[buffalobillpatrick]

Dend, your:
“It's true regardless. A 50% duty cycle at design conditions is Short Cycling.”

U R confusing a boiler that is oversized for the home heating load at “design” temperature
(2*F) here, with Short Cycling.

It’s not oversized for my house DHW load when 2 showers are on or filling a large bathtub.


Hot Rod Rohr (HR) who is Caleffi’s USA technical communications lead defines “Short Cycle” as:

“More than 3 boiler cycles per hour or boiler cycles less than 10 minutes in length.”

“If you look at it from simply a cycle life of the components, regardless of efficiency, that 10 minute on/ off is the guideline I have used.”


My boiler firing time will be: 30 minutes minimum in Summer, and much longer in Winter.

BTW, my boiler don’t waste heat at the end of a cycle, it burns clean until the moment that the gas valve is closed and then the residual boiler heat from the cast iron is pulled out & used by an adjustable post purge cycle of the boiler pump.

ModCons never again!