quik question on heat

i'm setting up a couple tents, but i have an issue with temperature.....its frikken cold 3/4 of the year where i need to set them up. i dont really want to use traditional heater(s) if i can avoid it.
i was wondering if anyone had any experience with root heaters for hydro? im going with soil, nothing against hydro its just what im used to, maybe ill switch at some point if can get a back up gen for my house. for now its all dirt.
i would like to know if anyone has used them for ambient heat or if they are even capable of that. the tents are both 4 x 4 and im going to be using led lights. the lights generate a little heat until they shut off and the temp drops pretty fast.
the veg tent might be ok but the flower tent will definitely suffer. i just need heat at low wattage so i can keep my bill down and not set off a usage spike the power co. might take an unhealthy interest in. i'd rather err on the side of paranoia then become a statistic. i searched around for anyone else asking that and didnt find much. if anyone has ideas i'd appreciate it.

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!

hmmm, i may be able to get something like that to work. i'll have to look into the costs on thermostats. set up right i could get by with one inline fan provided that the tent with heat is also the only means of intake and exhaust with backdraft dampers. hmmm
thanks thats got me thinking!