Do you have a broken furnace? Is your heating system less efficient than you'd like ... or perhaps not working at all? (Brr!) You have an important -- and potentially expensive decision -- to make. Should you repair or replace your broken furnace?

Sometimes spending money (on a new, high-quality furnace) can end up saving you money (on winter utility bills). But beware: An inefficient furnace does not always need to be replaced, because there are some fixes and maintenance that might solve the problem. For example, changing your furnace filters helps your system run more efficiently, as can making sure your humidifier is set to the proper level. Often, simple repairs like replacing the pilot light with an electronic ignition or sealing the joints in your ductwork may end up doing the trick.

If you really do suspect that you need a new heating or cooling system, the first step is to contact a reliable HVAC contractor to come and check it out for you. Remember, a furnace should last for about 25 years if properly maintained. So unless yours has been improperly installed, damaged or has faulty wiring, you should get many good years of use. How will you know when it's really time to replace the furnace?

There are 4 main reasons why you would need furnace repair services.

1) The Cost of Repair is not Worth it.

When a broken furnace turns out to need major, costly repairs, it is important to decide whether you might be better off putting your money towards purchasing a replacement, instead.

2) Your Present Furnace is Extremely Old and Inefficient.

If you move into a home that was built in the 1960s or even earlier, chances are that it has an old boiler system or furnace. This doesn't necessarily mean that you need a new furnace, but chances are that your system will need an overhaul to make it energy efficient for you.

3) The Cost of Running Your Furnace is Excessive.

Fuel to operate your HVAC system is often a major part of your household budget. If your energy bill is sky-high, you might want to switch to a less expensive power source -- from gas to electricity or vice versa, especially if you already have an old or broken furnace.

4) The Heating Load is Inadequate.

Heating load is the amount of energy required to maintain a steady 65-degree temperature indoors. To find out your heating load, you may want  to perform an energy audit, which will help you figure out ways to make your home more energy efficient -- and possibly save you from replacing the entire furnace. If you find that despite your efforts, your heating continues to work inefficiently, you probably need a new furnace.

Do the Math

If you replace your furnace with a 97% efficient system (look for an Energy Star furnace or A/C system and compare the AFUE and BTU levels), then you could cut your heating bills by approximately 20%. To see if it's worth spending the money, add up your fuel bills for last winter, then multiply that sum by 20%. Divide that figure into the cost of buying and installing the new system, about $3,000 or so, and you'll see how many years it will take to recoup your investment.

Updated November 19, 2018.