Whether at home or in a commercial facility, the indicators of a failing furnace demand immediate attention. A sudden, unexplained increase in your utility bills is a primary warning sign, as the unit struggles to maintain temperature, consuming more fuel. You may also notice inconsistent heating, with cold spots appearing in certain rooms or zones. Frequent and increasingly costly repairs are another red flag; investing more money into an aging system yields diminishing returns. An older system, typically over 15-20 years, will lack modern efficiency standards and may pose safety risks, including carbon monoxide leaks. Loud bangs, rattles, or persistent humming also signal mechanical failure. Ignoring these signs can lead to complete system failure, resulting in costly emergency downtime and significant discomfort.