Regulating tent heat through air volume

I need a way to raise heat in tent for basement grow. Basement temp. varies 53-64 F . Moving the amount of air in my tent (1meter square x2 meter high) with the 6 inch fan it came with sucks all the heat that the 400W MH makes.
Should I :

A) restrict air inlet or outlet for that matter.

B) switch to 4” fan

C) ( the one I’m currently experimenting with) put fan on timer. 1/2hr ON every 2-3 hrs.

My concern with C is will the temp. fluctuation/cycling affect my growth ?

D) something you can suggest.

While reading the forum, it seems like once my foliage gets under way I will need more airflow and heat removal. But what do I do until the juvenile plants develop that foliage?


Welcome to ILGM.

I would try a in line regulator on the fan that varies the speed and move it to a low setting. It is pretty important to have air flow to prevent fungus in the tent.

As cold as the environment is in the basement, a small space heater placed in the tent might be your best option. That will allow you to keep good air movement by keeping the fan going all the time.


I have a fan that comes with built in controller, one of the factory functions is to ramp fan speed via included temp sensor. I haven’t ran it in a grow yet, so can’t really say how well it does or not. But it has some really cool features, very efficient and quiet too.

I also understand there are some controllers that may do this. But most I’ve seen are a start/stop. It’s probably best to not have a break in air movement like that. Even with a recycle timer, you wouldn’t want to leave it off for anything like hours. More like minutes, if at all.


How strong is your exhaust fan? Do you have an intake fan too? If so how strong is that? Why is the cubic footage of your grow space?

I had this same problem plus low humidity and I solved it by putting my fans on a timer so they run one minute on and then are off for two minutes.

Depending on your space and the size of your plants they can consume the available CO2 in your grow space in as little as 20 minutes. I think the timer idea is a good one, but not for the intervals you are considering.

1 Like

You need a controller for exhaust. When cold i run on low depending on temps in tent may go low or if a lot of heat high

1 Like

Not to step on toes all great advice 3x3x6= 54cf at an exhaust rate minimum of complete exchange every 3 min exhaust could easily be 4" even with 50cfm fan it is more than adequate depending on RH and temps. There are several things can be done to increase temps with just light and fan direct a fan towards light and top of tent this will push warmer air down add Black buckets of warmed water the light will be absorbed by buckets storing radiant heat during lights on releasing it during lights off place exhaust on lights timer so it only runs with lights wrap tent with blankets.
I grow in Northern BC cold is the normal so I know your pain well if you can keep them in 60’s during dark they will be fine


it’s currently -14c with a -18 wind chill and I grow in unheated shed so feel free to tag me in have more than a few tricks up my sleeve :wink:


I use a small 700w ceramic space heater with a temp switch & it works very well, but they are some cool ideas @donaldj :+1: :smile:

1 Like

I use one of these. It will automatically control your exhaust fan and hold whatever temp you program it to hold.

This is a graph of the recorded temp and humidity inside my grow space. As you can see, it holds a very constant temp during lights on as well as lights off.



Try pulling fresh air from outside your tent through your light and back into your tent at the bottom that will give you warm fresh air and have second fan to exhaust tent use speed controllers to dial in and maintain neg pressure…and or maybe a heater set up outside a passive vent… @Greasemonkey