If where you have the fish house for the winter is around 40'f, your not going to need a heater. UNLESS, you are planning on feeding them so that you can speed up their growth rate over winter. If thats the case, I suggest a reliable aquarium heater that is heavy duty (but affordable). One of my favorites is made by Hydrofarm and it is made out of titanium. Sound expensive...but you can pick up a 350 watt unit for $30! I would suggest that you keep the temp around 68'f to 70'f and I would also advise taht you use a reliable aquarium filter, like a Fluval as well as a biological additive, like Green Clean's Xtreme Bacteria. Also, get a cheap test kit (or have a local aquarium store) test your water to make sure everything is okay. Good Luck:-) Chris@AZPONDS