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house92 02-01-2013 07:18 AM

Digital vs old type thermostat
I have the older type thermostat with mercury and the heat anticipator. I was considering replacing my current thermostat with a digital one, but a friend said he thought the digital ones ran all the time due to keeping the temp within 1 degree. He said his unit runs a lot more than when he had his older thermostat, and he doesn't like that. What do you guys here recommend?

Wuzzat? 02-01-2013 08:03 AM

The energy used to heat your house will be the same with the old or the new t'stats and the comfort level should be better with the new because the temp is more consistently maintained.
Short cycling of his new t'stat may have other causes than going to digital.

Austin 02-01-2013 08:53 AM

I have an electric and have noticed no differences in my heating/cooling cost.

kok328 02-01-2013 03:58 PM

If you purchase a digital stat, get one with a programmable offset/differential. This will prevent short cycling but, may prove to be a little uncomfortable with the wider swings of indoor temps.

Wuzzat? 02-01-2013 04:31 PM

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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