Erin Doman on June 27, 2016 69 Comments HVAC Troubleshooting: How to Identify, Eliminate & Control HVAC Odors The HVAC unit in your home is one of the most-used appliances, and it’s inconvenient and uncomfortable when it isn’t working. Fortunately, it’s pretty good about giving signs when it needs servicing. One of the key things that many homeowners notice is bad aromas coming from the unit. An odor problem doesn’t necessarily mean that the repair will be expensive. It could be a dirty air filter or condensation which has created mold in the unity. When troubleshooting the smell, use your other senses as well. Listen for banging or knocking. Look for excess water on the ground or other liquids which don’t belong. Many times, the smells are not dangerous, just indicative that your system needs service. However, some smells, like rotten eggs or gas are more serious. If you are experiencing an electrical, burning odor, or gas smell, turn off the unit and call your HVAC technician right away. Here are 5 common HVAC odors and what they indicate. 1. Electrical Odors If your HVAC unit smells like it might be overheating, it very well could be. Turn your unit off before attempting to diagnose the problem. First, check the air filter to see if it is very dirty as this can restrict the air flow and overheat the electric resistance heaters. If it’s not an air filter issue, make sure the electricity is turned off at the master switch. A professional HVAC technician will need to check out the problem and make repairs. An electrical odor typically is a problem within the motor or the wiring. Attempting to fix either of these items can result in severe injuries. In the fall, the first few times the heater kicks on, it may emit a burning odor that can smell electrical and dusty. If you are just turning on your heater, this could be a problem which will eventually go away on its own. Give it 20 to 30 minutes and see if the smell dissipates. If it does, it probably was just the dust burning off. If it continues, contact your HVAC technician. 2. Rotten Egg Smell Provided there aren’t any rotten eggs in your home, then the smell of rotten eggs or sulfur most likely indicates a natural gas leak. Although on its own, natural gas is odorless, most utility providers add the aroma to alert people of a leak. Don’t take this lightly. Open the windows to your home, get out of the house immediately, then call the gas company. 3. Gas Smell Sometimes, when you first turn on the heater, it can smell like gas is burning. During the summer, dust settles within the HVAC on the heat exchanger. When the furnace is turned on, the dust gets burned off. If the smell isn’t coming from the vents, it’s most likely a leak at a pipe fitting or within the equipment. You should not attempt to fix this problem. Call your HVAC technician to find the leak and make repairs. 4. Musty or Moldy Smell A smell like mildew or mold is probably the most common ailment of HVAC systems. When the AC is running, there is a lot of condensation within the unit. When the moisture doesn’t drain properly, it can escape into the ducts and cause mold. Finding where the mold buildup is and getting it cleaned up will solve the problem. An HVAC technician has the knowledge to handle the problem and ensure that it doesn’t recur. Note: Mold and mildew smells are not problems with the unit that are serious, but the poor air quality does increase the risk of respiratory infections in both adults and children. Although you can still use the unit while you’re waiting to make repairs, you shouldn’t put off repairs for the sake of your family’s health. 5. Smell of Oil The smell of oil comes from one of two things. First, look for an oil leak. If you see oil, you may just need to tighten a fitting in the tank, oil line, or filter. While this isn’t a dangerous issue, it does need to be taken care of by a qualified repair technician. It should be noted that a new furnace may emit the burning smell for the first 24 hours of operation, but if the smell continues beyond then you need to call the professionals who installed the unit. If you do not see oil, then the problem most likely is that the oil burner is not working properly. However, there are many things that could be causing the oil burner to malfunction, for example, a clogged burner or a bad fuel pump. Watch for soot and smoke, and listen for unusual sounds. These indicate a more serious problem that should be repaired by a service technician. It’s not only odors that indicate a problem. Puddles of water near the unit can be just as problematic. If you see water leaking from your indoor unit, see if you can trace the water to its source. It could be a leak within the unit, excess condensation, or a tear in the insulation foam. If you don’t know what’s causing the water pooling, call your technician. Dealing With HVAC Odor A common reason that many HVAC units do create more odors is that homes are built very tightly today, often without the necessary ventilation. This causes the unit to run out of air for combustion. This can be the leading cause for foul HVAC odors for many homeowners, which raises concerns about indoor air quality. Another indicator of an indoor air quality problem is the smell of dirty socks. Although this smell may be coming from the air conditioning unit, it is not actually the unit that is the problem. Most likely, organic material has not been heated to a high enough temperature to prevent its growth. In most units, the heat exchanger kills the organic material, but those with heat pumps do not reach those temperatures. When the spores and mold are released into the air through the heat ducts, it produces poor quality air. An HVAC technician can diagnose the problem and recommend solutions. Make sure to replace the air filter according to the manufacturer’s instructions. Have your HVAC system inspected annually by a professional technician to look for faulty wiring, loose or worn belts, and general wear on the unit. By having an annual service, you have peace of mind that you’ve done what you can to make sure your HVAC unit is ready for the seasons ahead.
Mcdoogle says October 12, 2016 at 6:00 pm You stated that a common reason that many HVAC units do create more odors is that homes are built very tightly today, often without the necessary ventilation. Do most HVAC contractors have different things that can install to create more ventilation? My daughter started complaining of a weird smell in her room that was coming from the vent. Hiring an experienced contractor to come and inspect it might be a good idea. Reply
Steve says October 16, 2017 at 1:53 pm Search for HRV & ERV. Heat Recovery Ventilator / Energy (sometimes Entropy) Recovery Ventilator. http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv These introduce filtered outside air into the living space and exhaust inside air. (The intake and exhaust cross paths, each enclosed, and transfer some heat so it is more energy efficient than just opening a window.) Some can also make up pressure drops in the house that occur when the HVAC blower is running. Negative pressure in the living space means the house is pulling some air from wherever it can find it–crawlspace, attic, chimney. Reply
HVAC Help & Handyman says March 11, 2017 at 4:21 pm Great to know in case it happens to you, great article. Thank you for sharing. Reply
vanessa says April 27, 2017 at 10:44 pm My air quality in my bedroom seems to have something wrong with it it also seems as though it’s coming from the air condition I get a sometimes pepper type smell coming from it that bothers my throat as I sleep in as I’m awake it also happens with my fan what could this be it happens nowhere else in the house except in my bedroom when I have either of these units on it’s an oscillating standing fan and a regular window air conditioner two different items it gives me a call and often makes me feel as though something’s in my throat I’m hoping this isn’t dangerous and should I get rid of these items I am not able to pull the filter out in the air condition it seems to be stuck . Reply
sasha parks says July 22, 2017 at 9:05 am I am experiencing the same feeling in my home that we just moved into about 4 weeks ago. I think its the hvac but, my husband and kids cannot smell it at all. At time its so strong it burns my eyes. it is mostly at night in evening. Thank you for the pepper analogy i was explaining it as a smokey smell, and no one could relate. What did you end up doing?? Im going nuts!! Reply
Steve says October 16, 2017 at 1:24 pm Does your HVAC air handler have a UV bulb installed inside? They can sometimes give off odor (from the bulb coating) or by reacting with something inside the unit. We had this happen. The odor was similar to plastic, faint, but very sharp. Reply
vanessa says April 27, 2017 at 10:46 pm I’m sorry I’m trying to tell you that it gives me a cough Reply
Steve says October 16, 2017 at 1:27 pm Bottle up some water straight from the faucet. Take it outside and stay out of the living space for 20 minutes or so and then try drinking or smelling the water before re-entering the living space. Reply
dver says July 16, 2020 at 7:09 pm i also cant figure this same question. did you get an answer? Reply
Cindy says July 16, 2017 at 7:30 pm Why does my central heat and air smell like burned prom please someone help me Reply
rebecca toller says July 24, 2017 at 5:54 am My apartment smells loike car exaught fumes when it turn on and runs it is all electric any idea what would cause this. Reply
Edna C says December 15, 2018 at 7:36 pm I too have that same smell and it’s driving me crazy. I have an oil fired hot air furnace with an a/c unit attached. I’ve been thinking the smell was exhaust fumes, but I’d be dead by now. My furnace is checked anually by a service tech. I wish we could figure this out. Reply
Jean says January 29, 2020 at 11:10 am I’ve been smelling a low odor of exhaust fumes in the home we are renting also. I am the only one of 4 people that can smell it. It’s only when the heat is on . It’s January and I had to crack two windows to air out a couple rooms. It’s starting to give me headaches. It’s driving me crazy! We have smoke detectors installed with co2 monitors. They haven’t gone off. Would love to know what the cause is, and a fix. Reply
Dennis says February 18, 2020 at 8:00 am I am having the same issue. Did you get any resolution? Reply
Kristy Dixon says July 26, 2017 at 11:21 pm There is a rotten egg smell that comes and goes in my home , we do not have any gas appliances nor do we have gas connection. Only electric. We searched for a dead rat/mouse and nothing. Can this be from the drains or air conditioning unit? Reply
Steve says October 16, 2017 at 1:31 pm Have a plumber check your plumbing. You might just have to clean the traps, but you could also have a blocked vent. Sewer gas can smell like rotten eggs, and it can be very dangerous. Also, you could have a gas line on your property even if you don’t have gas service. See if you can smell it outside. Reply
Darla says May 15, 2019 at 8:49 pm Chinese drywall is said to smell like rotten eggs. Have you done any remodeling in past? Reply
James says August 1, 2017 at 9:23 pm Personally, the only weird smell I’ve ever noticed coming from an HVAC system was when my walk-in fridge smelled like nail polish remover, but I noticed there wasn’t any mention of that here, so here’s an article that i thought was insightful for anyone else with an acetone-smelling cooling/refrigeration system. Reply
Vicky Hughes says May 25, 2018 at 5:36 pm I too smell that smell with my HVAC, not sure why, it only comes every 30 or 40 minutes. Strange. Reply
Lacey Simmons says April 21, 2019 at 7:43 am Me to! Today we tried to unclog the washer drain and found a tar/oil substance! Our home is on a concrete slab so most of the plumbing is in the attic with the ac unit! I’m wondering how these 2 are connected… Reply
Lynn says August 26, 2017 at 9:19 pm Sasha, I am having the same issue. I purchased a brand new home. My family and I moved into the home three months ago. As of last week, I began to notice a cigarette type of smoke smell coming from the air conditioner. No one smokes in my household, and no one else can smell the odor. I am sensitive to odors, and this smell is driving me crazy. I now have sneezing fits and an itchy throat. What causes the smoke or pepper smell? Please help. I have changed the filters, but the odor persists. Reply
Al says August 30, 2017 at 4:12 pm Sasha ,we r also having the same problem in our new home. The odor has been in the home since we moved in 2 mos ago,Had all kinds of people to investigate to no avail. It is at its strongest when the AC runs. Had a REMI air purifier installed yesterday. Has not helped yet. I think it is coming from the outside because I smell it around the house. Also, I smell it in other areas of our development. Everyone insists that the AC cannot bring it into the house. BY-the-way, where do u live? We r located in central FL. My wife thinks it smells more medicinal than smoke. Hard to describe but not pleasant. Does anyone know for sure that the AC cannot suck in odors from outdoors? We r also waiting for the results from formaldhyde testing. Reply
Steve says October 16, 2017 at 1:41 pm Ducts leak. When the blower fan is idle air in a crawlspace or attic can infiltrate due to natural pressure imbalances. If your crawl or attic is vented, you could introduce odors from the outside. Also, if you have old hard ducts, the insulation surrounding them can break down or trap moisture and grow mold and that can get sucked into your living space. Read up on those Hydro-Peroxide air cleaners. I won’t put one in our house. (I’m not an IAQ pro, but have been fighting a family mold problem for the past year and reading and reading.) Reply
Eileen Postregna says January 22, 2018 at 10:01 am Last Friday night about 11:00 pm my furnace started and that burning smell like when you first turn on your furnace for the winter came thru the house, I went to the basement but didn’t hear or see anything wrong, I read on the internet to make sure all vents were open, I had 4 vents closed, opened them and I also vacuumed all my floor vents, a couple were pretty dirty. I had my furnace cleaned 2 months ago, I also had a furnace man come out a couple of days ago but he said he did not see anything wrong, should I have my ducks cleaned to get rid of the smell? My furnace is about 19 years old. Reply
Sarah says November 20, 2017 at 12:33 pm We have the same issue in NC. Several HVAC contractors, a plumber and utility company have investigated without resolve. The smell is worse in warmer temperatures, so I assumed HVAC was the issue. I am beginning to suspect Chinese drywall (on a few specific walls) at this point. Especially being in Florida, perhaps check your copper fittings and pipes for discoloration. Phantom smells are so exhausting (pun intended)!! Reply
Christina says September 4, 2017 at 8:28 pm I live in an apartment and the last month or so there’s been a few problems when my ac.. one being the condensation line another was the blower.. another the coil needed replaced i believe. Any way… now i have a weird cat box smell when the unit comes on. I’ve never had an animal. I changed the filter. I hate it. Why is it smelling so terrible? HELP!!? Reply
Kelly says September 17, 2017 at 4:34 pm When I’m at work I sometimes notice a almond smell coming from air conditioning, I will say for sure there is mold in the insulation I know the roof has leaked on occasion and there are dark water marks on ceiling tiles Reply
Stephen says September 25, 2017 at 9:12 am We have the exact same thing in our home…. we moved in March 2017. My wife keeps telling me she smells cig smoke too and non smokers here! Our hvac unit is new. We are puzzled…. did you ever find out anything w your home? Reply
MANOJ kumar says September 30, 2017 at 2:36 pm We are feeling a very bad smell.it is a new split ac of Lloyd. What is the problem.is an ac give bad smell at 28-30*c.? plz reply. Reply
Michael says September 30, 2017 at 8:45 pm Hi did you ever resolve your problem?I have the same issue does not seem to be the sewer pump , I get a egg sulphuric smell from air handler that is then blown through the house Reply
margaret p franklin says October 5, 2017 at 1:37 pm I have a rotten egg smell coming through my vents. I have had the ducts cleaned, the plumber, septic tank, and hvac check the furnace for natural gas leaks. We have installed a humidifier but nothing seems to work. Any other suggestions. Thanks Reply
Jeanne D. says October 13, 2017 at 3:27 pm I’m having the same problem. A rotten egg smell coming from the vents when the ac is on. It isn’t all the time. Usually in the evening around 9:30 for a few minutes then it’s gone. It’s a newer unit (1-1/2 year old). Should I call a plumber or HVAC technician to investigate? Reply
Dianne Fox says September 14, 2020 at 8:25 pm Jeanne: i posted my first post last night, regarding smells coming each time AC or heat comes on. It’s interesting that your specific problem — smells more obvious in the middle of the evening. Mine smells each time one of the units comes on (both brand new, but previous ones did the same) comes on throughout the day, but for some strange reason, the smell is worse at night. Hopefully you/we can find out the cause. Reply
JJ says October 18, 2017 at 8:34 am Our office smells like a dead animal first thing in the morning. We have figured out that it’s on the cold mornings that our a/c doesn’t come on overnight. We’re in Texas so we only get cold days once in a while so we’ve pinpointed the correlation. What would cause the smell when the a/c is NOT used?? Reply
Marshan says October 23, 2017 at 11:46 pm 2 months ago I noticed an old, musty smell coming from our bedroom vent and only our vent. Maybe like mothballs? The ac was not running. When the ac or heat are running there is no smell. Only when there’s nothing running. It is now in 3-4 vents of the house. Our bedroom vent still the worst and when I put my face close to it air is blowing even when nothing is running. I have changed the filter and vacuumed everything I can. Used filter fresheners. Sprayed the filter with essential oils. Only helps for a short time. Going to check the humidifier filter. Reply
Shy says June 18, 2020 at 11:12 am I think the coils need cleaning as well as an outdoor vent that blows filtered air on roof instead of in apartments. Very undereducated individuals ignoring the request to repair for safety issues. Reply
Kelly says November 16, 2017 at 8:57 pm I have a sour smell in the house down stairs when our heat or ac comes on. What can cause this? Our units are new. We replaced the down stairs unit this past summer. Our upstairs unit was replaced the year before. Reply
Ashley C says December 30, 2019 at 9:28 pm I have 2 new units and I am having the same problem. It’s like a soured musty smell. It’s getting worse and have no idea what it could be. Reply
Mary says November 30, 2017 at 2:18 pm My apartment smells in my bedroom and bathroom like mold mildew but can’t find nothing leaking??? Can someone please tell me what could be causing this because I have allergies and unfortunately I’m allergic to mold and mildew, whether my a/c is running or not the smell is awful, especially getting sinus infection and upper respiratory infections because of this problem, and the only area’s it’s coming from are the vents from my bedroom and bathroom area, and I’m tired of my eyes burning and drainage from infections, please someone help!!! Reply
MIKA KAWADA says September 12, 2019 at 2:26 am Hi, Did you solve the smell issue? I have same problem now. and I started be allergies. if you solved, please let me know how to do. Thank you. Reply
James says December 10, 2017 at 9:00 pm My musky moldy smell has started with the heat on in the winter time. Reply
Renee says January 13, 2018 at 8:51 pm please add….dead mouse. Just had the service person to our house for what I thought was a gas leak. We smelled, sprayed the pipes, nothing. Thought my worm farm was setting off the detector. I think he thought I was crazy and then…he smelled it too, Rotten Eggs…! My husband blamed the worms but in the end, it was a dead mouse in a trap next to the furnace releasing the last of its essence. We all had a good laugh – yuck! Reply
Rose uselding says January 22, 2018 at 7:12 pm I get an oily smell from a/c-heatpump. I fristhad a morning or groaning sound from my unit.PLEASE HELP Reply
Stephen says January 30, 2018 at 1:52 pm Hello , i have forced air oil heat , at the end of the blower going through its cycle i get a sweet smell & taste in the air so bad that in winter i had to get out of the place for a while . i had the smell abd taste for about a half hour or more . im a diesel mechanic & know most oil/ fuel/ sulfur smells , this reminds me of antifreeze being atomized but cant be . anyone have any encounters of this or even heard of this , making me sick smelling this! Reply
chuck says March 24, 2018 at 7:05 pm Did you ever figure this out? Im having the same exact problem.. its making me sick too.. Im the only one that can smell it in the house.. Reply
M H Ferrell says February 4, 2018 at 5:50 pm I live in a senior manor complex there are 4 apartments in each housing unit. Two on right side of building and two on the left side of building. I moved in 4 months ago and have had this smell that to me is very strong. Don’t really know how to describe it, kind of sweet, sickening smell. The units are at the back of the building and the frontroom closet has the unit. I don’t know if it has been serviced or not just want to know what this smell could be. Reply
Joe says February 5, 2018 at 6:04 pm Blower motor going bad? dust on motor could be “cooking” when motor gets hot? Reply
debi says March 6, 2018 at 8:25 pm I rent a house with a connected garage. y landlord works on cars in the garage. i have lived here for 7 months and never had any odors in the house. about 3 weeks ago my landlord began working on the cars in the garage ans spilled some gas and didnt clean it up. i got the strong smell of gas in the house right away which probably come thru the connecting door. i opened the windows and cleared it out but the fume odor has never gone away totally way and its been 2 to 3 weeks. now. every time i turn the a.c on i can smell a fume type smell in the air coming out the vents and smells up the whole house and makes my eyes burn and i get headaches and nausea. could the original odor of the gas be saturated in the duct work and i get it when i turn the a/c on ?? the connecting door has been sealed off so the smell is coming form the a/c vents. how can i get rid of it and it seems to have a negative effect on my health. Reply
Stephen says March 9, 2018 at 8:33 am Yeah i did all that made sure all solvents and everything were not leaking , turns out for me , ear nose & throat doc says sinus infected , fluid trapped in head needed surgery to correct & there is a condition called phatom something which causes smells & tastes where source cannot be detected . NBC did a show on olfactory phantom smells & tastes which my doc says is a real condition people can have . after having others in my apartment not smelling anything , but i was smelling it like crazy , determined it was me that was creating the smell , & yes my hygien is tip top smart asses !! Lol Reply
Fran says April 5, 2018 at 4:46 pm I find that when my husband turns up the unit to eliminate a smell of cooking we get a metal smell in the house? Any thoughts. How do you clean the large filter and how do you clean the unit if you have spotted a little mold? Thks Reply
Delores says May 8, 2018 at 11:48 pm I have this problem with my furnace. At first the furnace will be on, and I will smell a very strong odor coming from out of the vent that will burn my eyes and nose and give me a headache. When I leave the house to smell this all on my clothes and we’ll get on other people close, when the furnace is shut and I’m sitting by the vent the smell comes out of the vent. I cannot describe the smell no more than just to say it is a very bad disturbing older, 1-minute smells like a mice piss, something dead, it is just horrible and it stinks. Help!!! Reply
Joe K. says June 6, 2018 at 3:13 pm If you have national gas . Have them come out and check with there snifer. We had a funny smell everytime the heater came on and when the a/c came on also. They came out and found 2 slight gas leaks. One was by shut off valve and the other the other tenants had a gas dryer and never capped it off. and gas was coming out of there. .35 what ever that means. since he did all that we have not had that funny smell now for over a week. Good luck. Reply
P.B says May 11, 2018 at 2:30 am I bought my home a year ago on the 17th of this month. This is the first time that I’ve noticed that when the air comes on it smells like pet odor. Like animal pee. I do not have any animals and nothing at all smelled like animals when I moved in. Everything has been redone and there is no odor when the heat is on. It’s coming through the vents in the floor. I am curious if an animal is peeing close to my house and it’s coming in that way. Not quite sure why it would smell like that as I never see any stray animals around either. Reply
Trish T. says July 30, 2018 at 6:34 pm Our AC stopped working due to clog in line, we cleared it up and now the house instantly smells of cat urine? Reply
R D says August 20, 2018 at 9:41 am We are expierencing an odor like maple syrup. It’s just started within the past few weeks after it was serviced. The unit was low on freon. Has anyone had this, or ever heard of this problem with a central HVAC system? Reply
Michael says November 18, 2018 at 9:58 am Any tips on how to compel an apartment complex manager to take action on these kinds of odor problems? The maintenance man says he can’t smell it when I showed him. He either has no sense of smell from decades of chemical use or doesn’t want to admit to the smell because it would result in work for him. Reply
Jane may says January 10, 2019 at 6:37 pm I have a unit in my Mobil home and the smell coming from it burns my eyes throat,it smells like some kind of chemical.it’s driving me crazy.can someone help.they come out and cleaned the coils.it didn’t help. Reply
azi says February 8, 2019 at 12:34 pm I had a smell of “old”, “stale”, maybe you’d call it chronically unventilated–even though the AC was running and cooling fine. I had no idea where it was coming from, and I did not think it was my AC…..until: I was taking apart an old shop vacuum one day, as the noisy motor needed its bearings replaced and as soon as I’d extracted the motor from the housing–WOW!–did I ever smell the stinky smell in question to the tenth power! The old motor was caked with smelly dense dust! Could other motors like the one in my HVAC (26 years old) be doing the same thing? I ripped apart my air handler and pulled out the filthy, dusty, stinking motor! I half disassembled it to not only get to the parts and clean them well, but to facilitate adequate drying over the next couple days. On reassembly the smell is GONE! Reply
Jim says August 24, 2019 at 2:29 pm I see a lot of comments, very similar, about odor/smell issues. I too have that. My wife does not smell it. Sometimes I smell the same odor in our car which makes me believe it is the HVAC. But, I don’t see ANY ideas or resolutions. HELP! Reply
Kent Bernard says July 20, 2020 at 12:11 pm Has anyone discovered the cause of the odors that smell like gaseous fumes or exhaust? The heavy, sweet, sickening odors that linger low to the floor? Reply
Dianne Fox says September 13, 2020 at 10:29 pm Need help! I have brand new air conditioner and gas furnace. Had ducts cleaned professionally. Changing filter as recommended. Each time air conditioner comes on, it smells terrible the entire time it runs. Old furnace did the same thing, too. Haven’t used new one yet, so don’t know how that will go. HVAC people don’t know what to do. Is making me sick. Reply
