Anyone here use a HomeKit-enabled thermostat for in-floor heating? My bathroom has radiant floor heating and it's controlled by a True Comfort programmable thermostat which is a pain to program and use. HomeKit features would be ideal, especially for automations.
Since it's a 120/240V thermostat, I thought the Mysa Smart Thermostat would work, but unfortunately they don't support in-floor heating.
Any suggestions?
A thermostat is just a switch that is controlled by temperature. Being its 120-230v you could wire it to turn on a TV if you wanted too.
The function that would make a 120-230v thermostat incompatible with a 120-230v heating source would be what is typically called 'heat anticipation' generally controlled by the thermostats CPH (cycles per hour) setting. This is the basic logic for the thermostat to turn the heat off prior to reaching its set point. It's anticipating that the heat source needs time to cool off and it will continue heating during this time. Much like the brakes on a car, the faster you are going the sooner you need to start slowing down when coming to a stop, if you don't you will overshoot your target.
Unfortunately electric baseboard is nearly the polar opposite of in-floor radiant. Electric baseboard is heating nearly entirely with convection and since its electric (low mass) it heats and cools quickly. Conversely in-floor radiant is heating mostly with radiation, since its the floor there is a lot of mass so it takes a while to heat and it takes a while to cool.
Professional lines of thermostats have a very wide range you can set this too so the same thermostat can control a heat pump, gas furnace, in-floor, cast iron radiators, convectors, etc etc. However they are typically 24v thermostats, not 120-230v.
I checked Mysa webpage to see if there was setting for adjusting this. And the fact that they are going to introduce a thermostat specifically for in-floor leads me to believe there isn't....
https://try.getmysa.com/infloor
If the wiring is accessible what I've done on a couple occasions (I work in building controls btw) is use a 24v thermostat that is designed for the application (in-floor radiant), a
24v relay and
24v step down transformer (those are overkill because I don't know your setup). Wire the transformers high side (120/230v) to a power source (any) than wire the low side (24v) to the R and C on the thermostat. Wire the coil side of the relay to W and C on the thermostat and wire the normal open set of contacts on the relay to complete the circuit for the in-floor (what the current thermostat is doing now). This just adds a 24v power with relay heavy duty enough to support the current draw of the in-floor radiant.
If that sounds like a PITA its because it is, but it works. In the past I would use a thermostat/control that works best for the equipment its controlling. However now the end user wants a specific feature set (wifi, Alexa, HomeKit, a color LCD, etc etc) which sometimes doesn't exist....or a single company makes it but its a garbage product.
