Burrr its cold at night

by Joe
(B.C., Canada)

How do you regulate proper temps in a cold climate? I have an 8 inch vortex running on low. I also have a heater in my room that turns on when the lights go off. Now, here is my problem: The vortex doesn't shut off. It's filtered before leaving and I want to keep it that way. I have an oil filled heater that is 1500 watts. It doesn't do much when the 8 inch is on its lowest setting. Now, I can't turn off my outtake because of smell and humidity. I have a dehumidifier, but don't want to turn it on because of the wattage. What can I do to make my room optimum? It's currently 15 C when the lights are off, and 21 C when they are on. Room is 12x9x8 and temps outside are 8-12 C.

Answer: Joe- two things make this a tricky problem to fix....One, you don't want to shut off your exhaust fan, and Two- you don't want to turn on your dehumidifier. Living in B.C., it is probably difficult to find a source of "dry" air to use as intake for the garden. Without a dehumidifier, you have two options. One- increase the air circulation around your plants by adding one or two 12 inch oscillating fans. Air circulation is just as important as air exhaust, and plants can tolerate higher humidity without any ill affect as you increase the air movement around them.

Why is this the case? Because plants do not have lungs. They exhaust oxygen and water vapor (humidity) from tiny holes in the underside of their leaves. The humidity and oxygen tend to hang in the air around the leaf causing all kinds of problems, from powdery mildew to rot, unless you provide a source of air movement around the plant. With tighter, more compact plants this problem is especially a problem. Increasing the air circulation helps to move exhausted water vapor away from plant tissue and provides them with a fresh breath of much needed CO2 rich air (thereby warding off the aforementioned mildew and rot).

My other suggestion would be to make sure you are growing plant varieties that can tolerate higher humidity levels.

There is one more thing to consider as far as humidity goes. Warm air is able to hold more water vapor than cold air. As the temperature drops in a grow room, you will notice the humidity increase....until the air can hold no more and the excess begins to condensate out onto the walls and plants inside. This is usually how problems like powdery mildew get their "foot in the door" so to speak....especially if you do not have adequate air circulation in the room.

With this in mind, if you are able to prevent (or significantly reduce) any drops in temperature, it would go a long way towards making the humidity a "non-issue". Having the room well insulated will help prevent some heat loss, but the real culprit is likely the exhaust fan. Constantly on, the fan becomes a constant source of heat loss. The only way to combat heat loss is to either prevent it, or to add more heat. Adding more heat will cost more money....so much more money that it would be more affordable to shut off the exhaust fan and run the dehumidifier (which I realize you do not want to do).

If you have a large enough indoor air volume to draw on for your air intake, than it becomes possible to exhaust your air back into the house (preferably into a different location, where it wouldn't make its way back into the grow room so quickly). Re-circulating air in this fashion would eliminate a lot of heat loss, and would reduce the costs associated with replacing all of that lost heat. On the other hand, exhausting humid air into your home and re-circulating it can be a recipe for mold. As I mentioned before, the money you save should more than cover the cost of running the dehumidifier....but that only solves the humidity and heat problems.

To make a re-circulating air system work, the air volume you are exchanging with needs to be large enough that your garden plants will not be able to deplete the CO2 levels. CO2 is replenished naturally in a number of ways. People breathing. Pets breathing. The pilot lights on your gas stove and gas water heater burning. Also the natural air exchange rate of the house itself. The only thing to worry about, besides keeping the humidity in check, would be your odor concerns. For that, you would have to add another fan and carbon filter. Re-circulating the air inside your grow room (through the Carbon filter) should help keep things in check until the air is finally exhausted through another Carbon filter to its final destination.

Unfortunately, when it comes to proper indoor climate control, there are not many inexpensive solutions. Keep the heat in your room as long as you can, and only exhaust when absolutely necessary. Do other things to make exhausting less necessary (increasing air circulation around your plants and/or constantly pushing the air in your grow room through a carbon filter). I hope this helps, and Happy Growing!