We have just installed a new boiler in our house. It has cost £4700 to install, but it will last for 9 years before it needs replacing. Nevertheless, the supplier assures us that it will cut our heating costs by 30%. This is good news as we currently pay, on average, £500 every quarter year. The supplier insists that it will pay for itself (i.e. save enough money to cover the cost of the purchase, before it needs replacing).