Why is Furnace Maintenance Important? | Ask This Old House
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- เผยแพร่เมื่อ 2 ก.พ. 2025
- In this video, This Old House plumbing and heating expert Richard Trethewey teaches host Kevin O’Connor about furnaces and why it’s important to maintain them properly.
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Kevin O’Connor gets a primer on furnace maintenance from plumbing and heating expert Richard Trethewey. Richard first explains to Kevin how a furnace works before explaining the different checkpoints that an HVAC technician would use to check the furnace. After that, Richard shows Kevin the dangerous conditions that can exist if the furnace isn’t serviced by a professional at least once a year.
Where to find it?
Richard emphasizes the importance of a yearly service call for furnaces and AC units and what to expect from technicians when they come.
Richard explains that a proper technician would check all the regular safety devices to make sure they work. That would at least include:
Safety device check - Richard explains what’s on the furnace and how to check them.
Next, Richard explains that they will do a combustion test with a combustion analyzer - this test measures how much fuel is going in and what are the emissions going out. It measures for temperature, carbon monoxide, carbon dioxide, and nitrogen oxides. This test is important because defective furnaces could literally kill you, either through carbon monoxide or through an explosion, and should be tested once a year.
Richard also points out that the air filters should be checked and replaced if necessary. This step should actually happen twice a year, so homeowners should be doing it six months after the service call on their own.
Richard tells Kevin that the last thing a technician should check is the AC coil. They’re just
looking to make sure it’s clean. If the filters are not getting changed regularly, some of that dirt and hair can end up on those little fine coils and prevent the air conditioning from working correctly.
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Why is Furnace Maintenance Important? | Ask This Old House
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In all my years having my furnace cleaned and serviced, I had never seen them checking combustion levels and such. They cleaned the areas with a vacuum and brush and lit the pilot light and that was it, which is why I stopped calling them and started doing it myself. Now, I don't have the tools to check those other levels, so I'll have to get someone to do that. But obviously, I'll have to ask for that specifically, because none of the companies hired ever did it on their own.
A lot can be done without test equipment. For instance, a cracked heat exchanger can be found by looking at the flames while the blower fan turns on. A cracked heat exchanger will blow exhaust air thru the cracks and the flames will get wavy like a wind blowing past them. An experienced tech will know by the color and shape of the flames, along with checking for soot between the burners and the exchanger opening the gas/air mix is within spec. The combustion analyzer can help dial in the gas for a couple percent more efficiency. But to your point, you don't know in the first place if your tech is a genius at reading the indicators of a potential issue.
Same here I had a guy show up, I have a fairly new furnace, he tested a few things like temp in duct work, spent all of 10 minutes (no kidding), cleaned a small rod. I felt he didn't do a good job or knew it was a new furnace so the service wasn't really needed. It's natural gas, and charged for $200 for basically looking at the unit, I was not impressed. So probably more needed for an older furnace. Waste of money in my case. I change the filters myself.
Same here. They don’t even own a manometer to set gas pressures or check static pressure. I stopped doing the contracts because I can clean the flame sensor and change the filters myself. I did install hi end CO detectors on all three floors. Too much filtration can create too much static pressure for the newer blower motors that have electronic controls?
@@rzh3443 I think that's a good strategy and would agree. What's the point of a fake service. I watched him so I can see what to do next time. If he did a real service, I have no issues hiring a pro but this guy did basically nothing for $200. He did reverse my filter around I had it the wrong way, so there was that, other than that, waste of time. Also depends on the tech I guess, this guy was a little off, maybe not skilled or properly trained. Might be worth hiring a pro in 3 years with a different company to see if my experience is any different. I am just going to use regular filters and change them out often, every 3 months or so, they really inexpensive.
@@westbccoast What happens is that they can check some parts, but leave and X time later it fails. I have dealt with three local companies- all the same. I think they do the "tune up" to see if they can gat some parts to replace ( 300 percent plus mark up). I wound up buying OEM parts on line for the most vulnerable parts ( flame sensor, inducer pressure switches and igniter) to have on hand. Ditto for AC ( contractor and start/run capacitor). As an example they quoted me $350 to come replace an inducer pressure switch. The OEM part on-line was $15 ( need only a nut driver to replace it). If you haven';t already watch the Word of Advice series on YT- He goes through the main processes and repair details.
So thankful for this old house as a new home owner this is alot better then paying $200 just so someone can show up
Phew wish i knew this months ago. Just bought the house & wanted the 7 yo furnace checked. Called a furnace company & their guy never went through the furnace like this. He kept saying that it was a fairly new furnace it was running fine. Hmm Thx for your great shows, videos & passing on the info.
Sounds like something you'd see on Inside Edition, where they catch repair people doing nothing but then charging a lot for it.
Richard, Tommy and the others have a level of knowledge and expertise that is extraordinary! We're fortunate to have their explanations and demonstrations to help us better understand plumbing, carpentry, electrical, etc.
Always have the tech show you the problem. Earlier today during a tune up, they told me my heat exchanger had a crack in it. They were professional enough to show me the crack.
I like how Kevin acts like he hasn't heard all of this before. Kevin knows all of this as Richard has explained this to him multiple times. But he always pretends like he is learning all of this for the first time.
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Story time! My Mom had a problem where she could NOT keep plants alive inside her home. She, unrelated to the plants called an HVAC guy who after doing some testing on her mid-70s furnace discovered that it was POURING CO into the house. After getting the furnace replaced she has had zero green thumb issues indoors! My man saved my Mom's life ❤❤
She should have a duel co/smoke alarm.
I think “pouring CO into the house “ is an overstatement. If that was true, she would have gotten very sick or died.
@@rodgraff1782yeah this story sounds, um, exaggerated let’s say.
If only they made CO detectors
This is complete nonsense and anyone with even a middle school science education would know. CO2 is not only not harmful to plants, it's essential for plant growth. They rely on it like we rely on oxygen. The idea that having lots of CO2 in one's house would hurt the house plants is simply retarded.
My central heat and air unit is over 35 years old. Recently, the temperature guage stopped controlling the temperature in the house except when other heating units like the oven or dryer were on. The temperature guage was replaced yesterday. Overnight the temperature dropped to uncomfortable levels. After about an hour after waking up the temperature has risen to a comfortable level. I feel the heat. Ichecking tge futnace worth a try or should I replace the unit?
Thank you for the video! Sharing with my real estate clients.
Important to note that this only applies to gas fired furnaces. Mini splits, heat pumps, and electric heat does not have this problem as long as you use the right filters, change your filters often, and clean your units regularly. There is no CO or NOx gas in a furnace that doesn't burn propane or natural gas.
Is that also true for oil furnaces which is what I have?
@BobbieJeanM No, Oil Furnaces should be serviced annually as well. The jets (sprays the oil into the burner, causing it to for tiny droplets that burn easier), filters, etc all need to be cleaned/replaced.
You still have to have the delicate inverter boards checked and inspected. They are very expensive to repair if the high voltage board goes and damage the other control boards and variable speed motors
Yes, better off going all-electric and then you can avoid plumbers altogether. Our last house had an electric furnace (cost, $700 vs $5,000 for a gas furnace), and an electric water heater ($275 vs $1,200). These prices are all CAD as I live in central Canada. The monthly bill was not much more, electric appliances last a lot longer than gas, and you can repair/replace any of it yourself for very cheap. Add some solar panels with your savings and knock your cost down even more.
@karlhungus545 No thank you! Electricity is ridiculous expensive here. I plan to go to a Tankless system eventually for Heat and Hot Water. Will save a ton on Gas and such, but also requires annual maintenance.
23 years on mine! Low humidity is a great thing for heat exchangers. Heat rise must be just right too, 40-70 degrees F. CO detectors too!
Does it matters if i have floor heating?
THANKS FOR THE INFO 😊❤
Amen…..same applies to literally every piece of equipment in a standard home.
beginning of winter would be a better time to share this advise
What about annual maintenance for a Gas Boiler furnace for Baseboard hot water heat? What maintenance needs to be done for those?!?
They need to be cleaned. Try youtube.I hear they make videos on how to do stuff..
@landonlandon5533 OH I know. My question was more to TOH and if they have a video or could do one for it. I just give mine a good vacuuming and such before starting it up for the season.
Cleaned and they need to be analyzed as well
steven lavimoniere is the youtuber to watch... he's up in MA.
@@thebluelunarmonkey I've watched him a few times.
I love to watch techs talk about the importance of furnace maintenance, my carrier furnace is 20 years old and besides changing the filter it has never been touched, it works flawlessly....😶🌫
Can you do a review on electric HVAC ?
This Old House: please do a video on Gutter Guards...which ones work, if any. Cost effectiveness etc.
Being in home repairs, I deeply believe that most if not all solid top gutter guards with the little lip is very near worthless.
I would recommend just the old fashioned open steel screen type.
Both Home Depot and Lowe's carry these. They also carry the new snap in one's without the hinges. I have used both with successfully. However, there seems to be pros and cons to just about anything including these. For example, the steel old fashioned type eventually rust (takes years) , they are not the best around pine trees due to pine needles landing in the holes, leaves can still get in on the ends, and in some applications don't look the best.
The newer style guards over lap pushing into a slot (you may have to do slight modifications including bending down the very ends - or custom cut a piece and then shape for the very ends. Moreover, sometimes the power coat can break down and rust in time.
Other folks I'm sure have their opinions and experiences as well., but these are mine.
Plus going this route doesn't break your bank account.
Hope this helps.
RB in Mid Georgia
I wound up buying leaf filter. It isn't cheap and purchasing it is like buying a new car. SO far, through several rain storms, it works, but their warranty has a lot of if ,buts and ands. I think TOH did do a review of these guards at their site. Depending on your age and the levels in your home , you may or may not want to bother because they all need some maintenance at some point despite the sales hype. Agree the solid type guards are really only effective for leaves. Tree seed and pine needles would be elusive captures.
I have been pleased with Gutter Glove since 2009
Out of curiosity, what’s a good price for an annual maintenance call for a furnace combined with an AC unit? Not asking about repairs…just the call for service and going through the checklist
I don't know. My honest guess would be a range of $125.00 to $175.00.max plus the filter.
Probably, in part too the area of the country.
When I did residential work before i left for commercial it depended on what needed done. Basic clean and check should take no more the 1 hour 15 mins. We were 105 for the check and any parts need with labor was extra.
Upstate Ny - 200-300 dollars for "tune up" both units. They do not do combustion tests or gas pressure adjustments for that. If you need parts or refrigerant that is extra big time.
@@rzh3443this is why i never have or will pay for annual maintenance in my furnace.
$69-$89 tune-ups are common in California
It would be really cool to see maintenance and checks that should be performed for heat pumps as well.
I have my furnace serviced once a year and my central serviced once a year and I change the filters on a regular basis -- monthly. Should this take care of the thorough inspection you showed on this video? One other question, what are your thoughts on replacing the gas furnace with electric furnace. I've heard this announcement twice.
Cracked exchanger a Lennox?
Pretty great
No need to scare homeowners into thinking a cracked heat exchanger will kill them. Yes it is dangerous, but 2 things. Heat exchangers in this application are under a negative pressure due to the draft motor that he mentioned, air would be getting sucked into the heat exchanger not pushed out. The furnace also has safeties that he also mentioned that will detect when the flame is blowing back into the cabinet due to air getting into the heat exchanger. But absolutely you should get your furnace and ac maintenanced twice a year, once for cooling season and once for heating season.
1. Good luck finding an HVAC tech who will actually do any of this testing. They are there to do one thing - sell you a new furnace.
2. Many HVAC pros believe it is paramount importance to have as much airflow as possible through the unit, because the more airflow is restricted by a filter, the harder the unit has to work. A filter is there to stop big things, not small dust particles.
3. Every home should have a combination fire alarm/carbon monoxide detector on every floor at minimum. An additional plug-in carbon monoxide detector as backup is a good idea as well. Carbon monoxide will kill you. Spend the few bucks.
Even I have HVAC inspections annually, if for nothing else than to geek out with the technicians.
Very wise. Best to have HVAC checked out for a few hundred vs costly HVAC replacement. Americans don’t seem to understand this though.
The problem is that almost all of the service companies are worthless and you're often better off NOT having them touch your furnace or air conditioner.
Thats bs and you know it, only a fool says this. Might as well say you never need to have a tech look at your vehicle during a repair, you will do it yourself by youtube videos.
There are a lot good companies out there, homeowners are not wanting to do basic research for a good contractor. Doesn't take much effort to check on a companies credibility.
@@zack9912000 You're obviously a repair man and I touched a nerve. Why don't you tell us how to identify a good contractor instead of posting a worthless rant.
@@zack9912000 Hahaha...I stopped getting plumbers to do those useless inspections on my furnace YEARS ago. This is our 6th house. I have a high efficient Heil furnace (came with the house, built 2012) here in Central Canada (-29C atm), so it gets used. The only maintenance that makes any difference is changing your filter regularly to make sure the motor doesn't run too fast, and cleaning the flame sensor every year. I can do those myself easily and save $150 per year. If contractors didn't gouge so hard, people might actually use them. I've even bought all of the parts that can fail on these (two motors and the computer board) so I don't get blackmailed by some scumbag plumber if the furnace goes in the dead of winter. My next build will be infloor heat, all electric, water heater too. Then I can fix anything myself (don't need a gas ticket), it's 1/5 the price of gas appliances, and it lasts a lot longer without needing replacement/repair.
@@zack9912000 You just proved his point -- everybody knows ████ well that when you take your car to a 'random' shop, they'll do anything from overfilling your oil (causing a smoking mess when your exhaust heats up), to over-torquing your lug nuts (causes broken studs), to mixing the wrong coolant in your radiator (becomes sludge and ruins engine), all the way to INTENTIONALLY breaking something, slicing something, loosening something, draining something, shorting something, or burning something.
It's just a fact that for regular MAINTENANCE, the average person IS better off watching a video on YT, instead of trusting a half-witted sociopath with their daily driver. Even if you have a furnace guy that you trust, paying someone else $100 an hour to change a filter is simply not prudent.
@@karlhungus545 That's a great, logical approach, and in the worst case scenario, you can have a backup space heater.
In gas furnaces, is it customary that new air goes in from the bottom of it?
I think that is how most are done these days, though my old system pushes air in from the top. The AC unit is actually beneath the furnace stuff on mine.
Yes it’ll come in from the blower motor at the bottom why having a clean filter is important
Your model number will indicate if it is a cross flow (horizontal mounting) or upflow or downflow. Some can be installed in multi directions after reattaching some parts to the new orientation
Had an older neighbor whose daughter had given her phone number 25 years ago in case anything was going on. Her outdoor heating unit hadn't been serviced in years and hers was causing fumes of natural gas to affect my house, she had the repairman out the next day and he told me how bad it really was. These things have to be serviced, it's not a wood stove and even with those the chimney will have to be serviced. These things escape older people's minds, especially older women who haven't had to deal with such things in their lives.
Great video: Its better to have someone show up once a year or once every two years for several hundred dollars vs you HVAC stop working and your out 12-15k.
Can you provide the checklist shown in the video? Or where can i find it? Google ai? Lol
I would love to see HOW to clean the A/C fins. I had an electric furnace installed and they only told me after they had sealed everything back up that the existing ac fins were dirty and that I should hire someone to peel the furnace apart to clean them.
You uninstall the coil, recover the refrigerant. Temporarily Braze the lines closed on the coil to keep the water out and rinse the coil out with water outside. That is really the only way to do it right. Doing it in place with cans of coul cleaner doesn't work as well.
The whole problem now days is these companys just want to make money by selling you a new furnace. The service men get commission for selling you a new one so you need to be really careful when they come to inspect it. It is sad how companys are now. If a company comes in and says you need a new furnace that is 5 or 10 years old get a second or third opinion. Also if you find out a company has tried to scam you report them. It is a great idea to get them checked annually in theory but a lot of scamming .
Everyone tells you to replace drafty windows and doors but I’ll keep mine as it will keep CO levels down from my 50 year old furnace tyvm.
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You can have too much filtration.
This "how to" boiled down to "call a pro."
As a retired first responder for a gas utility I can tell you, Richard does make a lot of good points but he is totally wrong about cracks in the heat exchanger putting carbon monoxide (CO )into the airstream; yes, cracks can contribute to products of combustion entering the airstream but not in the way you think. Once the blower comes on it puts positive pressure on the heat exchanger and if the cracks are large enough this will cause flame rollout to enter the vestibule of the furnace causing products of the combustion or CO to enter the area around the outside of the furnace and possibly get sucked in through the blower compartment. The furnace Richard was showing had something called flame rollout switches that would prevent serious flame rollouts from occurring by locking out the furnace , they’re not perfect, but in most cases they work as designed preventing hazardous conditions. Just a note and reminder this is the 21st century everyone should have a carbon monoxide detector /combustible gas detector & smoke detector (nowadays they have all three combined into one ).
Stay safe out there , have those furnaces periodically cleaned /serviced and make sure you have those working detectors 👍.
P.S. , note to this old house producers: videos like this should be done in the beginning of the heating season (October ) not at the end of the heating season (March almost the beginning of April). I’m assuming you’re going to talk about maintaining air conditioning systems in December? Come on guys, let’s use a little common sense.
The main problem is the HVAC industry has a very shady reputation. Most homeowners are reluctant to call someone out for fear of being taken advantage of. It’s very off-putting to hear boogy man stories and easier to take the “if aint broke dont fix it” attitude.
What industry doesn’t have a shady reputation?
I think it would be a good idea to get furnaces checked every other year but the problem is these yearly checks are a great way to come into your home look at the furnace real quick and say you need a new furnace. It is a great way to make money for these companys. It is sad but now these service men get commission to sell you a new furnace so be carefull.
Uh Oh GAS. My cousin is building a new house in California, they were told they cannot put in any gas appliances or wood stoves.
That's what socialism looks like, folks. You get what you vote for lol
Come on over to Pennsylvania, still using coal 😅
Because Newsom and his buddies own stock in the electric company and other green energy crap. They are forcing the people to do business with companies they have interest in, follow the money.
@@dladd10 Or go to Florida. That's where you'll now get a rebate to cover the tax on new gas stove purchases. All meant to 'own the libs' by Guv Ron who has taken millions from other programs to fund it. The plot twist? Over 95% of Floridians don't care about gas stoves because theirs are ELECTRIC.
@@shanew7361 you have absolutely no idea what socialism is if you think that’s is socialism. 🙄
One guy giving basic info while the other guy pretends not knowing anything. Seems like a theme lately.
Furnace maintenance is a joke. It's there for sales for the company.
OMG! Gas and oil furnaces………
nobody has $20,000 to spend on an electric system...
“How dare they!” -Greta
@ronald woofer Let alone our electric grids are antiquated trash and often fail lol Plus to produce electricity is worse for the environment lol
my reactor still has 20 yrs left then I bury the pellets at the playground at night ...
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