Need thermostat advice


Old 05-02-17, 10:20 PM
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Need thermostat advice

I am choosing a thermostat configuration for my split system all electric. I have a 4 ton compressor. The air handler has two sets of 10 kw strips that can be activated in two stages when the mercury drops. Mostly I am concerned about energy savings. There are several wiring configuration options. The preferred seems to be 2 outdoor t-stats for low temp cutover plus an EHR. Is this the best option? Or would I be better off forgetting the outdoor stats and upgrading my indoor control to a smart unit (nest, ecobee, lyric) that has heat pump/aux balance controls? My current indoor t-stat is a Honeywell programmable (rth7600d).
Old 05-02-17, 11:21 PM
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Welcome to the forums.

Your location is important in this discussion.

For maximum energy savings you want the heat pump to do as much of the heating as possible. That means it should be allowed to run without any setback.

An outside sensor/thermostat can be set up to shut the heat pump down if the temperature is too low and it can no longer perform. Heat pumps can run long into low temps.

A heat pump system needs to defrost during operation. While defrosting... the electric coils are activated to keep warm air blowing.
Old 05-03-17, 05:13 PM
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Thanks for the reply. So I've convinced myself I don't need the outdoor cutoff thermostats if I purchase an Ecobee3 or Nest. Which both claim to be able to control a single stage heat pump plus 2 stages of auxiliary heat depending on the weather.

On the Ecobee website they describe the following configuration:

But i'm confused... wouldn't this wiring activate both the heat pump and 1st stage auxiliary at the same time?

They describe the system setup in this wiring configuration here under "Accessory Relays":

I want the heat pump to activate independently of the heat strips, which I would want to activate only 10kw or full 20kw as needed (when very cold outside). The airhandler allows this, I just need to find a thermostat that will sequence this correctly.
Old 05-03-17, 09:00 PM
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The diagram that you posted has only one terminal for the electric heat strips.

I would use the Honeywell Prestige IAQ and a wireless outdoor temperature sensor for that application. It would allow for staging of the heat strips and allow you to lockout the heat strips above the outdoor temperature that you set.

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