The past few days I’ve been seeing 10-15 degree swings with an analog house thermometer and a digital house thermometer hooked up to my gas Williams vented heater in my greenhouse. This seemed pretty large. Part of the problem seems to be the thermostats don’t adjust quickly to temperature changes, e.g. are too low-pass. Could I somehow hook up something that responded more quickly to temperature swings?
So time to experiment! I did have a heat mat thermostat controller that turns a 120 V electrical plug on and off (designed to warm soil to a set temperature for germination). It has an external thermostat probe that seemed quite responsive. However, the gas furnace doesn’t turn on and off with 120 V, it’s instead a millivolt system that simply closes and opens a circuit to turn the furnace on and off. So I got an AC/DC power relay that converted a 120V electrical socket turning and off to turning my furnace on and off.
This seems to be working a lot better! Less than 5 degrees of temperature swing. This is a pretty simple thermostat so the next step is to try a programmable thermostat that has an external probe. Having it set a lower temperature at night automatically would be quite nice.