Want to control 120 volt bath fan with 24 volt thermostat

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Old 11-24-13, 11:38 PM
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Want to control 120 volt bath fan with 24 volt thermostat

Is there an all in one relay/transformer that will switch on and off 120v via demand called for from a 24v thermostat? I'm hoping to be able to run the 120 to the relay have it check with the thermostat for demand and thus operate a bath fan based on temp. Fan is to be mounted above toyo oil stove and reverse feed air through original trailer ductwork. This will allow toyo to heat entire trailer at about 1/3 the cost. (I hope). Don't want to run 120v thermostat wires 50 ft to the point where thermostat needs to be mounted.

Thanks much if you know where I can find such an animal.
 
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Old 11-25-13, 06:55 AM
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You could do it simply with a 24 volt transformer and a relay.
These items should be readially available from any electrical or HVAC supplier.

I do strongly suggest you also get at least Nema 1 rated box with knockouts ( which I believe should suffice ) to install the transformer , relay and make all electrical connections. You probably don't need anything larger than a 6 X 6 X 3.5 or 4.

This box I would guess can be mounted near the fan and your power supply feed.

I'm not sure what size fan but do you think a bath exhaust fan has enough CFM capacity to move enough air ? And through what size existing duct work ?

Here's a diagram of something I believe should work.
 
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Last edited by canuk; 11-25-13 at 09:03 AM.
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Old 11-25-13, 08:18 AM
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Thanks thats what I'm looking for but was hoping for a specufic model # or two that I could do some comparison shopping for online. Haven't been able to find one that looks like it accomplishes both the transforming and switching.
I'm not sure ill have enough cfm (140) to truly heat the whole place but if it can keep enough heat in a couple of back rooms through the night so as not to have to fire up the original furnace except on exceptionally cold spells Ill be happy. Toyo keeps a good 2/3rds of the place toasty just radiating and with a ceiling fan.
Good thought on the nema box will add that to the list
 
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Old 11-25-13, 08:55 AM
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Thanks thats what I'm looking for but was hoping for a specufic model # or two that I could do some comparison shopping for online. Haven't been able to find one that looks like it accomplishes both the transforming and switching.
I guess it wasn't made clear -- I suggested and drawn a seperate 24 volt transformer and a seperate relay which are far easier to get than an all-in-one unit.

The square around the transformer and relay with the wiring represents the Nema 1 box --- sorry about that


I edited the diagram to show the Nema box.
 
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Old 11-25-13, 01:58 PM
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Fan center relay

Hi, why not just use a fan center relay it can be mounted on a 4" Sq. box, check at the big box stores in the heating isle.
 
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Old 11-25-13, 03:21 PM
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That takes care of the relay. Now a 24 volt transfomer is needed and I'm thinking a 4 inch box would be too tight for them both to fit along with all the wiring.
 
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Old 11-26-13, 05:56 AM
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Google fan center relays and you will find many,they are all made to fit in 4"Sq. boxes
 
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Old 11-26-13, 10:05 AM
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Google fan center relays and you will find many,they are all made to fit in 4"Sq. boxes
Ah --- yes , that would work alright
If you can get them as cheap as $14 or $15 ( the cost of a seperate 24 volt transformer and seperate relay ) that would work nicely.
 
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Old 11-26-13, 12:08 PM
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Solved

Thanks folks you led me to the water and I drank!
Went to a hvac plumbing supply and they too suggested a fan center relay
Bought this
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Wasn't going well using the directions the shop gave me and following the info
on the enclosed installation sheet till I found this online
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By attaching r and w contacts on thermostat to r and g contacts on relay it operated the fan when calling for demand.
Incoming power black wire was connected to both black wires on back of fan center relay
Incoming white nuetral connected to white on back of relay and white from bath fan
Yellow wire from relay connected to black wire from bath fan

Thanks again
 
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Old 11-27-13, 09:55 AM
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Hmmm guess I posted one pic twice that should have been this one
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