Although the market for gas-fired boilers continues to track toward those that can modulate and operate with sustained flue gas condensation, conventional boilers (e.g., those not designed to operate with sustained flue gas condensation) still represent a significant portion of the market. All oil-fired boilers fall into this category, as do copper tube boilers. 

Some of these conventional boilers will be for higher temperature heat distribution systems, such as those using fin-tube baseboard or air handlers with minimally-sized coils. Some will also go into lower temperature systems serving radiant panels. The latter will require a mixing assembly between the boiler and low temperature heat emitters.