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What's a good duty cycle?

mxfrank Member Posts: 22
We've had record cold temps in the Hudson Valley, so it was a good weekend to measure the performance of my boiler. Background: It's a Buderus G205 oil-fired boiler, Riello Burner, 1.25B Nozzle @ 145 psi. Serves three baseboard zones, two forced air zones and a Buderus DHW tank (the house was built over many years as a series of additions). Over 24 hours yesterday, when record low temps barely rose out of the single digits, the duty cycle was 52%. To me, that means the installation is 100% oversized. I'm wondering what all of you think an ideal duty cycle would look like. 70%? 80%? 100? Or am I good?


  • mxfrank
    mxfrank Member Posts: 22
    I should have mentioned that I locked the thermostats at 65, no setback. So the duty cycle would be a bit higher at 70 degrees.

    I think it's pretty tough to achieve 100%, especially with an old house with varying construction standards. Reasons why may be that there's fudge in the calculation, sometimes intentional, sometimes wrapped into the textbook heat loss factors. The story with this house is that at some point, two heating systems and a DHW tank were combined into one system. The firing rates of the various burners were added up, and there ya go. I'm actually relieved that it's only 100% oversized...I was expecting much worse.

    So here's the question. If the duty cycle is presently 50-60%, would it be worthwhile to downsize?