Our marijuana grow space is an enclosed room and we’re using one 1,000-watt high intensity discharge (HID) lamp. It’s becoming difficult to the temperature below 90F even with constantly running fans and an open door during the daylight hours. We also have an air conditioner in the room, but, after half an hour, only hot air comes out of it. Some people have suggested cooling the roots as a solution. What’s your suggestion? Can the marijuana plants make it even in 90F heat?
As long as the roots are kept moist, high temperatures won’t kill the marijuana plant. It will, however, ruin the flowers by making them looser and sparser along a stretched-out stem. Thus, it is vital to ensure that they stay in a room with a temperature of about 70 to 74F (about 24C) with non-enriched air and below 82F (27C) when the air is enriched with CO2.
You can eliminate the heat easily by simply stopping it from gaining access to the room. With an air-cooled light, you can vent out most of the hot air created by the bulb. The air is drawn from outside through a tube is heated in the reflector and expelled through another tube. This air never makes it into the room and is basically odorless.
A single 1,000-watt lamp produces around 3,200 BTUs of heat. A room air conditioner that goes into a window can help move the heat out of the room (either outside or to another space in the building. A portable air conditioner is convenient and can be rolled into your marijuana grow room when needed. It vents the heat out through a 4-inch tube.
Altering the light cycle so that the lights are on at night and off during the day can certainly help. Depending on your location and the season, the temperatures at night could be much cooler than those during the day. You could use cool outside air to vent into the space and the hot air could be removed. Many growers have suggested that cooling or heating the roots works to counteract above-ground temperatures. With a canopy temperature of 85F (29C), the roots would need to be cooled to 65*F to adequately counteract the hot air. With a hydroponic system, you can do this with an aquarium water chiller, but there is definitely a learning curve.