Friday, March 15, 2019

Controlling a portable electric heater with a Nest Thermostat

Nest E thermostat with heater and control box

My love affair with the Nest E thermostat continues (see previous post).  I acquired a second one for about $80 for use in my bedroom that is heated exclusively by a portable electric heater. I'm using a 1500W Pelonis Safe T Furnace with a ceramic heater core that works very well.  Apparently these heaters are classics now - I have had mine since the 1980's! 
Pelonis heater and my relay control box
The relay box contains a 24VAC relay rated for 15 Amps and a 20 Amp circuit breaker.  I wired it with a 12 gauge power cord and a 3-prong grounded outlet for the output.
inside my thermostat relay control box
I put a neon indicator next to the outlet so I could be sure it was switching.

Here's the schematic:

This should work with any thermostat, but use at your own risk.  It is important to use 12 gauge wire in the box and power cord to carry the high load, and I felt better putting my own 15 Amp circuit breaker inside.
Among the things that I have learned to love about the Nest are that it automatically adjusts for daylight savings.  But also it can set back the temperature when I leave home by using the IFTTT app.  Plus it could not be easier to use, program and adjust.  And of course I have connected it to Alexa so I can adjust the temperature by voice command and from my phone from aywhere.

1 comment :

  1. The contacts in my 15 amp relay eventually failed due to the high load. So I replaced it with a 25 amp solid state relay mounted to a metal cover for the box with a large heat sink on it. The relay gets quite hot when it is running 12 amps! But that extra heat just goes to heat the room anyway.


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