Cooling Your Marijuana Grow
When you’re growing in an enclosed space, especially if you’re using high intensity discharge lights that produce a lot of heat, you’ll want to have a good cooling system set up for your growing room.
Cannabis can withstand some pretty hot temperatures, so your grow room can be up to 80 degrees (although that’s pushing it a bit), but a single HID light in a small room can push temperatures over 100 degree Fahrenheit. Too much heat will kill your plants or prematurely cook your harvest, especially during the summer, so plan ahead.
Ideally, your grow room shouldn’t get hotter than 75 degrees during the day. Although cannabis can withstand hotter temperatures for short periods of time, it isn’t good for your plants. As a good test, consider your own level of comfort: if you feel too hot in your grow room, chances are good that your plants are overheating too.
If you’re using a HID light, like the metal halide or the high pressure sodium, you can get an air-cooled sleeve that will go a long way toward keeping the radiant heat (that’d be the heat you can feel emanating down onto your plants) from toasting the canopy of your grow.
An air-cooled sleeve is a glass tube that surrounds your light bulb and allows a fan to blow cooler air through the tube, cooling the light and dispelling the heat through the opposite end.
Still, proper ventilation requires that cool air comes into your grow area, while hot air moves out. Of course, if you’re moving hot air out of your growing area, you’ll need to consider the smell as well. Short of living in a very remote area or something similar, you will need to install a carbon filter at minimum to cleanse the smell of your growing marijuana.
Filtration aside, if you find that your grow room needs cooled, you’ll need an intake duct and an exhaust vent. The intake duct will bring in your fresh, cooler air, and should be located lower down toward the floor of your grow. Your exhaust vent / duct should be located on the opposite wall of your grow area from the intake duct, and preferably higher up toward the ceiling.
Heat naturally rises, so having your exhaust vent higher up will make it easier to cool your grow room. Each of your vents, the intake and exhaust, will need to be equipped with a suitable fan, as well. Intake and exhaust fans are rated by the amount of air they move in cubic feet per minute (CFMs) and you’ll generally want your intake fan to only be 25% as strong as your exhaust fan.
Another trick to keep your grow room cooler is to run your lights at night instead of during the day. This isn’t as feasible during the vegetative stage when your plants need 16+ hours of light per day, but during the flowering stage when you are on a 12/12 rotation it is more doable.