Lights and Fans Question

I have a six inch fan that moves 240 CFM. Grow tent is 50 by 50 by 79 inches, so that’s approximately 114 Cubic Feet. (If my calculations are right. So, I’m thinking that’s a good amount of air to be moved in and out and should take care of the higher temperatures caused by the lights. (Especially the HPS)

Two lights. 1 400 Watt HPS and 1 300 Watt LED. I’m thinking that I should have the fan on the same timer as the lights so that I don’t have a fast drop in temperature every night when the lights go out. I also have a couple of 5 inch “corner” fans that fit just right in the bottom of the two fan holes. This fan I might be able to leave on. I’m running temp tests as I type this and it will all depend on what I find in my hourly temperature checks. (None of my good plants are in the grow tent yet, just my two bag seed buddies.)

I’m also thinking I might set the HPS on 75%. I know that’s not exact as far as how much light the plants will get, but it’s closer than 100%. And I don’t think I need that much anyway. I’d just like to see if I can get them to grow a bit faster and bushier with the extra light.

So, my questions…

  1. Fan on full time or with light timer?
  2. HPS on 75% or 100%.
  3. Am I moving enough CFM?
  4. Once the grow is over and I want to use the tent as a drying station, is the fan sucking too much air?



Hey OldGoat
Sorry to get off topic and not answer your question but I an impressed growing set up. I have been reading some of your posts and I think you have a great layout. I am not trying to be a stalker but keep up the great work and ideas. I will use a few of them!

Have a great grow

Thanks, just remember, this is the first time since 1974 that I’ve tried to grow inside. So, I’m not the expert here.


Ventilation setup:1 - 6 inch duct fan rated at 240 CFM on the top 10 inch access opening. 6 inch foil duct. ( I bought 25 feet, and it was plenty for me. But the room is very small.) 1 - 2 by 6 cut to 19.5 inches long. (This is what’s between the AC and the window and allows the vent to go directly outside) 2 - utility fans, 5 inches 1 on the back side 8 inch access opening. The other available if needed. (CFM unknown, doesn’t feel like a lot.)

Still seeing 81 Fahrenheit inside the tent. Added another foil duct running from in front of the AC (duct taped of course) to the little fan in the back.

I guess what I’m learning today is how to control the grow tent temperature.

Oops. Yeah, you heard me. Oops. I messed up. I have a heater in the tent that I set the thermostat to 72 degrees. It keeps the tent from getting below 70 when the lights are off.

Guess what I found when I went inside to try to figure out why it’s staying so hot in there? Yeah, the thermostat was set to 82.

So, lesson here is, check everything before you leave the tent. Every time.

Yes; You cna use the tent to dry and cure the yield. All you need is darkness, and air movement.

Fan should be linked with a temperature / humidistat. This will allow you to set the temperature, and humidity levels you want the ventilation system to turn on at.

Cool. I can get more toys… :wink:

You probably want to get a 1000 watt for running at 100%