As of 2015, the two types of fuel that are used in the Lennox range of boiler products are gas and oil. Gas is used in both the Lennox water boiler and the steam boiler, while oil is used as fuel to fire up water boilers.
The six residential boiler models offered by Lennox have annual fuel utilization efficiency ratings that range between 82.7 and 95 AFUE. The more energy-efficient models are also generally more expensive, with price range shown as dollar signs on the Lennox website. The most efficient boiler model sold by Lennox is the GWM-IE boiler, which uses a gas-modulating condensing water boiler.