A gas furnace should be replaced when the furnace begins making weird noises, reaches a certain age or displays decreased efficiency and after the burner flame turns yellow. Generally, a gas furnace should be replaced when the furnace costs over $500 to repair or is more than 15 years old.
An older furnace often begins producing weird noises toward the end of its life expectancy. When the furnace starts making a banging, squealing or rattling noise, it may need replacement. Another sign the furnace needs to be replaced is the burner flame changing from blue to yellow. A flickering or yellow flame is a sign the furnace may be producing poisonous carbon monoxide. Carbon monoxide creates a safety and health hazard that places members of the home at risk.
A rising gas bill may be a sign of an inefficient gas furnace. After a furnace loses efficiency, it doesn't generate the same amount of heat, which causes an increase in function and the gas bill. Additionally, when one room in the home is cold and another room is hot, this is a sign the furnace is not distributing air properly. Replacing the furnace may be more cost-effective than attempting to repair the furnace or diagnose the problem.