same lol hence october - april using the heater lol
my electric bill is always very low because i have oil furnace and my water boiler is heated by furnace
i just remember when i first got one of those electric oil heaters my bill went from 60-90
maybe not exact . now that i grow its about 110-150 over summer to winter which is 3 tents lol
its may and still put it on over night lol
I use a heater but also put foam board under my tent. This seams to help a ton.
Good idea on the foam board @Tugthepup
what i have had to do was put my tent on a pallet
i really think two pallets would be better .
i am growing in the basement . under ground x concrete foundation.
having multiple tents with light schedules staggered helps ! i also dump the exhaust in the room
Why are you trying to get such high temps?Are you trying to max the grow out ?I never do good with higher temps it’s always a yo-yo effect and it left me chasing my tail.
You need some of that thick blue styrofoam under your tents, the way you got them set up s allows the cold air to circulate all around them.a few sheets on the walls would also benefit you greatly! 
Try to implement alternating or overlapping light cycle intervals between your tents. So, that always a light is running. The lamp with the biggest heat output (most probably the flowering tent) has to run at night time when it’s colder.
Oh, yea - same situation.
Grow autos, keep the lights on 24/0 or 20/4. 
