Wow... that stung...
No posts missing from this thread btw, I checked.

I wish I could say I was a sealed room expert but I've never done one yet. There will still be oxygen in there- remember plants actually generate O2 in one of the steps of photosynthesis. Their NET is co2 INTAKE and o2 OUTPUT. Most of the outside atmosphere is actually nitrogen, and the sealed room concept drops that to a lesser fraction of the total atmosphere. You're giving the plants N in their feed anyhow. I'm glad it's working out for you. One thing to save on gas is to put the lights on a separate circuit so that you don't exhaust the CO2 that you paid for along with the heat that you don't want.