OpenEnergyMonitor Community

emonPi to control space heater


I’ve been reading a lot of the emonPi documentation and trying to figure out the best way to control a smallish 500w convection heater.

I’m in the UK and I’ve got a solar PV array and what I’d like to do is to switch on the heater when I start to export power from the solar PV. The heater is in a room which already has a central heating radiator but sometimes we use the heater to boost the heat a little if it gets cold in there (huge patio doors probably need replaced at some point). The emonPi seems like a pretty neat little project to divert some excess solar into heating the house, even if just a little.

Using the emonPi to measure export from my house looks simple enough (just a CT clamp on the wire to the meter) but my main concern is the easiest way to switch the heaters on and whether that’s something that the inbuilt software can handle.

So my questions are pretty simple

  • Can the in-built software (Node-Red I guess) do what I need it to do (ie, switch on when export > 500w but when the socket is on only switch off when I start importing power)
  • What’s the best wifi or rf controlled plug/wall socket to use with the emonPi? I’ve seen a lot of stuff about flashing cheaper plugs to install custom firmware but I don’t really have much in the way of soldering skills :frowning:


Hello @Vaga222 and welcome!

The software on the emonPi is more to do with the monitoring side of things, but can work well in conjunction with Node-Red or perhaps Home Assistant to do the kind of control that you are after.

We generally recommend installing Node Red or Home Assistant on a separate raspberry pi to avoid too many applications wearing the SD card down.

It sounds like a smart plug such as the Sonoff S20 would be suitable, it has a 10A relay so more than capable for a 500W heater. You will want to flash custom firmware, either EmonESP or perhaps Tasmota would be easier when working with Node Red and Home Assistant directly. It should not require any soldering, just some slightly tricky firmware uploading :slight_smile: