Why Does My House Smell?


Yes, that’s your illustrious author making the “stink face”

People often ask: “why does my house smell?” Often, this is during the winter because your house is sealed up for months, with little fresh air. In fact, with tight, energy efficient homes, this has become even more of an issue. It’s one of the reasons that there’s been a backlash against tight houses.

#1 – your house might not be adequately ventilated

First, let me address the energy efficient house issue. The problem is, many builders and architects don’t understand that a house is a complex system. You can’t just air-seal the house and have a healthy house. That’s why building best-practices call for a certain amount of fresh air circulation. So if you live in a tight house, you want to ensure you have adequate fresh air or your house will get stale and smell. If you don’t know about HRV’s and ERV’s (heat recovery ventilators and energy recovery ventilators) read this short post. Every modern home should have one of these. Once you’ve lived with one, you’ll wonder how you managed without it.

#2 – there might be a dead mouse/animal somewhere

During the winter, mice and other critters want to come in from the cold and live in your home. In my area, the field mice flood in ever winter. This can be reduced by having a well sealed house, but they’re clever and they’ll find any little opening to get in.

Invariably, some of these will die in your house, leading to a horrific smell. You’ll think the sewage lines are overflowing. It’s really nasty. The only solution is to take a good flashlight and follow your nose. Yuck! But if you don’t track it down, you’ll have to live with the odor for months.

Note: I’ve found many dead mice inside the air handlers (behind where the air filter goes). If the dead animal smell seems to be everywhere in the house, open the air handler and look for dead rodents.

#3 – sewer gases? Your drains might not be dried out or improperly vented

We all know that stink. You’ll look suspiciously at the dog but you won’t find the ‘evidence’. Sometimes the smell will disappear, other times it will remain for days. You might be the victim of sewer gasses!

In most homes, the problem may be as simple as a dried out sink trap. The sink trap is the little ‘U’ under the sink in the drain line. This is supposed to be filled with water. This acts as an odor plug that prevents gas in the drain lines from coming out the sink. If the trap is empty or too low, the odors in your drains, which are all connected together, waft out into your home, leading to the ungodly stink.

If you discover that the odor comes from your drain, simply run the water for a few seconds to fill the trap. Once the odor has diminished, this should prevent more odors from coming back in.

If the sink is in an infrequently used room, like a guest bathroom, the trap may be drying out by simple evaporation. You can greatly reduce the evaporation by adding a teaspoon of vegetable oil to the trap after filling it up with water. Don’t run the water after doing this because that will flush out the oil. You want a thin layer of oil on the surface of the water to prevent evaporation.

As a side note – if you plan on leaving your house for a while, like going on vacation, add some oil to every drain in the house to keep the traps from drying out. You’ll thank me when you return.

Improper venting:

Sometimes, the trap gets the water sucked out because the air vent is clogged or non-existent. You know those 2″ pipes that come out your roof? Those are connected to the drain lines. If you sniff them, which I don’t recommend(!), you’ll smell sewer gas. These allow the sewer gases to float up and away but they also allow the pressures in your drain lines to equalize so when you flush the toilet, or drain the tub, it doesn’t create a vacuum in the pipes which sucks the water out of the sink traps. You can hear it when this happens – other drains around the house might gurgle or toilets might mysteriously drain. That’s indicative of bad drain line venting. If you have this, explain the problem to a plumber and have them fix it. This isn’t usually an issue that a homeowner can fix.

#4 – is the smell coming from your air conditioner or furnace?

There are a few possibilities here.

Cat pee/urine/piss smell – typically, people associate ammonia with cat urine, so when they smell ammonia, they immediately scold the confused cat. Then, as the problem lingers, and they notice the smell coming from the ventilation ducts, they realize their error and start searching in the right place.

Sometimes, it’s a mouse-house inside the air handling system. They love warm places and they urinate everywhere. Gross! So if the smell comes from one vent in particular, open the vent and check for shredded material or caches of food that indicate the mouse den then clean it up with a vacuum cleaner and some warm soap-water or baby-wipes. (pro-tip: baby wipes are great for cleaning just about everything!).

If the smell comes from everywhere in the house, rodents may be living in the air handler. Usually you can open up the air handler and look behind the air filter for signs of mice.

You might also have tainted insulation. Some blown-in insulation products contained compounds that smell like this. Any leaks in the duct system allows those smells to be distributed throughout the house. You can easily determine this problem if you stick your head in the attic and sniff. If it smells the same, that’s your problem. See “Mystery smell” below for more on this.

Musty/moldy smell – This one is usually much easier to find – this smell is associated with water/moisture in the system, leading to mold growth. When air blows through the system, it circulates the smell from the mold source and your entire house gets that musty smell.

Mystery smell – dusty, “hot”, etc – Poke your head into the attic on a day when it’s hot up there and sniff. Does it smell like what’s coming out your vents? If so, you’ve got leaky ducts, usually on the return (air intake) side of the system. This is really common – when your system runs, it sucks in air through the “air return” line. If there are any holes in that line, or in the attic mounted air handler, it will suck in dust and any odors from the attic and distribute that throughout the house.

Solving this issue can be as simple as looking at the system in the attic and finding holes. Usually it’s not that simple and I recommend a professional come in with a “duct blaster” to test and seal your ducts. Sorry, but that’s the best and safest way to track these smells.

#5 – stinky bathrooms?

If the problem is the normal, um, stinky bathroom, you need better ventilation. Most homes have exhaust fans in the bathrooms, but few work optimally.

The first test is to put a sheet of paper or strips of tissue up to the fan. It should strongly suck the paper onto the vent when the fan runs. If it doesn’t, the fan doesn’t work properly. Most fans have too much duct attached which significantly diminishes the flow. You want a short, direct path from the fan to the exhaust on your roof. I’ve seen people with 50 feet of duct connected to the fan, rendering it useless. Trust me on this, the shorter the better, and best to go straight up through the roof if the bathroom is right below the attic.

You’ll want to invest in a high quality metal roof vent like this one. These last forever and are self flashing (minimizes the chance of roof leaks) and are easy to install.

In addition, the fans only work if you use them. Let them run for at least 15 minutes after you “do the deed”. This is about how long most fans take to flush the stinky air out of the bathroom.

#6 – musty basement

Musty basements mean damp, moldy basements. If you’ve got a wet basement, you need to do whatever is necessary to keep it dry. I’ve written a lot on this, as have others. A damp basement is unhealthy and can lead to serious damage to your home to the point that it becomes structurally unsound. If you try to sell your home, it will be flagged by the home inspector and you’ll be forced to fix the problem. So if you have a wet basement, fix it *NOW*. Then, you can enjoy a safer, healthier, less smelly home for the rest of the years you live there.

Got any other home smell problems? Drop me a line and together we can figure it out.

99 thoughts on “Why Does My House Smell?

  1. Very comprehensive article Ted, we recently moved to our 2 years old house and updated the whole ducts and removed dead raccoon from attic. But there is a strange smells coming from some of the vents, especially night time. And also on first blown whenever air conditioning turn on and then it goes away. Few companies check and has no idea what could be the reason. Smell is very sharp but only start when sun goes down. Any clue or suggestions you might have for me?

    • When the air first comes on, the air has been still so odors accumulate and are blown out initially. As the system runs, the flowing air dilutes the odors. However, that leaves the main question-“what’s that smell?”
      What type of odor are you smelling? I had an issue like this with my parents’ system and found a dead family of mice in the air handler. I didn’t find them until I opened the system as they had nested in a little nook that wasn’t immediately visible. Come to think of it, that happened in my car too. Mice nesting inside the blower that required the to dismantle it.

  2. Hi..one of our rental homes has a strong odor in the 2nd floor within the walls (can detect through the light switch box I just replaced) most noticeably on very hot and humid days. Smells like musty stale attic type smell. I was concerned about mold but don’t believe it is. Would an exhaust fan in the attic help remove this odor and keep heat from pushing into 2nd floor along with the smell. Not sure what to next or who to call

  3. On warm days, especially sunny ones, when the windows are open it seems to draw a synthetic almost rubber smell from the walls. This smell is present in multiple rooms in the house both on the main and upper level. There does seem to be some sort of connection between the windows being open and the smell being stronger.

    Thanks for the help.

    • It’s funny you should mention this. At the exact moment I saw your message, my wife said “what’s that smell? It smells like cigarettes!”
      We had recently opened up the house on a beautiful spring day. In our case, the “flushing of the air in the house” is likely creating a slight vacuum that is pulling air down our chimney and through the living space. The ‘stink’ in our case also smells kind of smokey/burning rubbery. I think it’s the smell of creosote in our chimney. It is described as: “Creosote has a strong, smoky smell, and can smell like a fresh-paved driveway made of asphalt. The smell of creosote can be likened to the smell of tar, and this creosote smell is easily picked up by the human nose even in small concentrations.”

      It it possible that is what you’re smelling too? I know you said it’s in all the rooms, so it might not be this, but it’s worth considering. Is it possible that the smells are circulating via the air conditioning ducts and spreading everywhere?

  4. We have a sweet smell that is very strong in our return duct (which runs under our house, in the crawl space, and then up into a return box). If i stick my head in the return duct the sweet smell is very strong. It isn’t strong when I open the furnace and smell in the return box but it is still noticeable. When i turn on the heat or A/C, the smell mainly fills up around the furnace but some also comes out of the registers throughout the house. When i put bowls of charcoal and coffee in the return duct, it sucks up the smell pretty well but it comes back that same day when i take the charcoal and coffee out, even without turning the system on. We had all the ducting throughout the house replace three months ago and it started about 3-4 weeks after that. We’ve had all the ducts scoped and cleaned and checked the furnace for CO. HVAC duct installer came back and couldn’t figure it out.

  5. We moved into our newly renovated “flip” home 4 months ago. Our house smells awful. We are the stinky people now. Al
    Our clothes, towels, bedsheets, everything smells like old wood, musty, dusty smell. It’s so freaking stressful. We have air purifiers, diffusers and a super clean home. We just bought two power vents to go in the attic, hoping that will help get some heat out (Louisiana). I’m scared we have mold somewhere. Could it be cheap paint or drywall? It’s strong everywhere, but worse in the garage and my kids room. We do know an old smoker lived here before. We tried an ozone machine and that did not work. Who can I call to test or just figure this shit out. I want to move!! My clothes stink!! Ty!

    • That sounds awful!
      Does the smell increase or decrease at all? Do you think it might be worse when the air conditioning or heating is running? Can you smell it stronger near the heating or cooling vents? If yes, the there’s a good chance that the problem is leaky ductwork that’s sucking in the odors from wherever the ducts and heating/cooling system is installed.
      Another possibility is that the odors are coming from under the house, like from a crawl space. Air and odors like to move from low to high in a house so often they start below and work their way up.
      Have the odors always existed? Are they worse when you run the power vents? Those power vents are notorious for causing problems inside homes. Studies showed that in many homes they cause electricity bills to go up because they suck air from inside the house up into the attic. This could also increase odors because it will also suck odors into the house. Mostly, the power vents do more harm than good.

  6. Hi. My 3rd floor smells when it gets really hot out. It smells like rotting garbage. My son’s room is up there. We orignially thought it was stink bugs, but we bug bombed the house a few weeks ago, it’s 90 degrees and it reeks. This has been happening for the past 2-3 years. Any ideas?

    • I forgot to add. I originally thought it was mold growing on the roof. There were streaks on the roof that looked like wet marks from rain that just never went away. I had the roof professionally treated. It didn’t help.

      • I would have thought a dead animal, but that smell wouldn’t last for years.
        Odors are definitely intensified by the heat which releases smells much more readily then the cold. You say it smells like garbage do you think it smells more like rotten food type of garbage or more sulfurous? The reason I ask about a sulfur smell as you may recall that controversy with the Chinese drywall that was releasing horrible odors like that and had to be replaced. do you think it’s possible that this may be the source of the odors? have you got up into the attic to see if the odor is more intense in the attic? If the odor is stronger in the attic then that rules out the drywall. If the odor is more intense inside your son’s room then in the Attic, that supports the drywall theory.

  7. I smell a musty smell mostly from one floor vent only when the Air conditioning is running. I don’t smell it in the winter when the heat is running. There is a faint hint of it in a couple other floor vent/ducts but it is strongest in one room. Any ideas?.

    • Musty smells in air conditioning systems are quite common because air conditioners extract water from the air. That water pools up in a pan underneath the air conditioner and it’s supposed to drain out but a lot of times it just sits there getting moldy and nasty.
      the strength of the smell could be due to a number of reasons but it is highly likely that the source of the smell is inside the air conditioner.
      you can also have mold growing on various parts in the air conditioner so good cleaning in the spring if usually called for. A service tech will take the system apart and spray down the coils replace filters Etc.
      one other thing to check is if you have a humidifier built into the system they often have sponge-like elements that get really nasty.

      • Thank you so much for your prompt response. I failed to mentioned it is central air but maybe you assumed that. What kind of technician do I call? A heating and air conditioning company?

      • If you have a heating/AC company you trust, give them a call for a spring cleaning/inspection of your air handler for mold/musty smells and cleaning of the condensate lines (these are the pipes that let the water collected to drain out of the house.) Often the condensate lines plug with sludge and need to be blown out under high pressure.

  8. can newly installed laminate flooring cause an ammonia smell throughout the house? No glue was used during install. flooring was installed over tile, and moisture barrier underlay was used, but the smell seems to be getting worse each day. When floor was first installed it smelled of wood, like particle board or sawdust-ish. That smell has given way to pretty strong Ammonia smell. any recommendations or, more so, is this odor dangerous for us to be inhaling aside from unpleasant?
    Thank you

    • An ammonia smell with flooring isn’t uncommon, especially during the winter when the house is closed up. When possible, air the house out as the smell will get stronger and stronger if it’s allowed to build up with the house all closed up.
      If you have ventilation fans that vent outside, like bath fans or a good range hood, leave those on. They’ll suck air into the house and flush out the stale air which will dilute the odors, making it healthier. You don’t want to be stuck breathing chemical fumes. Leave the fans going until the odors have been flushed out to an acceptable level.
      Note – some range hoods, like those over electric stoves, do not flush the air out, they just filter the air and blow it back into the house. Unless you know a fan vents outside, don’t bother using it since it won’t do any good.
      I would also crack open the windows in the bedroom at night so you get more fresh air in the house to breathe while you’re sleeping.

      If the smell is particularly strong or doesn’t dissipate over time, you’ll want an air-quality specialist to come in and measure in order to determine the source of the odor and recommend a solution. You certainly don’t want to take any chances with your health. My recommendations above are fairly generic assuming the source is just residual chemicals in the flooring that would diminish in a relatively short time with good fresh air flow.

      Also, see this article

  9. Hi there we are one week in from ” the beast from the east” during the storm my sons bedroom started to smell really awful. The smell is a cross between eggy and rotting cabbage I’ve check for leaks etc and non to be found. My sons bedroom is above the garage and there is no smell there and there is no water damage to the plaster ceiling in the garage. Above the garage door we have vey vey small air vents probably 1.5 cms wide and 5cm tall. The smell appears to worse when the heating is on. Do you have any ideas please

    • Two likely possibilities: the sewer gas vents aren’t functioning properly and you’re getting those gasses back into your home or something died in your ductwork and is rotting.
      Normally, the rotting cabbage/egg/sulfur smell is from sewer gas. This can happen if any sink or shower/tub drain traps dry out, allowing the septic smells to waft out. Take a sniff of all your drains (sinks, bath, shower) and see if the smell is any worse there. Then run water in every sink for a bit. It doesn’t have to be much, just a cup or two will refill the traps.
      If it’s just his bedroom, smell any air vents going to that room. Also, if there’s any closets or dark corners, check for dead mice.
      Good luck! Those are horrible smells!

  10. http://i0.poll.fm/js/rating/rating.jshi there! i moved in to a detached bungalow 3 months ago, and have since noticed a really pungent smell coming from the front hallway area, especially when it rains or snow melts. the smell is a sort of sickly sweet musty smell. the house was built in the 60s. the house is L-shaped, with the front door at the inner corner of the L. i removed ceiling tiles in the basement below this area, but can’t smell anything there. i removed old tiles from the front hallway, thinking the subfloor might be rotting, but it was fine. the vent is not smelly, and it’s not near any washrooms or the kitchen. i’ve stuck my nose in every corner of the hallway and closet, but can’t pinpoint the source. could it be mold?
    thanks for any ideas!

    • sounds like you’ve made a good start with your detective work! that type of voter is often associated with a dead animal. smells awesome come and go with humidity because I think the moisture releases the odors.
      it’s possible that it’s mold somewhere inside the walls they’re usually I don’t get a sweet smell but perhaps different varieties have different odors. mold definitely smells musty as I’m sure you smelled before.
      it is possible when it’s raining or snow is melting that water is leaking in from somewhere outside but I would think you would have found it when you remove the tiles in that area. you might also try tapping on the floor with a broomstick or something solid. as you tap across the floor you should be able to identify the sound of a normal floor and anything different will sound hollow or make a thud. you can do this around the wall near the floor level since that’s usually where issues start. Tap-tap-tap-thud is a giveaway that something is wrong.
      smells can be really hard to pinpoint. they can be carried on the air and come out from somewhere away from the source.
      I was going to suggest removing the air vents for the AC or heating system and looking into the ductwork. I’ve had mice crawl in there and die before. even if you don’t necessarily smell the smell when you sniff around the vents it’s still possible there’s something in there and you only smell it when the air is moving a certain direction.
      I hope that gives you a few things to try to look for. Good luck I know these things can be maddening.

    • That’s a weird one. Could it be coming from a hot attic? That would be strange this time of year but possible.
      Have you lived there for many years or did you move in recently? I ask because I am wondering if this is a new smell or something that has been going on for a while.

    • I’ve got this same “dry wood” or general “wood” smell when the temps get hot/humid. It comes and goes. I think it could be the attic over the garage which has this brown particle board (not sheet rock).

      Karen, did you ever figure out where your “dry wood” smell is coming from? My house was build in the 1940’s – in very good shape but this smell is horrible and gets into clothes.

  11. https://polldaddy.com/js/rating/rating.jsWe just added two walls to close in a patio and pulled our electrical thru the wall to make it our new laundry room. It is roofed in. Stucco on outside. Inside still framed. We started noticing a cat per smell only on days it would rain or shortly after. We thought it was our washer and since have replaced it. Now it is doing it again. I freaked out and removed all drywall and insulation thinking something got wet. So I have just framing in new area (outside walls are done, just not inside). Ran the washer and BAM cat pee smell is back (it rained yesterday) . So it can’t be the washer because this one is different. Can’t be insulation because I removed it. What can it be that when I turn on my washer 10 min later I noticed that smell. (And we don’t have a cat)

    • So it only smells when you run the washer and on humid days?
      Humid days are understandable as humidity brings out odors.

      I can’t tell from your message if it smells when you don’t run the washer but it’s humid out. But it sounds like it’s much worse with after the washer has run.

      Here’s a test – you know the drain pipe where the washer waste water is pumped? Usually, that’s open with the washer hose just loose in the hole. What happens if you take that hose out of the drain (when the washer is NOT running!) and pour a pitcher or two of warm water down the hole? Do you notice the smell? If you sniff the drain hole (yes, this is gross, but it will help locate the problem) is the odor present there? How about the end of the hose from the washer? (unlikely since you replaced the washer).

      It is possible that the house drain line that the washer hose goes into is cracked. Is it possible to trace the drain line down the wall and see if there’s any water leak there?

      Check those things. It should help narrow down the problem.

      • We had the same smell every time we ran the window mount a/c unit. After weeks of trying to find it, I inadvertently touched the wall above the outlet the unit was plugged into. HOT! Turned out the outlet was over heating and slowly but surely melting down! Days, maybe hours from a house fire!

  12. 1950 wood house no pets ..when room temperatures are over 85 degrees ..an ammonia smell comes .only one bed room…(this house does have termites) my only pets lol..house is on piers 2.5 ft off ground..sealled with cross air vents no animals can get in under house. This goes on for over 3 years since I’ve owned it.

    • Many possibilities, but here are some of the most common:
      – Rat and other animal leavings smell of ammonia
      – Fertilizer – ammonia is a primary component, released at high temperatures.
      – Some other rotting materials. Could be an insulation product used in construction.

      Odors release more readily under high temperatures, so that’s not a surprise.
      Do you have an air conditioning system? Or a humidifier? You can get nasties growing in such systems that release ammonia odors. Central air conditioners with ductwork are also hidouts for critters, but since the problem has existed for years, I’d have to guess some building product that is outgassing. However, with older houses, there should have been plenty of time for all such odors to have disappeared.

  13. https://polldaddy.com/js/rating/rating.jsHi Ted,
    We have been having a pungent fermented soy beans smell in the apartment. The smell moves around in our living room and one part of the kitchen that is closest to the living room. Mornings smell worse than evenings. So far, the bathrooms and rooms don’t have the smell (yet). We live in a humid country in Asia. We live in a small 3 story apartment and have the roof above our apartment. We first thought it was someone cooking the Asian fermented beans dish but it doesn’t seem to be the case as the smell is only from our apartment. It is slightly better if we have the air conditioning on. We have tried airing out the apartment as well but no change.

    There has been construction on a site next to us which could have disturbed piping. Recently we have had a lot of rain and the drainage in front of the building next door was not working properly. One side of our roof was also not draining that well.

    Could this be mold or drainage problem? But why does the smell move around the apartment? Who should we call to check this out for us?


    • Hi Kim, you’ve stumped me!
      The only thing that I can think of is that in the living room and kitchen area there may be some places where the air is getting pulled into the apartment from outside, or wherever the odor is originating. It can be quite tricky to find. Imagine that the air carrying the odor, is moving through the walls and floor, trying to find a place to come out. It reaches a hole in the wall, maybe for a pipe or power outlet or even a doorway (since behind the trim it is open to the wall cavity.) From there, it enters your living space. But the source could be anywhere.

      Now, understanding that the odor could be entering through small cracks or openings like that, look around the walls where the odor seems the strongest. Are there any openings you can see near there? As noted, this could be trim around doors with gaps between the trim and the wall. It could be power outlet plates, anything like that. You really have to use your eyes and nose and play detective.
      Once you think you’ve found the area, you can temporarily try to “fix” it with a product like “Glad press-n-seal” which shouldn’t harm your paint or painter’s tape. This is just so you can seal areas up and see if the odor disappears. If you manage to locate the area where the smell is coming in, you may be able to use caulk and seal it.
      This won’t tell you where the smell is coming from originally, and it may find other areas to enter your apartment, but it may help provide some relief.
      Rain and humid weather often bring out odors, so this could very well be what cause the smell to increase. It could also be why the smell improves with air conditioning as air conditioning removes humidity from the air.
      And you never know what is being released when they do construction. Odors are carried on air currents and spread in the air. It would seem to move from place to place as the air moves. For example, if you open a window in the kitchen or turn on a fan, it could cause the air to move from the living room to kitchen.

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