Sorry I don't know for sure but the only way to find out would be to put a thermometer underneath and see if it keeps the area warm. Hopefully someone that has more experience with these will chime in.
Edited to say. I found this link here that may help some. I guess my idea with thermometer won't work.
The product information says to use it with ambient temperatures above 50F. So no, I wouldn't use it in winter unless you are putting it in a heated garage or your house.