> I want it to work with a contact-closure (TT/XX) input to call for heat/cooling. Sure, if you have a fancy thermostat that works better, I'm going to read the

> I want it to work with a contact-closure (TT/XX) input to call for heat/cooling. Sure, if you have a fancy thermostat that works better, I'm going to read the brochure, but I'm not buying it if I find out it won't work with just a dry contact input. > I want it to have an open interface to extract data (similar to the open interface of a dry-contact closure) about run-time, performance, etc. (I will, however, buy it without this.) FWIW, there is a standard called OpenTherm which most off the shelf thermostats support and HVAC systems support. It's a 2-wire serial 2-way protocol, quite simple. IIRC OpenTherm even has a fallback compatibility mode where closing the loop will enable the system at full power, though I am not sure this will work with heat pumps, as they can both heat and cool. You could even rig up a Raspberry Pi or equivalent with an OpenTherm interface and attach it to any OpenTherm compatible heater/cooler to control it and read stats.