Grow Room Heat Problems

by Karl
(Lehigh Valley, PA)

My question is which way to handle high heat in my grow room. First a couple of facts:

Room is 9'x5'x7' 315 cubic ft
1 Metal Halide 400, 1 High pressure sodium 400
Aeroponic 20 and 2 DWC systems
Temps 90+ with closed doors, can maintain 84 with bathroom style exhaust fan (50 cfm max.) osc. fan inside, and two window fans at the door blowing air in off concrete basement floor.

As I see it I have 2 options:

1. Cool the lights- Put Glass into the lights (they are made for this) and run a 4" duct from 1 light to the other, and then to the exhaust fan (what size fan needed is a question I have.)

2. Cool the entire room- use a centrifugal fan (or squirrel cage fan) hooked to 6-8" duct and vented outside.

I believe I would like to move double the air in the room, so 630+ CFM

Which is the better option? My tomatoes grown inside this have to be better than my neighbors grown outside in a Topsy Turvy. The Cleaning of a common area depends on it. Thanks, KARL

Answer: Karl- even the best centrifugal fans with a high CFM rating will still only be able to keep the grow room about ten degrees over the ambient air temperature. If it is 75 degrees outside, than the best you can hope for is about 85 degrees (if using only fans). The reason is because grow lights heat your grow room in two different ways....

The first way is by heating the air in the grow room directly. Much of this heat can be directed out of the grow room by ventilating your grow lights separately from the rest of the grow room, and by running exhaust cycles on the rest of the grow room often (or continuously). The second way your grow lights heat the grow room is by convection. Even with separate fans exhausting your grow lights and the grow room, your lights still produce infra-red waves (in addition to visible light). When these waves hit the walls and floor (and anything else in the grow room), they tend to warm up the walls, floor, etc..

This is the main reason many indoor gardeners pack up their hobby for the Summer. The only solution is to find a source of cool/cold air that you can pump into the grow room. During cooler months, this air can come from outdoors. During the Summer, however, the only solution is to add air conditioning. Finding strains that do well in hot temperatures may help, but in reality you never want the temperature in your hot spot to go over 82 degrees (let alone the rest of the garden).

Hope this helps you out, Karl. Be sure to read my page on temperature and plant growth for more complete information on the subject, although I have covered the gist of it here! And Happy Growing!