Reply #4: You might try the incense test.

[safeinOhio]

On a really windy day light up a stick and go around the inside walls, windows and doors. You'll be able to see where the air is leaking as the smoke drifts side ways. Caulk and plastic around the bad spots. Sweeps on the bottom of doors and some insulation around the foundation might be a big help. In your case a energy audit could pay for itself in a few months.
I was real lucky when I bought this house. About 10 years ago the owner remodeled and did a first class job on insulating this old gal. I have natural gas too.
You have to be careful shutting off rooms in the winter. Big temp changes are terrible on homes.
Come on spring.