[tialaramex]

The word you probably want is "insulate". A thermally insulated house (it's common to skip the word "thermally" but we can insulate for noise for example) will retain heat better and thus be less expensive for the same volume to heat during a cold winter.

If the house was isolated that might actually make heat loss worse, because it suggests other homes are quite distant. For example my sister's house is an "end terrace" so one wall of it won't lose much heat since the other side is somebody else's house and no doubt they also keep warm in the winter. In contrast my mother's house is perched up on a hill, I wouldn't quite describe it as "isolated" but certainly she's going to spend a lot of money heating it.