How cold does the house get in winter? If your ambient room temperature does not fall below 72 at any time then I would not bother with a heater. It is very difficult to keep octopuses away from heaters and they have no concept of anything so hot as to burn them (something Jacques Cousteau noted in his filming with live torches). If you need to heat the water in the winter my best (but not cheap) suggestion would be to use an inline heater (
something like this) on your filter tubing. Having never used one, I am not sure if placing it on the input or output side is best for the filtration pump but would think the more gradual temperature increase achieved by putting it before the filter would be better for the animal.