I have a dual fual heat pump and gas furnace. The heat pump is a 2 stage unit and the furnace is a 2 stage unit as well. Am I correct in thinking I need a 4 heat and 2 cool stage thermostat. Such as a Honeywell prestige iaq
What is now running these two units? What makes the gas furnace two stage? Do both systems run together or heat/cool two different parts of the home or business? The Prestiage works with RedLINK products by Honeywell. It’s installation manual is quite good and explains how to add relay switches to control multiple systems.
It will allow through a relay blocks to turn on one or more heating or cooling systems. When a second stage is required it will turn on both systems second stage through relay blocks.
There is not a thermostat that can run two system and walk through each of the four stages independently if that is what you’re looking for. Reading briefly through the specs it can only handle three conventional heating stages, not four.
I thought with dual-fuel the gas burner & heat pump were never running at the same time, since the incoming air from the heat pump coil into the gas burner's heat exchanger would be too high(?). The higher incoming air temp leads to lower heat exchange efficiency on the gas burner (especially if condensing) and going overtemp on the heat exchanger. This isn't a problem for resistance auxiliary heat strips (which can operate safely and at the same efficiency at any incoming air temperature and can easily be modulated), but a complicated control issue for combustion equipment.
Many 2- stage gas furnaces use a simple (sometimes programmable, sometimes not) timer to determine when to kick up to the high stage, with no direct thermostat control of the second stage.
Without so much as a model number it's impossible to take more than a WAG at the control scheme and thermostat compatibility. It's sort of like asking "What type of fuel injection controls do I need for my hybrid car?".
You have communicating units so should be able to use Goodman's communicating thermostat. What does the installer recommend?
This is awkward, but...
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