Fan timer/thermostat input needed

In process of designing my future grow space which is a converted 9x8 potting shed and not sure what to do about my vent fan. It already has a 16" 1/2hp fan with louvers on one end at the top of the wall and I plan to put 2 or 4 6" ducts on the opposite end at floor level for cross ventilation. I was thinking I could have the fan come on every 15 minutes or so on a simple timer to chage out the air and freshen up the co2 but not sure if this will deal with any heat issues that may arise (starting with 600w hps). I have seen some thermostat controlers but then if it is a cool day or the light is off the fan won't come on to change out the stale air. Is there a repeat cycle timer with built in thermostat control I can get?
Maybe I'm over thinking it but want to have a solid plan in place before I put babies in there.
Thanks in advance.

I had a similar idea of doing the same thing for a friend of mine here in the United States, but having no idea of what country you are living at, nor what type of electrical service you have, I can only comment on what I was planning to do for a 6" Vortex fan that is power by 120 volts. I was planning on using a SPDT relay. For those who are familiar with wiring a SPDT relay, there are five terminals on the relay (consisting of one "normally-closed" terminal, one "normally-open" terminal, one terminal called "common", and two terminals for the "relay coil"). The neutral wire (white wire) would be connected to one side of the relay coil and also connected from this same terminal on the relay coil to the fan neutral terminal. The black wire from the fan power terminal will be connected to the COMM terminal on the relay. The black wire from the temperature controller will be connected to the terminal on the other side of the relay coil and also connected from this same terminal on the relay coil to the N.O. terminal on the relay. The black wire from the timer would be connected to the N.C. terminal on the relay.

Thanks for the input, I am in South Carolina and running 120v. I understand relays but don't see how that helps me control the fan with both a timer and a thermostat. The fan is actually already tied to a temp control although backwards (comes on when temp is below set value) but that is easy to fix. Maybe I just didn't understand what you are saying.

nomoresnow said:

In process of designing my future grow space which is a converted 9x8 potting shed and not sure what to do about my vent fan. It already has a 16" 1/2hp fan with louvers on one end at the top of the wall and I plan to put 2 or 4 6" ducts on the opposite end at floor level for cross ventilation. I was thinking I could have the fan come on every 15 minutes or so on a simple timer to chage out the air and freshen up the co2 but not sure if this will deal with any heat issues that may arise (starting with 600w hps). I have seen some thermostat controlers but then if it is a cool day or the light is off the fan won't come on to change out the stale air. Is there a repeat cycle timer with built in thermostat control I can get?
Maybe I'm over thinking it but want to have a solid plan in place before I put babies in there.
Thanks in advance.

Click to expand...

Those LUX thermostat-outlets can be set to cool and thus supply the power when temps get above a certain value.
Edit: see you mentioned that possibility. My winter grows in a semi-sealed room in an unheated barn only ran the exhaust four times a day for 15 minutes and had no CO2 evident issues. Co2 also is not needed in veg so that might factor in.

Now that I had more time to giving the idea more thought...the idea I have previously given using a SPDT relay would be a bit inappropriate in your situation because of the higher amperage demand of your 1/2 hp motor, and also would be unnecessary to have a double throw relay because there isn't a need in your situation to isolate any back-feeding from the temperature controller circuit into the timer circuit. Isolating the temperature controller from back-feeding into timer circuit would only be necessary when the same timer is being used to power the fan and the trigger cord for a lighting controller (to prevent the lights from coming back on when the temperature controller switch on). Your particular situation would only require a much simpler solution using a SPST (single throw) relay to switch power to the fan. In your present situation you will need to remove your temp control from the power feeding to the fan. Power to your fan will only be switch through the contact on the SPST relay. The temperature controller and the timer can then be wired in parallel to the "relay coil", thus performing the pilot switching of the relay coil.

My exhaust fan is tied into a thermostat as well. The easiest solution I've found to get your fan to kick on and exhaust that stale air during lights off, is to throw a small space heater in the room that is on a timer to come on as soon as my lights go out. My exhaust fan is set to 74 degrees. So once my room warms up it will kick on and exchange that air untill the temp hits 70 and then it'll shut off again.

In my particular case, I never did put my plan into practice as I decided to scrap the idea. I ended up deciding that buying and installing a separate fan on its own separate circuit seem like a more practical solution in my situation.

Stevie51 your suggestion sounds like a winner. It seems like having the timer and thermostat wired in parallel would cause some sort of back feed issue between the two but I am not an electrician so what do I know.

Thanks so much, this was my last hurdle in my grow shack planning so I'm going to go get a SPST relay and wire it up!

When I first read your post Thursday, I had a gut feeling that your post would get plenty of views, but would get no reply. Your post started out asking "Is there a repeat cycle timer with built in thermostat control I can get"? I don't know of any on the market, perhaps there isn't enough demand for a manufacturer to make and sell one on the market. I can say this; you didn't get any reply to that question nor any alternate solution from an electrician. Perhaps an electrician would be hesitant to reply, not knowing how much electrical knowledge you have to accomplish the task, but I can say this; it put you and me in a predicament to find a DIY solution. I'm not an electrician by trade, nor have I actually tried doing what I had suggested, but based on my electrical knowledge I see no reason why it can't work and it may be worth a try. Be sure that the SPST relay you get is rated to handle a 1/2 hp motor.