|Before you replace that burned out furnace or boiler with a new one, make sure it is the right size to begin with. Don’t take for granted that the original installer didn’t make a mistake. Especially where forced air furnaces are involved, the sizing of the ductwork is critical to the heating capacity of the entire system.
A 150,000 btu furnace feeding ductwork sized for 1000 cfm does not deliver 150,000 btu to the dwelling. Most likely, the burner kicks out on high limit due to over heating. Which is what it should do if there is not enough air flow. In such a case, this furnace has never produced at full capacity, and it’s longevity was shortened by the steady over heated condition.
All furnace manufacturers match btu and cfm output; if the ductwork cannot support the cfm requirement, the furnace will not perform to it’s potential. When replacing a burned out furnace, match the btu to the ductwork as best you can.