wiring thermostat to extractor fan

[beanybot]

Hi I have a metal workshop that I am installing a bathroom extractor fan to to aid air flow on hot days (or manually if I want to rid of fumes whatever). Whats the cheapest way to wire the fan through some sort of thermostat that will trigger it to come on when it reaches say 25 degrees, and then back off when it reaches 23 or something like that. I've had a look at fancy, expensive thermostat controllers but just need the most basic, cheapest option for this. I already have power in the workshop, so that's all there already.

This is the rough plan.

 

[Taylortwocities]

Most heating system thermostats are wired up so that when it gets COLD the heating comes on. You need a thermostat that works the other way round = COOLING. Many do. Look for one that has changeover contacts (SPDT) and it is easy to wire up in parallel with the override ("I/O switch") that you have on your diagram.

You will struggle to find a domestic thermostat that has a 2°C level of granularity. House heating systems are more rough and ready.

 

[stem]

You need a thermostat with a changeover contact that will operate a cooling load. (i.e. will turn 'on' when the set temperature is reached rather than turn 'off') Most have this facility, but will be a bit more accurate than +/- 2 degrees.

A reasonable quality thermostat such as the Honeywell T6360B Room Thermostat will do the job and should cost you between £15-£20

You might be able to get a cheaper unbranded one from a DIY shed, but that will still cost you a £10

Alternatively look on here for someone posting to ask how to change an old style thermostat for a fancy new one with lots of features and ask them if they will send you their old one. Then there's always ebay...

Depending on the size of your shed and how hot it gets, you my find that you need something a bit bigger than a bathroom extractor to get rid of the access heat.

 

[beanybot]

Most heating system thermostats are wired up so that when it gets COLD the heating comes on. You need a thermostat that works the other way round = COOLING. Many do. Look for one that has changeover contacts (SPDT) and it is easy to wire up in parallel with the override ("I/O switch") that you have on your diagram.

You will struggle to find a domestic thermostat that has a 2°C level of granularity. House heating systems are more rough and ready.

Thanks. Will look for that. Yeah the 2 degrees was just off the top of my head. Whatever the norm is will be fine.

Something like this? http://www.screwfix.com/p/horstmann-drt1-room-thermostat/53729

The next issue i have is whether this will actually work or not. There are many gaps under the eaves of the roof so not sure if will effectively change the room air or just drag new air in from the closest point in the roof.

 

[beanybot]

Depending on the size of your shed and how hot it gets, you my find that you need something a bit bigger than a bathroom extractor to get rid of the access heat.

Yes thats a concern, its 10x13ft. Im wondering if it will do anything at all as the eaves are not sealed. It's one of these. Yardmaster 1013

In fairness I haven't yet experienced excess heat (its been up a week) but I live in Scotland so maybe this wont be a problem and I need to focus more on heating!

 

[AndyPRK]

There are a lot of concerns with this.

Will the (small) fan actually do anything.

Will a thermostat be over the top. Do you want the fan running when your nit in there. You would probably be better off with a simple switch to start with.

 

[beanybot]

There are a lot of concerns with this.

Will the (small) fan actually do anything.

Will a thermostat be over the top. Do you want the fan running when your nit in there. You would probably be better off with a simple switch to start with.

Well the idea of the thermostat was to do exactly that, ensure the shed and its contents dont get too hot when I'm not there to flick a switch. But as you said, there is a concern over effectiveness. i.e. will there be any.

 

[AndyPRK]

If that's the intent then that's fine.

 

[ban-all-sheds]

... fumes ...

Not explosive or flammable, are they?

 

[ban-all-sheds]

There are many gaps under the eaves of the roof so not sure if will effectively change the room air or just drag new air in from the closest point in the roof.

Could well do that - can you mount one lower down, maybe suspended from the roof?

 

[beanybot]

... fumes ...

Not explosive or flammable, are they?

No, things like welding smoke (not galvy) or if I've had a bad curry the night before. Nothing crazy

 

[ban-all-sheds]

if I've had a bad curry the night before.

That'll be both, then.

 

[flameport]

Bathroom extractor fans are generally made of plastic, not something which will stand up to being used in the roof of a boiling hot shed with welding fumes going through it.

Welding fume extractors need to be far more powerful than any bathroom extractor, and have the inlet duct positioned close to the workpiece - otherwise they will do nothing.

 

[eveares]

Here's an idea, use a Axial fan for the fan as it will suit your requirements.

For the switching, I would use this: http://www.tlc-direct.co.uk/Products/TCWS10.html with a normal switch bypassing it for manual control.

Just make sure the current rating of the motor (including start up currents if induction motor) are within the thermostats and switches limits.[/url]