Yeah that will affect it. Are all your walls plastered (like no exposed stone)? Heavy window treatments and keeping doors closed helps. If you have a kitchen addition on the back of the house without a door, hang a curtain between it and the rest of the house (this can be applied to any additions or sunporches). Some folks go the extra mile and do that by their front door if they don't have a vestibule. We do not because the sun hits the front of our house for a decent part of the day.

Granted, I live mid-row in a much smaller house(896 sq ft), but just hanging a curtain between the kitchen addition and the rest of the house helps - our kitchen can be COLD. The bill I'll be paying this month is $90, 24% lower than last year's (it's been so warm!). My summer PGW is around $45 (gas stove).