I live in ontario, and i am moving into a new house with a work shop at the back of the house. i plan on puttin my cab unit bak there but i am worried about the temp issue. this room isnt heated and it is a cold room. would running a "sealed room": where i scrub the air, then exchaust it back to the cab. save enough heat so i wouldnt need to run a heating unit? i have never ran a sealed room so i have no idea if this would work.

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Mr.Blue

Does the work shop have walls, a roof, and closable windows and doors? (is the interior protected from the elements?)

I flower in a 2.5m x 3.5m outdoor shed, (without additional cabinet) and temps are getting down in the 30's overnight, so am forced to use a heater on the next to lowest setting.
A little trick I discovered last year (sometimes it takes me a while) was to have a dedicated fan near the ceiling above the grow, that forces the warm air back down, directly onto the crop. Works great, and not nearly as expensive to keep warm, as without the fan recirculating the heat that has risen.

Setting up your growroom to 'dry-run' a few nights of actual growing conditions could help steer you in the right direction, since we dont know how big or drafty the shed is, or how cold y'all are getting at night...

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You know, maybe... another take on this...

You can install a small fart fan on the top, then have the duct run down to the bottom of the room.
Same idea... just, complicating things a little bit more.

Mr. Blue, as Rusty Trichome said, try and do a "dry run".
That will help you nail down the temps.