My house is over 100 years old too, so insulation is pretty much non existent.If you believe it could have been an issue I suggest getting a c02 monitor.
I've exhausted into the same room but my house is over 100 years old.
Any reason the quality couldn't be related to the genetics?
The genetics I grew, were one Fastbud and one Mephisto, too different quality breeders.
My suspicion is it was the nutrients, as it's not looking like a co2 issue.
The nutrients were new to me, the Fastbuds was definitely locked out and suffered in flowering, but still got 2.6 oz of crap weed.
The Mephisto is a touch better, I get a little buzz from it, that doesn't last long, much worse than street bought weed sadly.
I got 6 oz from the Mephisto plant.
She grew well until towards then end of flowering she lost most of her leaves and loads of trichomes, not sure what caused this.