Better to have two 2 x 1.5 x 1.5 m rooms than 1 x 3.0 x 1.5m and alternative 12 hours and exchange air/heat

As above? Does it make sense to split the room in two and have them both on alternative 12 hours and put two fan between the rooms to exchange the air? Would help keep lights off the room warm in winter etc?

Is going to be a sealed room or rooms with Co2 injection os the fans would be to just pass the air.

In short yes it’s a very good idea, I used to use my veg exhaust to heat flower room during lights off

waring192 said:

As above? Does it make sense to split the room in two and have them both on alternative 12 hours and put two fan between the rooms to exchange the air? Would help keep lights off the room warm in winter etc?

Is going to be a sealed room or rooms with Co2 injection os the fans would be to just pass the air.

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Generally id say yes but each situation is different. If your close to your max amps its a life saver. If the environment works out fine (watch out for spiking rh in the dark side!) you generally have an easier time to maintain min and max temp as one side is always on creating some heat but you never have the full power of both sides on at the same time.
Downsides is paying day power prices for half the grow while you could get the whole grow at night time prices. But generally the saving in power cost in this case will get eaten up buy having to run extra climate control during the day.
Other downside would be having to buy doubles of some equipment, for example dehuey, unless youre really able to dial things in and move a lot of air between the spaces.
Another downside is access: each side can only be accessed in its "day" which means you may have to work at night.

CO2 won't matter at night/lights out because the stomata will close and the plants only diffuse O2 then. 1 larger tent will ventilate better... otherwise, it makes sense to have 2 tents if you need to veg and flower simultaneously.

I would not say one way is better or worse just that each will have its advantages and disadvantages.
Personally I run 3 tents in one lung room but environmental control has nothing to do with why I do that. For me it's about risk mitigation and life cycle control.