This depends on your usage. Is anyone home during the day, the average temperature outside as well as how hot you want to keep it inside.
Here is a suggestion, once you identify the home you are interested in you and your agent can call PSE&G and they can advise what the average cost for heat is per month. Not many people know that you can do this and this is public record.
Let me know if you need any assistance and I will be glad to help.
Terrie O'Connor Realtors