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You need heat, that means more lights, and if you can afford it a CO2 generator should be considered. You could use a water-cooled co2 generator like a HydroGen, but recover the hot water into a tank or two in the room. A couple hundred gallons of 140* water would make a nice heat sink but could add too much humidity. Your flowering room is tricky, but I would do a chain of 3-4 1000w lights, no air cooling (but get air cooled hoods/glass in case you need it in the summertime.) You should be able to light 5-16 plants per light, depending on if you veg them for 3 weeks or 1.
A regular co2 generator can be powered by propane or natural gas, if you have a gas furnace or gas water heater nearby then that's dandy. Since your room should be airtight, this co2 replenishment would be a neccessity, but also adds anywhere from 6K BTU to 36K BTU of heat. CO2 rooms should be around 82-85*F for maximum benefit anyway, and if it gets too hot an exhaust fan can cool the room back down. I'd recommend a green air or sentinel generator and a sentinel chhc-1 environmental controller, they really can run all the atmospheric controls of your room (including co2) automagically for you. Well worth their price.
Anyway, you need 50w per square foot of grow room, but don't forget to account for plants that double in size in stretch, and walkways so you can actually reach all of your plants easily. If you can't reach some, those plants will suck.
Keep pots/buckets/trays off the floor, but pallets are cheap (or free) at tons of places, give you room to run hoses through them, and you can pack them with fiberglass batts of insulation if you want, but I don't like much on the floors of grows because you WILL have a soil spill, reservoir overflow, or leak that floods the floor at some point. Many things never dry well and then mold/mildew/bacteria/bugs invade your room, so you want something you can spray with a pump sprayer (Physan20 or bleach solutions) between crops at the least. Being able to hose out a room is a joy, and if you have hot water you can hose with mores the better.
Yes insulate the walls with mylar or white poly-faced thick styrofoam (rigid insulation) and tape all the seams so it's sealed tight. Kinda expensive but it looks tidy, make sure it nails to studs on all edges, and screw the sheets up with long screws and big fender washers. 2-4" insulation is sold at Lowes/Home depot.
Monitor temperatures closely with a thermostat (the remote sensor ones are really handy so you can watch from your living room) and if it drops below about 68 I'd want a heater turning on.
If the lights and CO2 don't keep it above that temp, then you need more insulation and/or a heater. All of this is going to add up to a lot of power draw, so you need to make sure you have an excess of available 240V and 120V circuits in your basement. Run your scrubber open (no ducting) and it will keep your room pretty odor free.
Sealed room.
Dehumidifier adds heat.
Co2 burner adds heat or use tanks to avoid the humidity.
Or
Slow down your fans to the minimum needed for fresh air exchange which isn't much, and use a dehumidifier and heaters.
Got room to throw a wood stove in there? Provides heat, ventilation, and smell cover. You probably already burn wood right? But would also be a pain in the ass to keep consistent.
I dont know if this will help you, but here is how I solved my winter problem:
I pulled air in from outside, then ran it directly over an air cooled 1000w and vented into the main room. By controlling the CFM's going over the bulb, you effectively control the temperature as well. I found that depending on CFM I can raise the exhaust temp anywhere from 20-60 degrees... so in dead winter at night a low cfm will still be pumping out nice 70 degree air for the main room.