Research fellow, programmer, and home automation enthusiast Simon Cooksey has designed a handy custom board to help smarten up a dual-thermostat heating system with Home Assistant integration — having found the house's split heating system unsuitable for many off-the-shelf options.
"I’ve been using Home Assistant to automate my house, and one of the big things I want to add control of is my heating," Cooksey explains. "The heating system in my house is a little different to a typical British home in that I have zones, one for upstairs (radiators) and one for downstairs (underfloor heating). This means a lot of the off-the-shelf thermostat options, especially Google Nest, aren't suitable for me, and what options there are have a prohibitive cost. A commercial option would be something by Hive, they support multi-zone thermostats and they are supported in Home Assistant. Sadly, this option would cost about £300."
Rather than throwing money at the problem, then, Cooksey decided to throw time at it instead. Initially, he considered using a cheap Espressif ESP8266-based relay board, flashed with ESPHome for integration into Home Assistant — but discarded that as an ugly hack, requiring a separate power supply. Finding nothing on the market with an integrated supply, Cooksey designed his own — and for considerably less than the commercial Hive alternative.
"I didn’t want to roll my own AC/DC converter or switch mode power supply," Cooksey explains of the finished design, mounted in a commercial DIN-compatible housing, "so I picked a PCB-mount module. The first one I selected was very simple, but regrettably £20 [around $24] ea. I thought about it and decided to deal with a SIP [System-In-Package] module with a higher integration complexity (and board footprint), but that was substantially cheaper at £1.86 [around $2.30] ea, and about £5 [around $6] in support components."
Built around an Espressif ESP8266 module with PCB antenna, the resulting board includes its own power supply, two relays, and a fuse and over-voltage shunt diode for safety — while the ESPHome firmware ties it in to Cooksey's existing Home Assistant setup. One relay can be used to trigger the found floor's underfloor heating, while the other can be used to trigger the boiler connected to the radiators upstairs. In total, Cooksey estimates the bill of materials at around £50 ($61).
More information on the project is available on Cooksey's website, while the Eagle project files are available on GitHub under an unspecified open source license — but come with the warning that there are a few minor bugs in the current design, and that the files "are provided without warranty. I'm not a qualified electrical/electronic engineer," Cooksey explains. "If your house burns down it's between you and your insurer."