If you can get your tents close enough.. or back to back/side to side whatever.. You will then have 2 sets of lights running at alternating times right??? Run a venting loop from one tent to the other.. you would need 2 vents basically running in a circle with a ducting fan on each that sucks the air in a loop. Then you would need 2 thermostats.. one in each room.. so when the room gets cold.. it turns the fan on and pulls warm air in from the other room that has the lights on.. And voila.. you can heat the room that has the lights off.. with the heat from the lights in the other room that needs to be exhausted in most cases anyways ;-) This works really well with HO-Flourescent and LED lighting... HID is a little different story because they put off a TON of heat! but it can be done with the right equipment. Running 2 sets of ducting with 2 duct booster fans might run you about 50 bucks.. And its not going to cost hardly anything on you power bill to run those little fans.. The expensive part is going to be the thermostats.. but you could probably hook them up to a cheap timer that would do the trick also.. Hope this helps.. Good luck!