If you are planning on flowering with CO2, how do you plan on raising temps with T5 HO lamps? Are you going to use a space heater and a dehumidifier to do the job?
Because if so, you pretty much defeated the purpose of T5 HO lamps in that all the electricity it will take to dehumidify the grow space, AND THEN heat up the air that the dehumidifier just got done cooling down will be quite a bit more than if you were to just use a HPS or MH which will heat and dehumidify your grow space for you.
The nice thing about HPS and MH and CO2 is that they work symbiotically together.
It's the same thing with LEDs. They don't heat up your canopy enough to induce proper respiratory action which prevents the plants from drawing up nutes and therefore stops growth. Ya pretty much gotta HEAT your grow room if you use LEDs or T5's with CO2.
Now your other option a CO2 generator because those burn propane or natural gas to produce your CO2, therefore you might be able to somehow use the waste heat from that to warm up your grow room. *DISCLAIMER* If the waste heat from a CO2 generator is meant to be vented outside because of CO emissions do not follow this advice. I have never used a CO2 generator before and am unaware at how they operate.
My suggestion if you are still going to use T5's for flowering is not to bother with CO2. I'm getting outstanding veg plants with the colored T5's which in turn is setting up my plants with strong stems, tight internodes, large fan leaves, healthy root base, all in a nice coco/perlite medium. I then use a combination of MH, T5's, and Leds to flower. Everything has always turned out rock hard, sticky as superglue, and tastier than koolade.
CO2 is nice, last year I harvested 14 dry ounces off of one plant. Yeah the plant was a 4 foot tree, but it grew in a 1 gallon bucket! Needless to say the roots got so thick I had to break the bucket just to get the plant out at harvest time. The root system got so dense it stopped draining water well and got a little root rot in one area.
CO2 can be a bit tricky if you don't have the other variables dialed in correctly. And if you don't, the CO2 will just float around the room and do nothing. Now if you live in an extremely hot environment already, more power to you. Make sure to keep your root zone cool when your room temps are above 90F!