OmniStat 2 - Heat Pump vs Dual Fuel Heat Pump setting

[mikeindustries]

Hi there. I've been using an Omnistat 2 for about 5 years now to control a Rheem Electric Heat Pump with a gas furnace backup. I have noticed that the gas furnace never turns on unless I manually turn the mode to "EM Heat".
 
I thought, for some reason, when this system was installed that the purpose was to switch over to the gas furnace when the temperature gets so low outside (under 35) that it's more efficient/fast to heat with gas than with electricity.
 
In reading the Omnistat installation manual, it seems like there are two ways to set a system like mine up: heat pump and dual fuel heat pump. If I'm reading correctly, "heat pump" (with 2-stage heat) does exactly what my system is doing right now: sticking to electric unless there is an actual emergency or the system physically can't keep up. "Dual fuel heat pump" seems to be designed to do exactly what I *think* I want to do: use electric as the primary until the outside temperature drops below 35 and then switch to gas as primary.
 
So, three questions:
 
1. Am I describing the two modes correctly above?
 
2. With my setup, do I indeed want "dual fuel heat pump"?
 
3. If the answer to #2 is yes, is the only change necessary simply switching this setting? I am hoping no rewiring is required since I can successfully trigger the gas furnace by engaging the EM Heat setting. Also, I think my outside temperature sensor is connected to my HAI board and not the Omnistat directly. I'm assuming this isn't a problem since I do get an accurate "outside temperature" reading on the Omnistat display itself.

 

[ano]

Also, I think my outside temperature sensor is connected to my HAI board and not the Omnistat directly. I'm assuming this isn't a problem since I do get an accurate "outside temperature" reading on the Omnistat display itself.

I read the instructions to say an outdoor temp sensor MUST be connected to the Omnistat 2 for dual fuel. It doesn't say this is an option if other outside  temp. is supplied.

 

[mikeybob]

I have a similar setup with a heat pump and gas furnace backup.  I’m using the “dual fuel heat pump” type with “auto changeover” mode, and the system is working as you described…switching over to the gas furnace with the temperature drops below 35. 
 
My guess is that you could switch the setting and get the behavior you’re after…but I’m not 100% sure.
 
I’m using the same setup as you for the outside temperature sensor, it’s connected to the HAI board not the Omnistat.

 

[ano]

I have a similar setup with a heat pump and gas furnace backup.  I’m using the “dual fuel heat pump” type with “auto changeover” mode, and the system is working as you described…switching over to the gas furnace with the temperature drops below 35. 
 
My guess is that you could switch the setting and get the behavior you’re after…but I’m not 100% sure.
 
I’m using the same setup as you for the outside temperature sensor, it’s connected to the HAI board not the Omnistat.

I read it again, and I see that now. If its NOT receiving any temp sensor it says the display flashed red, so if it isn't it must be happy.

 

[mikeindustries]

Thanks mikeybob. I will switch over the mode setting and give it a shot!