Digital vs old type thermostat - DIY Home Improvement, Remodeling ...

With my furnace problems and my oversize (168,000 input BTU/hr, 80% efficient) furnace being on only 1/3 of the time in winter, today I measured a cycle, once the setpoint had been reached.
It was the blower being four minutes on and 6 minutes off, a 40% duty cycle.

I have never been able to get a definition of short cycling but this sounds like an example of it.
Four minutes on is probably too short in any case but once the setpoint is reached I'd think a low duty cycle is expected.

Anybody have a short cycling definition for house HVAC, what it is and what it is not? It should probably involve both on-time and duty cycle. Maybe you'd also need a per hour basis to take into account the heat capacity of the house?

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Last edited by Wuzzat?; Yesterday at 05:39 PM.

Source: http://www.houserepairtalk.com/f8/digital-vs-old-type-thermostat-15488/

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