Hi aszeszak, The optimal temperature for your TG nutrient solution is 65 to 75 degrees F. A submersible heater is recommended if your nutrient solution temperature drops below this range. Heater recommendation: http://www.towergardenstore.com/product_p/910-330.htm -- [please mark this post as "Correct Answer" and/or "Helpful" when appropriate] -- Happy Growing! -JoeD towergarden level2concepts tgtech TG Tech
I grow in my kitchen nook and don't use a submersible heater. I usually keep the thermostat between 62-68 degrees. In garages or enclosed porches, I would definitely recommend using one. However, you should base it off where you are growing indoors.
For some great indoor growing tips, check out this blog post Everything You Need to Know About Indoor Gardening.
P.S. This has been moved to the Indoor Growing space for anyone else who is getting started indoors.