Unless your home is very new, you will lose some heat through draughts around doors and windows, gaps in the floor, or up the chimney if you have one.
Professional draught-proofing could cost around £200 for materials and installation for your whole house, but it could save you around £25 a year on energy bills.
Installing a chimney draught excluder could save an additional £17 a year, as well as 70kg of carbon dioxide emissions.