this post was submitted on 25 Mar 2026
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The furnace in my house dates to 1987. It just survived another cold winter. My plumber says a new one would use about half as much gas and that parts are no longer available for the old one. I wish I knew whether to believe him or not.
Gas furnaces from 1987 when new could convert 75-80% of the chemical energy in gas into heat within your house. They lose some efficiency over time, but not that much - I would expect it's still getting 70-75% of the chemical energy converted into heat within your house.
The maximum efficiency available today is around 96% on the same metric. If you need 100 units of heat today, you are burning 133-143 units of gas. With the best possible furnace efficiency today, you would only need to burn 104 units of gas, which is 22-28% less - certainly not "about half".
There are multiple special requirements for the best possible efficiency, and they are more expensive, both to purchase and to install. You might be able to save money on bills, depending on gas rates in your area, and the total cost to purchase and install a high efficiency furnace. I can't really answer that without a lot more information.
As for parts availability, there should be a model number and a manufacturer indicated on it somewhere. These days, most things service professionals have access to are also listed on the internet for sale. That one is easier to convincingly check.
Yeah, I'm inclined to think parts are available but my plumber would never bother looking for them. The guy I was going to rent the house to said he had tons of spare parts for my kind of furnaces and I was prepared to give him a break on rent if he kept it going. Unfortunately I didn't get the house renovated in time for him to move in (and I'm still not done) so I can't really expect him to do anything for me.
Is the heat exchanger still intact? No cracks? If it's cracked get rid of it before the carbon monoxide gets you. We went with a heat pump and will not return to a gas furnace.
No cracks in the heat exchanger. I have a CO detector mounted right by it in the basement (for whatever that's worth).
Newer ones can be a lot more efficient, but the high efficiency ones aren't just drop-in replacements either because they require additional piping to the outdoors which can be a big issue depending on where in your house the furnace is located.
Ask another HVAC company about your options and benefits... See if they say similar things... Most likely given that it's almost 40 years old vs The efficiency improvements are probably across the board on new models... And see if the numbers match
Don't trust the HVAC guy, you know, who wants to sell more HVAC
But do trust another random HVAC guy who wants to, in fact, sell more HVAC
???
Bruh everyone wants to make money selling you shit. They only person who will want you to buy nothing is you.
I get where you're coming from, but it's kinda isolationist and sad. Distrust profit motive, but try to trust people when you can. I don't want to make money selling this guy shit, for one :)
I can see how it could come off like that. I mean I generally trust the HVAC man's opinion on everything except whether I should buy HVAC services.
Personally I advocate for self-education. It might have been difficult to discover the refrigeration cycle, and invent the furnace but it won't take you more than a few hours to learn enough to check your own equipment. Or how to check the brakes on your car. How to find a leak.
It's quite liberating to be able to tell that they're full of shit. That isn't your Car's Air filter, or that your AC needs a capacitor not a $15,000 full replacement but that you'll be buying it from someone else.
Knowledge is power ✊