The user manual for a Lennox furnace recommends an annual service visit by a licensed professional service technician before the beginning of the heating season. If the system also contains an air conditioning unit, a second service visit before the beginning of the cooling season is recommended as well.
Regular service visits for a furnace keep it operating at its intended level of performance and efficiency. These visits can also extend the operating life of the furnace and prevent more costly problems from occurring. An inspection of the furnace's venting system is a part of the visit as well, which ensures that the carbon monoxide and other by-products of combustion are being exhausted properly.