A furnace may need a tune-up if the furnace makes no heat or uneven heat, makes squeaking noises or produces a prominent smell of natural gas. Another big indicator is an increase in electricity consumption.
If the furnace is failing to produce heat, there is a good chance it needs to be serviced. In order to prevent an emergency situation, it is preferable to test the output of the furnace prior to the cold season. Uneven heat is typically caused by air leaks in the duct system. A tune up allows maintenance technicians to identify these leaks and repair them.
Furnaces are composed of a variety of moving parts, and these parts require proper lubrication. Failure to replenish this lubrication can lead to squeaking noises. If any of these noises are being produced by a furnace, it is a good indicator that it is overdue for a furnace tune up.
Smelling natural gas is a dangerous indicator of a problem. It is best to call 9-1-1 when this smell permeates the air. Immediately evacuate the premises, and be sure to leave doors open. A failing furnace may not be appropriately burning the gas and can lead to the home becoming filled with a dangerous amount of gas.