Not switching to alternate fuel when time to heat is long.

[Patrick43]

I have a dual fuel heat pump with propane gas furnace as back-up.
The heat pump lockout is currently set at 40F. The current outdoor temp. Is 46F.

The heat pump does not seem to be able to keep up with the demand of 70F. The air temp out of the registers does not seem very warm. When the thermostat temp is increased by even an outrageous 8 degrees or more the thermostat will say 2+ hours instead of just transitioning to the alternate fuel-Gas Furnace. 

Is it possible some of the wiring or settings could be off? I have the Alt Heat wire to W1 and power to Rc. Nothing in W2 or *. 

[laurentbourg]

I do not think the Nest has algorithms to switch to the less efficient fuel system when time to heat is high when using a lockout temp, it is exclusively driven by that lockout temp. Outdoor 46>40 and therefore time to heat is based on the heat pump. If you want a smarter heat pump strategy, you need to set the heat pump balance settings in the Nest sense menu on the device, but unfortunately I don’t think those settings are available for dual fuel. 

[Patrick43]

 

Correct, there is no option to change the heat pump balance.
So rather than switch to gas, the nest will run the heat pump for 6+ hours because it can’t raise the temp 2 degrees? My old $30 thermostat seems to preform much better. My heat pump is running non-stop and is struggling to reach a 2 degree increase.
I can run a test of Alt. Fuel, the furnace kicks on, and hits the 2 degree increase in a few minutes. 

[laurentbourg]

Ok thanks. You could try to use W2/Aux instead of W1, configuring that connection as dual fuel and then determining whether the heat pump balance settings become accessible. I have not tried this setup so I am not sure it will resolve the issue but worth a try. 

[laurentbourg]

On a separate thread, I am not sure why your heat pump is so inefficient running with an outdoor of 46F, that should not be the case, those things work well all the way to 30F, you might want to have an HVAC professional service it.