In some cases where we need extra low voltage wires to control accessories or even air source heat pumps, and we only have two wires available, IO controls has options for us.

IO WR-400 wireless relay, or possibly the IO UT-SWM.

The UT-SWM allows multifunction control over 2 wires. This is typically used when you do not have enough wires between the thermostat location and the Furnace or air handler.

The WR-400 is a 4 channel relay with wireless communication. This item is typically used when you do not have enough wires between the furnace or air handler and the outdoor air conditioner or heat pump. This however will not handle communicating type systems such the ICP ION control or Goodmans climatetalk system.