combining a gas heater and heat pump

[thammel]

I just got a Reznor udas separated combustion heater for my garage. I want to buy a mini split heat pump and would like to set up the control system (thermostat) so the heat pump runs when the outside temp is about 35F or above and the Reznor kicks in below that. Anybody have any ideas how? Are there available t-stats that do this? I could always get one of my smart EE buddies to rig up a custom control system but I'd rather take the easy approach first, if there is one.

Thanks!
Tom

 

[Hlidskjalf]

Basically what you need is a two stage thermostat. The thermostat will not work exactly as you described. Newer thermostats are more sophisticated in staging these days. Program your gas heat as first stage, and your heat pump as the second. Depending on the demand, the thermostat will call one one or both heating stages.

I'm sure if you are really set on having your system operate as you described it can be done. It will just end up being a lot more work in comparison to a two stage thermostat.

 

[trythis]

My geothermal system uses a gas backup, but only operates when the inside temp is below required level for 5 or 10 minutes after the geothermal system has been running.

The dual stage thermostat Hlidskjalf mentioned would do it for you, except they dont usually operate based on outside temps. I am sure they exist, but you will have to look for someone that has knowledge of them.