A community hall is fitted with a large gas powered non-condensing boiler, housed in the basement, which supplies hot water for a kitchen, and heating via a radiator system. The boiler is quite old, having been installed in 1976, efficiency being quite low. The building is used seven days a week, and typically for nine hours per day. The gas bill is currently high and a quote has been received to install a condensing boiler, with an increased efficiency. Assuming the heating and hot water requirements will not change, and based on the savings made in gas consumption, what is most basic estimate of the payback period for the new boiler (years)?

Current annual gas bill = 4000

Cost of new boiler = 6000 Existing boiler efficiency = 40% New boiler efficiency = 80%