I hate to be a budinski, but this thread has the most info I have found so far on this matter and it didn't make sense to start a whole new thread for just a question or two.
I bought a four foot fixture and two T12 3100k bulbs for the 6'x3' enclosed greenhouse portion of Odin's indoor enclosure that we are planning, (his MVB and CHE will be in another attached but separate area). Do you think they will have sufficient light output for growing his plants in there full time and do you have any idea how much heat they will produce?
The bulbs will produce a little heat, but the ballast will produce a lot more. Is the ballast built into the fixture or is it a separate entity on the cord somewhere?
You will have to run it and see what it does to your temps. Too many variables to predict it.
Same with the plants. Two 48" bulbs in a 6' enclosure should make a pretty good amount of light, but I don't know if that will be enough, or the best spectrum for plant growth. Maybe it will be. Try it.