Your overall boiler installation cost is directly proportional to the size of your house, particularly if it’s a full installation. The more rooms you have to heat, the more radiators and pipe-work you will need, as well as a larger tank. You boiler will also have to be big enough to heat enough water and create enough heat to cope with demand. It’s also worth factoring in any extension plans you may have for the house, and to be sure your boiler system will be able to cope with having to heat any additional rooms. This will prevent you having to upgrade your boiler again at a later date.