That's a question that every homeowner eventually asks, usually after another repair bill.
So how old is too old for a furnace?
On average a furnace that burns natural gas will last anywhere from 15-30 years depending on how well it's maintained. If you have neglected annual maintenance to save a few dollars, you will probably end up spending that money and more by replacing the furnace before you normally would have had to. An electric furnace will last about 20 years, with the same maintenance rule of thumb applying.
So let's say that your furnace is in need of major repair. Factors to consider are the price of repair, the cost of a new furnace and the life expectancy of the furnace you have. Many people will decide to buy a major appliance if the cost of repair is 50 percent or more of a new unit. If your furnace is 15 years old and well maintained, it could work for another ten years. If you haven't been faithful with regular maintenance the remaining lifespan may not be as long.
Since a new standard furnace starts around $2000 and varies depending on the size of your house it would make sense to buy a new one if the repair bill was approaching $1000.
In general, a furnace should be repaired if it is less than ten years old with a repair bill of less than $500
Another thing to think about is whether to replace your older furnace with a high-efficiency model. The average cost is around $4500. That seems like a lot, but if your furnace lasts 15 years, the increased cost comes out to about $11 dollars a month. If you have proper insulation and a furnace large enough to heat your space without overworking, the savings on electricity and natural gas with a high-efficiency unit should easily exceed $11 dollars a month. That means that your larger initial investment will more than pay for itself over time. If your furnace lasts 20 years, the extra cost per month drops to only $8.
Even if your furnace is working fine, there are some signs to look for so that a huge repair or replacement bill doesn't sneak up on you.
1. A rise in utility costs: This means that the furnace is operating less efficiently and is using more fuel to get the same amount of generated heat. This will only get worse over time.
2, Repairs in the last two years: Repairs become common in the last two years in the life of a furnace. If you are making regular repairs, it may be time to bite the bullet and replace it.
3. Strange noises: Rattles, bangs or the blower turning on and off too frequently are signs of impending furnace death.
Finally, older furnaces are more at risk to generate carbon monoxide as they age. A cracked heat exchanger, for example, can allow carbon monoxide to leak into your home. It's always a good idea to keep a carbon monoxide detector in your home, preferably near the furnace.