For indoor marijuana growing, any time of year has its challenges. Like, I live in a place that has very hot summer months. My grow room was in the back of my house, shaded by trees. The electric company sent a crew that trespassed on my property and butchered the biggest tree shading my grow room wall. Huge amounts of sun hit the wall and heated up my grow room all summer.
I was running two 1000-watt HIDs and could barely air condition and vent the heat enough to keep the room under 80F. The heat caused plant problems. I had to quit growing that summer. Friggin’ utility company!
So I looked forward to winter because all that HID heat unwelcome in summer is now a benefit.
With outdoor temperatures where I live averaging 25-40F most of the winter, and the rest of my house other than the grow room set to 65F, I use HID heat to warm the grow room to the ideal growing temperatures of 73-77F when lights are on.
When the lights are off, I use a space heater with a digital thermostat, to keep the room from dropping below 68F. It’s good to have your lights-off temperatures a few degrees cooler than your lights-on temperatures, but if your grow room goes below 68F, and especially if you have high humidity, you run the risk of encouraging powdery mildew or other attackers.
Low temperatures slow down your marijuana plants’ metabolism, growth rate, root development, and nutrients uptake.
Remember also this general concern: electrical load. When I added a 1500 watt space heater to my grow room appliances, it blew the circuits, even though I was on a 20 amp circuit.
Always do an electrical load check and an electrical system retrofit (if necessary) BEFORE you set up a grow room.
Anyways, you can get real creative in how you manage temperatures, air movement, and air exchange in your marijuana grow room and the rest of your home during winter.
When I first started growing marijuana and it was my first winter crop, I saw how my closed-up grow room with two HIDs was too warm. I needed to get some cooler air in there.
Because I live in such a way that I have no unplanned visitors or other security risks, I experimented with leaving the grow room door open a few inches.
I had a tower circulating fan, and a precision hygrometer/thermometer. After a few days, I saw how exactly how much to open the door to mix the 65F house air with the warmer grow room air to create a consistent 72-77F, below-50% humidity environment in my grow room.
During lights-off, I close the grow room door, keep the fan on, and use a space heater to keep the room above 68F.
This program worked well except that it allowed a vector for odor, spores, gnats, dust, and microbes to get into the grow room.
Later on, I installed a high-CFM venting fan connected to a carbon filter. The venting fan was not connected to ducting or tubing that fed to the outside world.
Instead, I sent it into a duct that distributed grow room heat to the largest room in my house.
Last year, a trusted grower friend who has HVAC (heating, air circulation, and cooling) expertise gave me a set of other ideas. These included a better linkage to exploit my HID heat during winter, and installing whole house UV and carbon filtration, which was mediated through my furnace/AC air handler.
When I installed those new systems, the entire house atmosphere was cleaner, the grow room air was purified from floating dust, spores and other bad stuff, there was no marijuana odor, and the heat from the grow room was saving me money because instead of being shunted outdoors, it was staying inside and reducing my overall heating bills.
Another thing I discovered for managing heat in winter and summer is a dimmable digital ballast. It’s called a “low-frequency digital ballast” and I use it along with the Diamond series of high-output digital HID bulbs that are matched to go with it.
This equipment is made with marijuana growers in mind, apparently. The low-frequency thing is so your ballast doesn’t send out radio frequency interference that can be detected by spies or that interferes with appliances, phones, etc. like most other hydroponics grow light ballasts do.
The HID bulbs are designed to provide marijuana the light wavelengths it wants. You can’t find any other hydroponics HID bulbs that are designed for marijuana, as far as I can tell.
The reason I mention this equipment is that the low-frequency ballast is adjustable so I can change the amount of watts I am using. That’s a great tactic for managing heat, and electricity.
Using this ballast, I have the 1000-watt bulb but I can run it at 1000, 750 or 500 watts. The lower settings of course deliver less light and less heat, and vice versa.
If you’ve been using magnetic core/coil ballasts or even digital ballasts and you try this set-up, it’s a world of difference.
Another thing that cold weather did is to force me to look at my attic and wall insulation. There was no wall insulation and the attic insulation was weak, like R-20.
So I added insulation to R60 wherever I could, while also putting baffles, sealers, and a ridge vent and improved soffits to make sure my attic ventilation was just right and that I am not leaking any heating or cooling out of my home.
If all this sounds slightly confusing, or like a lot of work, please take a look at this article that talks about marijuana videos that show you how to build well-ventilated, climate-controlled grow rooms.
Growing marijuana in cold weather gives you many rewards. Even “free” heat! There’s often a shortage of fresh-grown buds that starts a month or two after outdoor harvest season ends, and winter growing gives you a way to have fresh buds while the snow is still on the ground. And when you can use HID heat to reduce your home heating costs and keep your grow room temps where they should be, that’s great too.