Baseboard heater thermostat question

[tmarschner]

Hi there,

I have a 240V wall-mounted convection heater (similar to baseboard heater) with a built-in thermostat. The thermostat is failing and I would like to switch to a smart-home enabled wall-mounted line-voltage thermostat (which I believe it is triac-based). My question is whether I can remove the failing thermostat, leaving the protective thermal overload device in place and wire the heater "core" to the new thermostat. I'm pretty sure the existing built-in thermostat is not triac-based: I tested this with an oscilloscope and a high-voltage differential probe. When the thermostat closes the waveform of the heater core supply is a regular sine wave and is not clipped even when the thermostat approaches the set-point (it's only ever on or off). Can I still use this heater "core" with a triac-based line-voltage thermostat?

Thanks for any help you can provide. I am a semi-educated newbie at stuff like this.

Tom

 

[d123]

Hi Tom,

I couldn't answer, sorry, not a circuit type I'm familiar with, but I think if you posted images of the circuit and the names of the parts (links to any device datasheets if you are familiar with them), maybe someone will be able to give an informed opinion.

 

[c_mitra]

I have a 240V wall-mounted convection heater (similar to baseboard heater) with a built-in thermostat. The thermostat is failing and I would like to switch to a smart-home enabled wall-mounted line-voltage thermostat (which I believe it is triac-based). My question is whether I can remove the failing thermostat, leaving the protective thermal overload device in place and wire the heater "core" to the new thermostat. I'm pretty sure the existing built-in thermostat is not triac-based: I tested this with an oscilloscope and a high-voltage differential probe. When the thermostat closes the waveform of the heater core supply is a regular sine wave and is not clipped even when the thermostat approaches the set-point (it's only ever on or off). Can I still use this heater "core" with a triac-based line-voltage thermostat?

As you are sure that the existing thermostat is simply on-off, you can certainly put it off the circuit. You can use a triac based (like ones used in light dimmers) regulator with the basic heater core of the wall mounted convection heater.
As you mention rightly, it is wise to leave the protective thermal overload unit in place as a second in line.

 

[KlausST]

Hi,

the problem is the regulation loop.
Since the thermal feedback of a room heating system is very delayed .. this leads to oscillation.
Thus usually room heater thermostats have lokal feedback (heated bimetallic switch).

Klaus

 

[dick_freebird]

You can find industrial temperature controllers with pretty
high (high enough?) contact ratings, that would do the
job - maybe batter / more reliably than a cobble.

 

[c_mitra]

Hi,

the problem is the regulation loop.
Since the thermal feedback of a room heating system is very delayed .. this leads to oscillation.
Thus usually room heater thermostats have lokal feedback (heated bimetallic switch).

Klaus

Absolutely right. On the other hand, it is better to control the temp at the destination and not at the source.

The oscillation may not be serious for a room heater (because of the large thermal mass, it may not even be felt) but it can be nuisance in some other application (say for example in a lab thermostat).

Bimetallic switches have large hysteresis and they too will produce temp oscillations. But having the control close to the source has many advantages.

If the load is variable (many people going out and coming in), it is very tricky to control the oscillations. But with a big heater and a good fan, the frequency can be pushed higher.

Good thing is that many of the electronic regulators are proportional controls. They tend to reduce oscillations.