The time to replace an old furnace is before it creates an uncomfortable or unsafe situation for you and your family. Buying a new furnace is a major cost and one you should plan for in advance. If you put it off until your furnace fails completely, you could wake up some cold winter night facing sub-zero temperatures and a furnace that's not producing any heat.
A furnace that has been operating for 20 years or more has likely seen its average life expectancy. Although a well-maintained furnace can run for up to 25 years, some don't make it that long; others work for a few years longer. Keep in mind, too, that an older furnace likely has a lower minimum efficiency standard even if it is well maintained. But age shouldn't be the only factor to consider in deciding whether the time has come to replace your home's furnace. You need to be alert to other more obvious signs that your furnace is nearing its end.
Increased Utility Bills
Natural gas and electric bills that continue to rise could be signs your furnace isn't working as efficiently as it did in the past. The same goes for an aging oil boiler. As a furnace gets older, it has to burn more fuel and run longer to put out the same amount of heat. While maintaining your furnace and getting it serviced on a regular basis can extend its lifetime and save you money in heating bills, eventually, you will still need to replace it.
Frequent Furnace Repairs
When you find yourself making constant repairs to keep your furnace running, it's likely wearing out. Old furnaces break down because they have to work harder. As a result, frequent breakdowns occur as a furnace nears the end of its lifetime.
Pull out your checkbook to see how many times you've had to call a service technician in just the past year. If you don't like the numbers you see (including the repair costs), it may be time to go furnace shopping. The more problems you've had, the more likely your furnace is struggling to keep up with the demand placed on it.
Your furnace may be waning if repairs require more new furnace replacement parts to get it up and running again. It may help to compare the cost of making frequent repairs against the cost of investing in a new higher-efficiency and better-performing furnace.
Another sign that your furnace is outdated is if the repair technician has to order and wait for replacement parts. Furnace contractors don't usually keep an inventory of parts on hand they aren't likely to use often.
Rust and Soot
Rust inside your furnace or on the vent and flue pipes means the furnace is malfunctioning and may be leaking carbon monoxide from cracks in the heat exchanger. If your furnace is an oil-fired boiler, look for flaking and scaling rust on the outside of the boiler as well.
Black soot streaks on walls or around the furnace and heat registers are additional signs to watch for that your furnace has problems. Not only does soot signal a potential fire or carbon monoxide hazard, its presence generally means you are spending more money to heat your home. Soot is a sign of incomplete combustion; therefore, a fuel that isn't burning completely isn't producing as much heat.
If you have a gas furnace, a pilot light is an indication that it's an older model. Newer models have electronic spark or hot surface ignitions. Also, an old furnace often makes banging, squealing, and rattling noises. It's the furnace's way of telling you something isn't right. Other noises you hear that may indicate a problem include the blower fan in a forced-air furnace turning on and off frequently or running continuously, especially if there is no heat coming out.