Saving Hundreds with a DIY Underfloor Heating Thermostat

Underfloor heating is a very nice amenity. In a tiled bathroom, it can keep the floors warm and comfortable. When installed throughout a house, it can heat the entire home. Some research suggests that this is more efficient than typical ducted central heating systems, which tend to concentrate hot air high up around the vents. Many underfloor heating systems work by running hot water through pipes in the floor and that requires a thermostat. To bring their home into the 21st century without spending hundreds of dollars, Redditor JoeCartersLeap built their own DIY programmable thermostat for their underfloor heating system.

JoeCartersLeap's home has an older underfloor heating system that uses a 0.75A AC motor-driven pump to push water through the pipes. A rudimentary thermostat controls that pump, but it is very basic. It is an analog unit that is imprecise and certainly doesn't offer any connectivity to the IoT or home automation ecosystems. JoeCartersLeap wanted a more modern thermostat, but found that the products on the market cost several hundreds dollars. And they leave something to be desired even at that price, as they receive power from a battery or parasitically.

So JoeCartersLeap decided to make their own modern Wi-Fi-connected digital thermostat and it only cost them around $40. It uses an ESP8266 to control the pump motor through an SSR (solid-state relay). Power comes in via a USB cable and the ESP8266 monitors the temperature using a DS18B20 sensor hidden under a rug. The ESP8266 shows the target temperature and current temperature on a small OLED screen and also connects with a Blynk Legacy app for IoT goodness. A simple rotary encoder on the thermostat enclosure lets users adjust the temperature without going through that app if they don't want to.

To eliminate any potential safety issues, JoeCartersLeap wired the SSR in series with the original thermostat. They then set the original thermostat to a very high temperature. The idea is that if the new thermostat fails to cut power to the pump motor for some reason, the old thermostat will do so when the temperature climbs past the higher threshold that a user would never intentionally choose.

This is a great example of a practical project that saved the maker a significant amount of money by filling a gap in the market.