Cold weather ventilation

[I respect women]

How much CO2 do plants actualy consume? I've moved to a stupid cold area and any fresh air that comes in has to be heated. A window fan and thermostat keep a large lung room 68-70 but last night it went 8 hours without kicking on.
3000w hps flowering and 1200w for moms/veg. It's not an easy room to seal and trying to avoid that if possible.
Most houses are in the 600-1000 ppm range in the winter but no idea how fast the plants would deplete that. Any ventilation info I can find is temp related and that not my issue. It hit -15C last night but there is 3 months of -30-40 coming very soon and shipping anything here is slow so I should probably get on this a week ago.
Any help is appreciated.

 

[f-e]

90% of your plant is made from air and light.

You know what you have to do. Save energy and improve the grow with better environmental control.

I once heard 4 hours, but it's such a variable it can't be believed. It's also surprising how much air exchange an apparently sealed room can have. A room in a house with a closed door, still gets a full exchange in a few hours. People don't suffocate in their homes very often. Poly-tunnels are often closed all day. I do something similar with polythene indoors, to get up humidity. Dividing the room between plants and lights. I think you would have to really try hard to damage one, but retarding them a little could be possible.

 

[I respect women]

What I'm looking for is some sort of formula that could calculate CO2 consumptoin by water use, plant biomass... or any other method.
I know there are endless variables that would effect it but just looking for a rough estimate. The propane stove and 2 people each producing 2.5 lbs a day should carry a lot of plants.