizer would be more effective when it could pre-heat domestic water, and where boiler has been downsized or derated (see "Zoning 1-pipe," "Is EDR everything?" and threads on derating) thereby extending hours of operation.   I can see a steam boiler using stack economizer functioning as a combined heating appliance - a nice proposition in multi-unit residences where DHW is a greater percentage of gas use.   Let me know if there is already a well-developed thread on economizers - I searched several times.