Consider two choices for the furnace to heat a building: an ordinary gas furnace with efficiency75% (seasonal average), costing $1000, and a condensing furnace with efficiency 95% (seasonal average), costing

$1800. Suppose the annual heating load is 100 MBtu (105.5 GJ) and the fuel price $7.00 per MBtu ($6.64 per GJ). Calculate the payback time for the second furnace relative to the first. Is it a good investment, if both furnaces can be expected to last 15 yr? (15 points)

Fig: 1