I can't give you precise figures for your situation, but when I built my house in 2005 I put in underfloor heating, with a modern efficient boiler and timings set to suit my lifestyle (at home all day) - then the price of oil doubled practically overnight. When I left to move down here I was paying £150 a month for a well insulated bungalow with 4 double bedrooms, lounge, dining room, and family room with large bathroom and two ensuites.
Hope that helps