On 27/11/2020 13:55:42, Caecilius wrote:
I've got a large house with gas central heating which I use during the
day. It gets cold overnight in the bedroom though, so I use a 2KW
electric convection heater with the thermostat set to about 18 C on a
timeclock which switches on between midnight and six am (boiler comes
on again at six).

This was a great improvement last winter, and it only uses one or two
KWh overnight which must be cheaper than heating the whole house with
gas.

This year I want to improve the solution to keep the temperature more
constant (there's a big hysteresis on the convection heater
thermostat) and remove the bimetallic thermostat clicking noise.

I think I want electronic switching to remove the clicking noise and
allow a lower hysteresis plus an external temperature sensor. Maybe
something that's closer to a temperature controlled dimmer switch
instead of a standard bimetallic thermostat.

My plan is to put this temperature controller between the timeclock
and the heater, and set the heater thermostat to something like 25C as
a fail-safe.

Has anyone found or built something like this? I'm sure I can't be
the only person who want a constant overnight bedroom temperature
without running the main house heating.

Some thermostats have an "accelerator" heating resistor next to the
bimetallic strip. This reduces the hysteresis and make it more PWM based.

If you want accurate control then you're in the realms of PID control
and something like this:

https://www.amazon.co.uk/Hilitand-In.../dp/B07HJ5GQ2L

I have used similar controllers in kiln applications where ramp and soak
functions are required.