You may need 10w per sq. ft. to achieve room temperature for an insulated house. 5w per may prevent freezing in an insulated well house.
we can get an idea of your winter temps. You also may want to know your Outside Design Temperature which for my area @ 39 N. Lat. is +14F.
If you don't want to gamble $100, wire up a few 100w bulbs to a t'stat and see how many it takes to give enough heat.
In a medium size house, the center can be at 45F and the pipes in the walls can be freezing.
It comes down to a lump sum for insulation plus a small electric bill or you paying a larger annuity to the PoCo. If the payback period is less than 10 years, insulate.