If you know you have a gas furnace in the basement, but can't distinguish it from other generic metal cabinets or stacks of boxes due to your intellectual temperment or lack of diy enthusiasm, get it checked yearly. Friends of mine had one blow up in their basement from neglect. Likely a rare occurrance, but gas or lpg can be dangerous. ...
For those w/o the knowledge, this safety angle might be good advice. Though, as someone mentioned earlier, it is only a snapshot, and may not tell us much/anything about the safety over the following season. I suppose it might catch something that came up the previous season, so the exposure might be limited if the safety issue didn't already create a problem. More later....
I guess my "evidence" that routine maintenance is worth it is that in 28 years of living in MN my furnace has never malfunctioned in a critical time. Nor has my furnace guy ever--never once--recommended replacing anything or doing some other, higher level work that didn't need to be done. So I trust him, and it is well worth maintaining the relationship with him, just like having a good auto mechanic. ...
Well, maybe. Kind of like people who say their FA is doing a great job, if you aren't knowledgeable about furnaces/finances, how can you know your guy is doing things right? Does he provide a checklist, what he tests and what the results were? If so, that might be enlightening.
I know you put "evidence" in quotes, so yes, this is not really evidence. Back to that 'snap shot comment' - When I think back to the furnace failures I've had - not one of them would have been detected
before the failure:
A) Motor bearings shot - started squeaking mid-season. I was able to get it apart and get some oil onto the 'permanent' oil wicks, and get through the season - replaced it the next year. ~ $100 and a few hours work.
B) Gas Valve - This just went bad. When I went to start up the furnace, pilot would not stay lit. Worked one day, not the next. There was nothing one could do to foresee this, it is a sealed unit. Replaced it. ~ $100 and a few hours work.
C) Draft inducer fan squeaking/sticking - Worked fine at the start of the season. Mid-season started slowing/sticking. I was able to get some oil in the bearings and it was fine. These things aren't really meant to be oiled, so it's a little tricky to get it in the bearings. This year, since I had things apart for the gas valve, I removed it and worked oil into the bearings as a preventative. Essentially $0 - a new one is ~ $200 on-line, I assume a furnace guy would mark that up and charge another $200 for labor. But again, not detectable by inspection.
D) Thermo-couple -
maybe - If you have a standing pilot (getting rare these days), these things do tend to age and burn down to a stump. So these could be replaced pro-actively. But they are cheap (~ $5) and are very easy to replace. I keep one on hand, so I'm not stuck when the stores are closed. Replaced one IIRC, and one that was OK when I was trouble-shooting the gas valve.
So regarding safety - even if you are not a DIY or tech type, I think it is good to get familiar with how the furnace operates when it is running properly. If you just watch it go through a cycle occasionally and look for problems, and be aware of how it should sound and run, I think you will do more for your safety than an annual check up.
You are home all the time, that guy checks it one a year.
For mine, I know I am 'tuned in' to hear the draft inducer fan kick in, then the gas jets woooosh a few seconds later (when it detects a slight vacuum from the fan), then the blower comes on ~ 30 seconds later. After the set temperature is reached, the flame shuts off, and the blower stops about 30 seconds after that.
Every once in a while, just watch the flames start, and look for changes when the blower comes on, and watch it as it shuts down. If anything is abnormal, check with someone.
I have no direct evidence one way or the other, but I did have regular cleanings/tuneups for several years as my furnace was 20+ years old. Every time the service guy recommended a whole replacement, every year I declined, and every year he came up with a part or two that needed to be replaced for a couple hundred bucks. After being told parts were becoming hard to come by and would start getting more expensive, I stopped the annual cleanings/tuneups and just replaced the filters myself. Twelve years later and not a single problem. My furnace is pushing 40 years old and has run with less trouble since I stopped the annual tuneups.
I certainly do not want my furnace to blow up, but I also don't want "routine" maintenance that seems to damage parts or reduce their useful life, like turning off airflow and running the heat until the emergency cutoff kicks in.
I wonder what the heck he could be changing every year that cost $200? There aren't that many 'wear' parts on an old furnace! Pilot, gas valve, thermo-couple, motor, belts maybe, a couple safety switches and maybe a fan switch (the old ones sense HEX temperature, mine is time based). 'Funny' that it runs fine w/o those changes!
-ERD50