Thermostat for Bathroom Fan Heater

[Razoo]

As this is primarily a thermostat question, I wasn't sure whether to post it in Home Automation or Plumbing and Central Heating.

Apart from the central heating radiator, there is a 2.0kW flush-fitting, wall-mounted fan heater in my bathroom. The fan heater is simply controlled by a ceiling mounted, corded on/off pull-switch, although the circuit is also interlocked with the bathroom lights, so when the lights are turned off, the heater turns off.

I have been unable to train my children to switch the fan heater off once the bathroom has warmed up and they leave it running continuously wasting electricity. I therefore intend to fit a tamperproof thermostat so the heater will turn off before the bathroom reaches gas mark 6.

My question is which thermostat to buy; bi-metal or bellows electro-mechanical, or electronic?

I'm tempted to go for electronic as the bathroom will be steamy at times and this might corrode the bi-metal sensing assembly.

Two thermostats that I'm considering are:

1. Honeywell T6360B1069 (Bellows temperature sensing mechanism).

2. Horstmann HTT4 (electronic TPI control).

Does anyone have experience of either of these thermostats, or is there another thermostat that might be better for my application? Although I don't need TPI (Time Proportional & Integral) control, I think it should work OK with the fan heater.

Thanks,
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Razoo

 

[JohnD]

if those are ordinary central heating thermostats, it is most unlikely that they will be capable of safely switch a 2kW electric load.

It's unusual to have such a heater controlled with a light switch. I hope it is not on the lighting circuit, and that the switch is not an ordinary lightswitch.

This one
https://www.tlc-direct.co.uk/Products/HOHRT3.html
will switch 10A, though I don't know that it is suitable for use in a bathroom. I'd be thinking about a timed switch.

This one
https://www.tlc-direct.co.uk/Products/SATLM2453.html
will switch 16A and has concealed setting.

 

[flameport]

Most of those wall mounted fan heaters have a thermostat built in, with the adjustment control concealed inside the casing.

 

[Razoo]

Thanks for the replies.

The heater is not directly controlled by the light switch and it is not on the lighting circuit. It's on it's own dedicated circuit protected by a 16A mcb. The fan heater circuit is interlocked with the lighting circuit. The heater load is actually switched by a 20A interposing relay. The interposing relay coil is energised by a combination of both the lighting circuit being on and the pull-switch being on. The pull-switch is a 6A device.

The thermostat will also be wired into the coil circuit of the interposing relay, so the thermostat will only be switching a few milliamps, rather than the heater load of ~10A.

There was a version of my bathroom fan heater available with an integral thermostat, but that's not the one I purchased! I fitted the interposing relay in the space that the integral thermostat would have occupied. All my heater came with was an internal, bi-metallic over-temperature cut-out.
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Razoo

 

[Razoo]

This one
https://www.tlc-direct.co.uk/Products/HOHRT3.html
will switch 10A, though I don't know that it is suitable for use in a bathroom. I'd be thinking about a timed switch.

Unfortunately this thermostat isn't tamperproof, so it will be interfered with for sure

I did consider using a timer to set a maximum 'heater on' period, but I would really prefer temperature control. Anyway, it wouldn't take the kids long to discover that if they switched the heater 'off' and then back 'on' again, the timer would most likely reset.

This one
https://www.tlc-direct.co.uk/Products/SATLM2453.html
will switch 16A and has concealed setting.

This thermostat looks OK, although overkill at 16A contact rating. I guess it's a bi-metallic sensor with a shunt heater?

I'm still tempted by the Horstmann HTT4, if anyone can recommend it.
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Razoo

 

[ericmark]

There are 100's of thermostats that will do the job. I use thermostats to control my fridge/freezer to brew beer, these have sensors which are remote to the control panel so bit in the bathroom would be ELV. The InkBird ITC 308 is very easy to adapt for nearly every temperature control problem. The STC-1000 was the unit used but the Inkbird does not need an enclosure.

However I would not be looking at a temperature control but a timer, the simple push for up to 15 minutes switch will likely do what you require, keep it simple. If they want more than 15 minutes then they press it again, but any thermostat will still keep the heater running if lights left on, so time would seem a better option.

 

[EFLImpudence]

I have been unable to train my children to switch the fan heater off once the bathroom has warmed up and they leave it running continuously wasting electricity.

Depending on their age that may be reasonable - or not.

Unfortunately this thermostat isn't tamperproof, so it will be interfered with for sure.

Bodes well for the future.

 

[ban-all-sheds]

I have been unable to train my children to switch the fan heater off once the bathroom has warmed up

Try harder.

 

[Razoo]

However I would not be looking at a temperature control but a timer, the simple push for up to 15 minutes switch will likely do what you require, keep it simple. If they want more than 15 minutes then they press it again, but any thermostat will still keep the heater running if lights left on, so time would seem a better option.

Thanks for the thermostat info.

My originating post was only intended to identify a suitable room thermostat for use in a bathroom (outside of zones). I deliberately kept my description of the fan heater control circuit simple, as I didn't think it was particularly relevant to my enquiry.

However, I seem to be getting dragged deeper and deeper into the fan heater control logic... !

Modus operandi:

The corded fan heater pull-switch is actually a momentary device that signals an impulse relay. The impulse relay controls the 20A interposing relay that in turn switches the heater load.

If the fan heater pull-switch is operated whilst the bathroom lights are off, the fan heater will not operate.

If the fan heater pull-switch is operated whilst the bathroom lights are on, the fan heater will operate.

If the fan heater pull-switch is operated again whilst the bathroom lights are still on and the fan heater is operating, the fan heater will be switched off.

If the bathroom lights are switched off whilst the fan heater is operating, the fan heater will also be switched off. The fan heater will not operate if the bathroom lights are switched backed on again, unless the fan heater pull-switch is also subsequently operated.

The fan heater will only switch on if the bathroom lights are already on when the fan heater pull-switch is operated - the fan heater will never switch on just because the bathroom lights have been switched on

When wasteful child exits the bathroom having spent 3-hours bathing and putting on the slap, she doesn't have to remember to switch the fan heater off because switching off the bathroom light will switch off (and reset) the fan heater circuit. This feature will be particularly relevant when the fan heater is being cycled on a thermostat, as it will not always be apparent that the fan heater circuit is on.

The benefit of the thermostat over a timer-controlled circuit is that if the CH radiator has already warmed the bathroom up sufficiently, then the fan heater won't come on at all, thereby saving the pennies.
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Razoo

 

[ban-all-sheds]

When wasteful child exits the bathroom having spent 3-hours bathing and putting on the slap, she doesn't have to remember to switch the fan heater off because switching off the bathroom light will switch off (and reset) the fan heater circuit.

Will she remember to turn the light off?

 

[flameport]

if the CH radiator has already warmed the bathroom up sufficiently,

If the bathroom has a radiator, sling the fan heater in a skip and save even more.

 

[ban-all-sheds]

Unfortunately this thermostat isn't tamperproof, so it will be interfered with for sure

In a location only you can access (or know about) install one with a remote sensor, and put one of the dummy ones they use in offices on the bathroom wall.

I'm still tempted by the Horstmann HTT4, if anyone can recommend it.

They're a good make - I've got an HRT2 in the bathroom - been there for years, still working fine.

 

[Razoo]

In a location only you can access (or know about) install one with a remote sensor, and put one of the dummy ones they use in offices on the bathroom wall.

It's an idea to consider

They're a good make - I've got an HRT2 in the bathroom - been there for years, still working fine.

I've just discovered that Plumb Centre are currently running a promotion on the Horstmann HTT4 tamperproof room thermostat (PC Product Code: 301620). I've just bought one for £14.20, which is about half-price. Bargain!
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Razoo