Is it safe? If it’s releasing carbon monoxide into your home and can’t be fixed, well, that’s a clincher. You will need a new one.
How old is it? If you don’t know, look for a date of manufacture on the unit. If there isn’t one, call the manufacturer with the model and serial number. You may need to turn off the heater and let it cool down before you look for this information. The average lifetime of a furnace that has been well-maintained is 20 to 25 years. However, it’s more about how well your heater is working rather than how old it is.
How efficient is it? This is called the AFUE (annual fuel utilization efficiency) and is a key factor to your final decision. The minimum AFUE requirement is 78% for electric furnaces and 80% for gas furnaces. If yours isn’t running anywhere near that, you could save money by replacing it. New models are anywhere from 80% to 95% efficient.
You might be able to lessen the workload of your old one with some low-cost fixes in your home like replacing weatherstrippping, sealing off leaks in the ductwork, or adding insulation. Have a professional energy auditor check your home for all the places where you are losing energy. You can also talk to the manufacturing company of your furnace and find out if there is anything that can improve its performance, like a new part instead of a completely new unit.
Is this a repeat problem? If you have had this furnace a long time and it keeps breaking down, it may be time to just get a new one. Your repair bills are likely costing you more than a replacement would.
Which solution will save you more money in the long run? Although buying a new one may cost more now, it may save you money in the end if it is going to be more efficient than your repaired furnace. Do a little math and figure it out. Take the difference of the efficiency of your furnace and that of a new one and multiply that percentage against your energy bills for last year. This will give you an estimate of how soon you can expect to receive your investment back. Did you know that a new, more energy-efficient model can also get you a tax break of a few hundred dollars?
If the first repairman or inspector says to replace the furnace, remember to get 2 or 3 estimates before you decide. Now that you know what to look for, you also know what to ask them. Even if your old furnace has a few more years left on it, you may decide you want a new one for convenience features like a programmable thermostat.