[osubuckeye88]

Hi everyone:
I have an electric heat pump heating /AC system with fuel oil ( home heating oil) backup.
So when the temps get low enough, it kicks on the fuel oil ( auxiliary)

My thermostat seems to be malfunctioning. Do I need a special thermostat replacement with "auxiliary" ? Or will any basic Honeywell thermostat work ?


My current model is
Honeywell Home RTH7500D1049/E1 rt drz
but it costs over $100 more than a standard thermostat.

Thank you!

Honeywell Home RTH7500D1049/E1 rt drz, Large, White - Programmable Household Thermostats - Amazon.com

Honeywell Home RTH7500D1049/E1 rt drz, Large, White - Programmable Household Thermostats - Amazon.com

www.amazon.com

 

[CaptTom]

I think the "Auxiliary heat" function is pretty common. Assuming that works using the old one, any thermostat with that feature should work. Would need to know more about how it's currently wired to be sure.

Also, if you're buying a new thermostat anyway, I'd look for one with WiFi access capabilities. Honeywell has a bunch of these, which look very much like the one you linked, which doesn't seem to have that feature. It's really handy to be able to monitor and control the HVAC system when away from home.

 

[sktn77a]

Any thermostat that is "heatpump-compatible" should work. You might want to consider a thermostat with a larger display.

 

[57TinkerMan]

Go with the Ecobee 3 Lite. Supports duel fuel, easy to install. Check your utility company they might have special deals on thermostats. Not all heat pump compatible thermostats are duel fuel capable.

https://www.supplyhouse.com/Ecobee-EB-STATE3LT-02-Ecobee3-Lite-Thermostat

 

[57TinkerMan]

I should add that you need an internet connection for the Ecobee 3 to get weather data for the changeover temperature.

 

[osubuckeye88]

Further info: I do not want an internet connected device. I dont use smart home devices . I am just searching for the least expensive, decent thermostat which will handle the auxiliary heat system. Thanks everyone

 

[57TinkerMan]

Your oil furnace cannot run at the same time as the heat pump. You need a duel fuel capable thermostat with an outdoor temp sensor. Image from the T6 installation manual, this one is not wifi. Sensor is ordered separately.

https://www.supplyhouse.com/Honeywell-Home-TH6220U2000-T6-Pro-Programmable-Thermostat-2H-1C-Heat-Pump-2H-2C-Conventional

 

[57TinkerMan]

Less expensive.

https://www.supplyhouse.com/Honeywell-Home-TH6210U2001-T6-Pro-Programmable-Thermostat-2H-1C-Heat-Pump-1H-1C-Conventional

https://www.supplyhouse.com/White-Rodgers-1F85U-22PR-5-Display-Universal-7-Day-Programmable-Thermostat-2-Heat-2-Cool

 

[user_12345a]

There are three ways to do a dual fuel system and only one requires a dual-fuel capable thermostat.

1. The most primitive -> connecting furnace heat signal to Emergency heat terminal on thermostat and manually changing over
2. Regular thermostat with a fossil fuel kit that uses outdoor thermostat
3. Dual fuel capable thermostat - ideally using a outdoor temperature sensor.

Your current thermostat is not dual fuel capable - if it is automatic you must have a fossil fuel kit.

The current setup including wiring, any fossil fuel kit needs to be evaluated before buying anything.

What is the thermostat doing that makes u think it's malfunctioning?

 

[osubuckeye88]

Your oil furnace cannot run at the same time as the heat pump. You need a duel fuel capable thermostat with an outdoor temp sensor. Image from the T6 installation manual, this one is not wifi. Sensor is ordered separately.

[/QUOTE]
Thank you for clarifying that.

 

[user_12345a]

Switching to a dual fuel thermostat rather than fossil fuel kit if that's what u have would require significant re-wiring and configuration.

Fossil fuel kits are kind of obsolete but still available.

 

[osubuckeye88]

Switching to a dual fuel thermostat rather than fossil fuel kit if that's what u have would require significant re-wiring and configuration.

Fossil fuel kits are kind of obsolete but still available.

Way over my head

 

[user_12345a]

Way over my head

To put it simply, you need to see how your existing thermostat is wired and where those wired go. Which wires are connected to which thermostat terminal and what's on the other end.

There may be a box with a control board wired in between the thermostat and heatpump + furnace that changes over to oil below x outdoor temperature.

This is necessary to guide you when it comes to which thermostat to buy and how to set it up.

...because your existing thermostat model does not natively support dual fuel, i am betting you have the box or oil furnace is wired to E terminal on existing thermostat for manual-change over which many new thermostat do not have.