A homeowner in Cary, IL in McHenry County replaced a Lennox gas furnace about 15 years old with a Lennox dual-fuel system: an EL297 gas furnace paired with an EL18KSLV 3-ton heat pump, a cased coil, an S40 thermostat, a media air cleaner and a power humidifier. Our crew ran new 2-inch PVC venting for the furnace and completed the work in October. See our Lennox work in McHenry County. Tip: if you have a dual-fuel system, ask your installer how the changeover between the heat pump and the furnace works.