@nprofile1q... @nprofile1q... At minimum I'd look into attaching a thermostat to a vent fan to just draw in exterior air during the winter so you don't have to run a whole heat pump for it. Most multi-head heat pump systems only have one reversing valve for the whole lot, but I have seen at least one where each head has an independent valve for exactly that purpose, yeah. (It was a "net zero building" that was used as a 'functional showroom' to show off a whole bunch of 'green' tech, so they had the Expensive heat pumps)