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Lennox makes gas and oil furnaces. For each of these types, it sells a few different categories of furnace, stratified by price and efficiency. Energy efficiency is described in terms of Annual Fuel Utilization Efficiency (AFUE), which describes what percentage of the energy in fuel is converted into thermal energy for the house.
Lennox's gas furnaces range in efficiency from 80% AFUE to more than 98% AFUE. Efficiency does not directly correlate with price; there are furnaces with 80% efficiency in all three furnace categories.
The Merit Series of furnaces is the least expensive. Of these, the G40 is the most basic unit (with 80% AFUE). The ML193 is similarly basic, but does boast somewhat higher efficiency (93% AFUE), due to the separation of the blower compartment.
Within the more expensive Elite series, the G50 (single-stage), G60 (two stage) and G60V (two-stage, variable-speed electric motor) are relatively inefficient (80% AFUE). These models use extra insulation, and consequently produce less noise. They also use somewhat more durable materials. The G60 has two operational stages, which allows it to operate at a lower speed most of the time.
The G51, G61, G61V, and G71P have higher efficiencies (92%, 95%, 95% AFUE, respectively). They run more quietly than other models because of special insulation. The materials are also better, and the heat exchangers for these models are guaranteed to last longer.
The two Dave Lennox Signature furnaces are the most expensive. The SL280V has an AFUE of only 80%, but its fan has the capacity to help cool a house during the summer. This model is also billed as especially quiet.
The top-of-the-line model is the SLP98V and has the extraordinary AFUE of 98.2%. This efficiency is due to various features, including a heat exchanger to capture excess heat, the ability to draw from multiple fuel sources, and compatibility with an advanced digital thermostat.
There are fewer models of oil furnaces.
The O23 and O25 both have intermediate prices and efficiency (83% AFUE). These are basic models without many features.
The O23V is more expensive but is just as efficient as the other two. It does have better insulation and runs more quietly. It also operates at variable speeds, which means that on days with less heating to be done it produces less noise and saves energy. The O23V also has a humidity control feature.
O23 and O23V use Beckett burners; O25 uses a Riello burner.
Care and Maintenance
Lennox recommends having both gas and oil furnaces checked by a certified technician on a yearly basis.
The furnaces are covered by warranties lasting a minimum of five years. Heat exchanger components typically fall under a longer warranty ranging from twenty years to the whole lifetime. The five-year parts warranty can be extended to ten years for an additional fee.