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Home Assistant Heating Controller

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. 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 HomeAssistant. Sadly, this option would cost about £300.

Home assistant to the rescue, it has a built-in integration for controlling heating, so long as you provide it a switch to toggle the heating, and a sensor to read the current temperature. It even has a nice interface.

What are we contending with? I have a combi-boiler hooked up to a pair of Honeywell thermostats.1 Both thermostats are set up to bridge the ‘request for heat’ control line on the boiler. Here’s what the thermostat receiver looks like for my underfloor heating.

This solution doesn’t please me, though. I’d need to separately have a mains to 12v power supply to control something which is switching mains voltage. A quick search didn’t yeild anything satisfactory with an integrated power suply, so I am left with only one reasonable choice: build my own at significant expense and time cost, negating any cost saving from not buying the expensive Hive thermostats in the first place. Okay, it’s not quite that bad, the BOM for each of these boards comes to about £50 in small quantities so it’s still a lot cheaper, and it can probably be optimised a fair bit. And no price can be put on the enjoyment I get when designing a PCB.”

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