AC and Boiler Heat

Other Devices & Integrations Climate Control & Temperature Sensors
1

I have a gas hot water boiler and radiator system for heat. Then a unit in the attic for AC. Currently they each have their own thermostat.

The AC unit is a standard 24V system, as explained by my AC guy. I’m not sure what the boiler is. Can I use a Trane or Honeywell z-wave compatible thermostat? Can the 24V from the AC also feed the boiler when the heat is on?

2

[quote=“wkm001, post:1, topic:175739”]I have a gas hot water boiler and radiator system for heat. Then a unit in the attic for AC. Currently they each have their own thermostat.

The AC unit is a standard 24V system, as explained by my AC guy. I’m not sure what the boiler is. Can I use a Trane or Honeywell z-wave compatible thermostat? Can the 24V from the AC also feed the boiler when the heat is on?[/quote]

I think you will have to determine why they each have their own thermostat. Was it merely a matter of convenience to the installer at the time, or is there something atypical about your boiler system? If you can take the boiler’s thermostat off the wall and examine the wires and how they are labeled, it should provide answers. Assuming there is nothing atypical, a single modern thermostat ought to be able to control both boiler and AC (I have a basement boiler and attic AC as well). It will be best to have a “C” wire that always provides 24VAC, but many popular thermostats can work without a “C” wire.

watou

3

Most modern thermostats have support for dual transformers.
You tie the common C from each thermostat (The one that is NOT RC or RH) together.
Than you have an RC (Red Cooling Power) and RH (Red Heating Power) from the corresponding transformer.
Often there is a jumper internal to the thermostat for these. You will need to remove the jumper.

The White W usually controls the heating … and is powered from the RH wire.

Depending on the number of Cooling Stages the RC powers the
the fan G, the Cooling Y1 and Y2.

My Trane (Actually RCS) Z-Wave thermostat supports separate RC and RH wiring.

I hope they ran 3 wires for the Boiler thermostat … RH, C, and W. If the thermostat did not need power they may not have run the C wire.