Need a T-stat that work in 1 degree difference


Old 01-01-15, 07:55 AM
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Need a T-stat that work in 1 degree difference

Happy New Year all!

Ok, I've searched all over so here I am.

I have a new construction home, Rhuud heat pump with 5 KW heat strip installed.

My issue is, I have a Honeywell TH8000 that will only turn on heat strips if there is a 2 degree difference, meaning I have to crank it up to 74 to get it to turn on. And then when it does, wont turn off until 75, to hot.

Right now, the HP can only get to 72 on a cold day by itself. It cant break 72 without the strips.

Does anyone make a T Stat that will kick on auxiliary heat with 1 degree? or turn on Aux if it struggles? mine just cycles over and over at 72 trying. I I do not have an outside temp sensor hooked up, is there a T-stat that could use an outside temp sensor to say "Hey its too cold, turn on aux heat. My installer sucks and he is in over his head.
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Old 01-01-15, 08:24 AM
firedawgsatx's Avatar
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You might try changing function 680 to 3 as shown on page 9 of the installation manual for your thermostat:

Your thermostat has the capability to use a remote sensor to lockout the heat pump and use only auxiliary heat as explained on page 11. Your thermostat should energize the auxiliary heat when the heat pump can't keep up with heating the house by itself. It should also energize auxiliary heat when the heat pump goes into defrost mode.

Also check function 600 to make sure it is not set at 72. Many times a home builder will set the thermostat so that contractors can't adjust the heat above a certain temperature while they are working in new home construction.
Old 01-01-15, 08:29 AM
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There are plenty of options on that stat,are you sure it is configured correctly for your system?
Old 01-01-15, 08:51 AM
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I have a Robertshaw 4320 (3Heat,2Cool) that I like because it gives me quite a bit of control over the 2nd and 3rd stage heaters and could deal with your complaints (which used to be mine too).
And it was moderately priced, around $60 a couple years ago as I recall ...

For example, in cold weather, I set the thermostat to bring on 5kw after 5 minutes of compressor or immediately if the temperature difference is 2 degrees below 1st stage set point . And then bring on the 3rd stage (another 10kw) after 20 minutes or 2 degrees.

The thing I like is that once the auxiliary heaters kick in, the thermostat keeps them on for the duration of the cycle so that it doesn't cycle on and off as the set point gets close.
And the temperature difference (I think down to 0.5 degrees) and timing options (5 to 40 minutes) are pretty easy to change when the weather dictates.

When last I looked, had all of their manuals on line, making it possible to figure out how the thermostat will suit your situation, and the one time I 'phoned tech support they were actually reachable and helpful.

I bought mine a few years ago at, now supplyhouse I think.

Most of the recommendations I see here are for Honeywell, but when I checked them out they seemed to offer a lot less ability to control to ones situation.
Old 01-01-15, 09:25 AM
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Great! Ill check that one, out, thank you.,
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