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.


49 thoughts on “Why Does My House Smell?

  1. Hi Ted,
    i have been having this reoccuring smell of sewage/dead something only in my front foyer for months. i have one vent there and below the foyer is a crawlspace. it smells like to me it’s like damp, warm sewage. at first i thought it was a dead mouse but looked everywhere and no mouse. and then i thought it was leaking sewage. i had a plumber come out and he coiuld not find any water in the crawlspace and no other smells of this sewage near the pipe where the toilet water runs through. there was a strong odour in the furnace room but when we looked – no dead mice there either.. we also went through the crawlspace and the smell was not noticeably stronger there, nor was there any water. which kind of ruled out the dead animal in crawlspace theory. i do have a humidifier next to furnace which is supposed to keep the air moist. do u think that’s it? i am scared i am breathing in bad air.

    • Hi Rachel, these types of odors can be really hard to track down. I’ve had some in my own home that took a lot of detective work to find.
      I would definitely recommend checking the humidifier because those can get really disgusting. Often, they have an element in them that is like a sponge. Water saturates this and as the furnace’s air flows pass, the water evaporates, adding moisture to the air.
      The problem is, most of these are rarely, if ever maintained and they are a perfect breeding ground for bacteria and other unpleasant microorganisms. The result can be a sewage-like odor.
      The unit will have a door on it for accessing the sponge-like part. You could open the unit and inspect the element. A simple sniff should be all it takes for you to determine if this is indeed the problem.
      If it’s not that, then it might be that drain pipe. Even though it’s been inspected, it’s easy to miss a crack. The odors can come up through the crack without a noticeable drip. I had this in my home for months before I located the crack!
      Hope this helps. Let me know what you find.

  2. I’ve been struggling with a musty smell in my house for quite awhile. I definitely notice it when the fan on the furnace or air conditioner is blowing. If I stand across from a vent I will notice it – in several different rooms. But I can’t track it down. Do I need to have someone examine my vents and ducts? How to I find someone who doesn’t just want to sell me duct cleaning? This is a great blog. Also we have cracks in our basement floor. I’ve just been filling them. Could the furnace be picking up a musty smell from the cracks and then blowing it around the house? Thanks for your help.

    • Actually, your problem sounds similar to the one Rachel just asked on this discussion.
      Do you have a humidifier attached to your central system? If so, these often get musty and can lead to noxious odors spread around the house. Is this a possibility with your system?
      If not, check back with me and we’ll review some other possibilities.

  3. Also wanted to add we live in the south so in the summer its pretty hot and humid. Which I find odd that it doesn’t smell in the summer. We have electric heat, no gas. And we’ve painted all the walls too.

  4. We bought a house in 2013 and once it got cold noticed a musty/old person smell but couldn’t locate the source. A mold test revealed we did have low levels of mold. We called a mold specialist company and they could not find anything and suggested we clean ducts and air handler in attic. Upon cleaning we discovered there was mold in air handler. We had it replaced as well as unit outside and the ducts cleaned. The following winter we noticed the smell again. We had the AC guy come and check unit and he said it was fine (no mold) but cleaned it and the smell went away. Once again it is getting cold and we notice the smell. When you first walk in you can smell it and then when we leave we smell it on our clothes. The home is a little over 30 years old but has been updated. We have a dirt crawl space covered with a plastic liner, but do not notice a smell under there. We have checked for water leaks and dead animals and did not find anything.

    The chimney leaked at first and because we have tons of pine trees and lots of shade the brick would hold moisture and salts come through on the inside which kind of resembled mold. We cleaned the inside brick and repainted it and the outside was repaired and sealed to keep moisture out. We thought this may have been the culprit but it does not smell.

    The people that lived here before us had big dogs so we kind of thought it might be the wet dog smell. We have had the carpet replaced.

    We do have copper pipes under the house but I don’t smell or taste bad water. There isn’t a urine or sewage smell. The bathrooms don’t smell. It’s not the same smell when we first moved in but the closest I can relate it to is like old people. I’ve racked my brain on what it could be and am considering replacing duct work in attic. Maybe that is still holding smell from however long there was mold in air handler? However the people cleaning the ducts said they really weren’t that bad. Also think I will call Biosweep this week. Do you know anything about Phocatox? Sounds like this would get rid of the smell, and deal with mold, just think it might be a little expensive. I’m getting a little desperate for a solution though.

    Thanks for any advice you have!

    • It’s fairly common to have odor build up during colder months because the house is closed up so you’re not getting fresh air this time of year. During the summer, you’re much more likely to flush the air out with fresh air during nice days.

      From your description, it does sound like something related to the air distribution system. You wouldn’t by any chance have a central humidifier built into it, would you? If you do, then that is very likely the culprit. If not…

      You noted that you had the heating system replaced but not the ducts but the ducts have been cleaned and inspected. That makes it seem very unlikely to be something directly related to the system, though it still could be that the system is sucking in and distributing stale air around the house. Do you notice the smell being stronger in any particular locations around the house? How are the ducts routed? You noted there are ducts in the attic, and leaks up there are a definite possibility. One good trick that I’ve used is to seal up all the duct inlets and outlets around the house, and then using a duct testing fan, blow theatrical smoke into the system. The smoke seeps out any leaks in the system, quickly showing where leaks are. You might contact some energy auditors who do duct testing and have them run a test like this. Most probably won’t have heard of this test, but you might get lucky and find one who could do a duct test.
      Barring that, it’s also possible that they routed the ducts through the walls using the wall cavities as the ductwork. This is frowned upon but commonly done. The problem with this, of course, is that the wall cavities are not intended to be air tight, so circulating your breathing air through them is problematic. Unfortunately, if this is what they did, then fixing the issue can be a real pain since you’d have to run real, sealed ducts through the walls.

      Any other clues that you can think of? It sounds like you’ve been racking your brain on this for a while!

  5. We moved into an older home 1.5 years ago. After a few months there was a heavy smell in my son’s room. We could not figure it out. I turned out to be the bed, it smelled like compressed wood was gassing (it was a captains bed), but none of the other wooden furniture was effected. The smell was so bad that we had to get rid of the bed, and even get a new mattress because the wood smell permeated the mattress.

    We got a pine bed, same problem with the wood. It only happens with that corner of the room. I put a sheet of heave plastic under the bed, taped to the floor and wall, it helped.

    We thought there might be moister from the a new bathroom installed right under that corner of my son’s room. We had walls opened in the bathroom to check the vent pipes, it uses auto pipes, which are legal and there is no mold.

    We had the floor removed and had a sheet of barrier material (water, smell proof) installed. We aired out the room, no smell. We moved the bed back in, the heavy smell was back. We moved the bed to the basement, the bed does not smell. The original captains bed was in two previous homes with no issue.

    Question – what can draw out the smell of wood, especially the support boards under the mattress. We obviously have been worried about health issues breathing in that air.

    • Wow, that’s an unusual problem.

      I believe that you were correct in your suspicions about this being moisture related – few things bring out odors as much as warm, moist air.

      Even if the bathroom vents etc. aren’t leaking or moldy, there still could be considerable moisture escaping the bathroom. You might get an inexpensive humidity sensor like this (<$20 on Amazon) to place in that area to check the humidity.

      Here’s an experiment – put the humidity sensor in that corner and check the reading throughout the day. See if it changes after the shower below has been used. It might take an hour for the humidity to get up there or it could be almost immediate.
      Part two of the experiment is to lay a large sheet of plastic over the humidity sensor and that corner of the room. This will exacerbate the issue as the moisture will build up under the plastic and give a very high reading if moisture is leaking into that corner. I wouldn’t be surprised to see nearly 100% relative humidity after a shower.

      If this happens, then you’ve definitely got a moisture issue from the shower and can attack it from there.

      Note that the moisture issue should be taken care of in the bathroom, not above it in the bedroom or you risk trapping moisture in the floor and walls which could lead to serious problems. The builder should have installed waterproof barriers in the walls of the bathroom around the shower to minimize the problem of moisture escape. Also, check the bath fan to ensure it is sucking hard – you can do this with a sheet of paper held under the fan – it should suck up to the fan strongly. Also, pull down the fan cover and ensure that the fan’s housing is sealed to the sheetrock of the ceiling. Almost nobody does this but without a water-tight seal, the moisture will go right up into the ceiling cavity. Finally, make sure that the fan runs for about 1/2 hour after anyone uses the shower. It takes about this amount of time to flush the moisture out of the bathroom.

      • Hi Ted,

        Thank you for the information. I need thing I forgot to mention, and this is really kicker, is that we don’t use that bathroom. It is a guest bathroom. I will buy the humidity sensor tomorrow and try what you recommended, however the home inspector did not detect any moisture.

        Are there any airborne particles or previous paints, or primers that could be causing this?

        We appreciate your help and expertise,
        Bala & Kim

      • Oh, that probably rules out that theory LOL. The test is likely unnecessary then.
        I’m baffled by how the odor could occur in one area and not others. Maybe one other possibility is that the air is particularly still in that one location so the fumes could build up. This is a stretch given your tests. Any other clues? Does the odor get better or worse at any particular time of day or year? or temperature? Any other information you can think of?

      • We haven’t been able to identify a pattern. I think your point about still air can be a contributing factor. We had one last thought yesterday.

        Can a cold air humidifier effect untreated wood, bed slats and compressed wood to cause this.

        Aside from that we believe the room is possessed!

      • Humidity definitely will bring out smells. So it would be worth trying without the humidifier and seeing if that makes any difference. During the winter the air is drier too so not using a humidifier and just the natural low humidity will be a good test to see if the problem is related to humidity issues

  6. Hi!

    Hopefully you’re still checking this site, because I have a mysterious smell that we cannot pin down. Our house was a 1925 bungalow that was taken down to studs and remodeled, then added on in 2014 – when we bought it from the builder. Our semi-attached garage (there is a covered open patio from the back door to the garage and the master bed/bath is built on top of the garage) faces an alley – when we moved in, the alley would basically turn into a mud pit, and we constantly had mud in the garage. We eventually had someone put in crushed limestone so we no longer have that issue. The garage now has a strong smell like dirt/fertilizer, even though no fertilizer is stored in there.

    When we are in the house, we dont really smell anything, but our clothes, shoes, cars (strongly), and luggage/handbags have a smell that we notice – something like musty or in the realm of cigarette smoke, but not that exact smell.

    We’ve had a mold air test – the only thing that came back was lower levels of the mold that was found in the outside samples. We had some water intrusion but that has all been replaced. There is no visual evidence of mold and that’s not really what we’re smelling. We had an air duct cleaner come look and say we didnt need a cleaning – he just ran some fogger to try and address it (it didnt). We have a drain in the laundry room floor that we poured vinegar and bleach down (at separate times) – but that room doesnt smell) We had Serv Pro come out and they smelled something in the garage and a little in the house. He thought it smelled like a weird chemical? They offered to clean the garage out, seal the concrete floor and do an ozone treatment.

    Any ideas?? We’re thinking we do the ServPro treatment or call a different air quality tester for VOCs?

    • Is it possible that the mud and water got into the garage walls? That would certainly leave a rank residual odor that would be hard to eliminate without cutting back the walls, cleaning them out and refinishing them. This is standard operating procedure when homes have water damage.
      It’s certainly easy to cut back the drywall in one location to inspect inside. I’d give that a look.

      • Hi! Thanks for the quick response. Perhaps i exaggerated the mud intrusion – it was really only on the floor – it definitely did not touch the dry wall. It would be in big cakey clods around the tires of our cars. then it would dry and we’d sweep it out. So the thought is that the concrete is harboring all of that? There’s also some dirt still on the floor of the garage. We never properly cleaned it.

        I will say the soles of my shoes have the smell. it just seems crazy to me that it would pervade our clothes and my purse, etc. We definitely do track some of it in the house.

      • Ok, it probably is the mud on the floor if those are the symptoms. I’d certainly try to wash the floor until it comes clean. Start dry with a shop vac or just a broom and dust pan. After all the visible dirt is clean, then try wet cleaning. I’ve used a carpet /floor cleaner for this as it minimizes over-spray. You’ll be amazed at how much dirt it will pick up!

  7. Dear Ted,

    We bought a manufactured home recently. It had a bit of a “doggy smell” and we thought it was just the carpets….had them cleaned. Didn’t help. Upon further investigation, we realize the “dog poop smell” is coming from the heating vents in the floor. It is especially strong in one bedroom and the living room. The furnace itself sometimes has the odor too. What could it be, and what should we do? It is not a musty smell, nor a “dead rat” smell. Smells like dog poop. The vents look very clean.

    thanks for your help


    • Well Deb, that’s a new one! Is it possible that the system is picking up the odor from outside? Sometimes the ducts run under the house and if they have air leaks (which they all do) it will suck in smells and distribute them around the house.
      Since there aren’t many things that have that distinct odor, I’m ruling out the standard mold or dead animals. So start outside and see if you can detect the same smell anywhere outside around the house.

  8. Hi Ted, I wonder if you can help? We have recently had a garage conversion and noticed that over the last three weeks the smell in the new room is so strong that we can’t use it at all. The smell is just like gas/eggs. It doesn’t change if we have the heating on or off. We have tried venting the room for 48+ hours but the smell only returns. We have had a plumber round to check if we have a gas leak and he has confirmed that we do not. We do have a water pipe that is accessible but no gas mains.
    Do you have any idea what this smell could be or what action we should take to get to the bottom of it?
    Thank you

  9. Hoping you can help with some advice. Our house is 10 yrs old and I started to notice a musty/ moldy air coming out of the vents a few months ago regardless of whether it’s the AC, heating or the fan that is on. The smell is incredibly intense in the HVAC room. Had the ducts cleaned two weeks ago. They didn’t find anything other than the usual dust buildup. The smell became even more intense after the duct cleaning. The AC evaporator coils and the enitire AC unit were checked, no mold or buildup. I also had a mold inspection done last week and the inspector found no mold. attic was also checked and there was no smell there. The humidifier filter was changed after the duct cleaning and it had that awful smell. I’ve had the windows open for the last week and turned off the hvac to see if things got better, however even when the system is off there is still musty air coming out of the return air vents. Gets a lot worse on rainy, damp days. Don’t know what to do next. Please help! Who can I call to inspect this further?

    • It sounds like you’ve been quite thorough. Since you discovered that the humidifier filter had the odor, it sounds like that was the culprit. This is often the case. These central humidifier systems are ideal breeding grounds for unwanted biological organisms. Any place that stays humid, especially warm and humid, will breed growth of these things.
      I would disable the humidifier – in most homes, these are unnecessary and can do more harm than good. During the winter, if you need some added humidity in the air, use a smaller room humidifier and only humidify the areas where you need it, like in the bedroom while you sleep.
      As for eliminating the odors, someone should thoroughly clean the humidifier and the areas of the system directly connected to it. This can be difficult because of access, but from your description, this is very likely the source of the problem.
      While the weather is mild, I’d keep airing out the house and keep the AC fan turned on to help flush fresh air through the system. Much better to do that now than when it’s cold and the house is sealed up for the winter.
      Note that it is also quite possible that there is an air leak in the duct system that would pull in foul air from somewhere else in the house. For example, ducts often run through the basement. Unfortunately, these types of leaks can be difficult to find and it can be hard to find a contractor who has the equipment necessary to locate these leaks.
      When I’ve done this type of work, I’ve used a theatrical fog machine to create “smoke” that is blown into the system, after sealing the system up. Then the smoke seeps out of leaks, making them much easier to locate.
      The type of person you want to look for is probably an energy auditor that specializes in home troubleshooting. You may have to talk to a number of them before you find one that can help you. But they’ll have the equipment and training to track this type of problem, even though it isn’t strictly energy related.
      Good luck. These types of problems are very frustrating but I’d definitely start at the humidifier.

  10. I hope that you still check this because I need advice! We just rented an older (1950s) home that has a strong ammonia-like odor underneath the kitchen sink. I can also smell the smell but not quite as strongly in the dishwasher directly next to the under-sink cupboard. My immediate impression was that the previous tenants kept a cat litter box under there or something. I called the gas company to make sure it wasn’t a gas leak as I’d read online it could be, and the tech said there is definitely methane present in that cupboard that he was picking up on his detector but no dangerous gas levels. He was perplexed and said it could be a small leak in the gas pipe that runs behind that sink (and outside for BBQ hookup on the opposite side of the wall) but to him it doesn’t smell like natural gas. He thinks it is probably something under the house or under the base board of the sink cupboard. There was a large bulge in the wood of the bottom board, and he cut into it to check the gas level inside. A lot of bright almost lime green sawdust type stuff came out, and he said the wood is rotten/has been exposed to moisture but he has no idea why it would be that color and he’s never seen any wood that color green before. Do you think we could have mice or rats living under there? I haven’t seen any droppings yet or anything. Or do you think the cat box is the most likely explanation? Or could it be a small gas leak that smells like cat urine for some reason? Or could it be sewer or drain issues? Or dry rot? I’m so confused but it smells really gross and makes me not want to cook in the kitchen. The landlord is sending a contractor to take a look at it tomorrow. Should I also call an exterminator in?


    • Quite often the ammonia odors are urine related (mice are particularly stinky). However, the lack of droppings makes me think that it’s something else. We get field mice in our house and they leave droppings everywhere!

      Sewer gas smells, in my experience, are usually different from ammonia smells. However, the methane detected could be related to sewer gas if the drains aren’t vented properly. But again, if they were high level, it would smell different. I say usually because there can be an ammonia smell from them so I wouldn’t rule it out.

      Do you notice any active moisture under the sink? That is, is the wood damp? Odors are often released by moisture. that wouldn’t be the cause necessarily, but it can make the smells worse.

      There are also some electrical smells that can be ammonia-like. Is there anything electrical under the sink that could be heating up and emitting the odor? This is a long-shot but worth checking.

      Another consideration is that some older building materials contain formaldehyde. This can be released when the wood/material gets wet and/or rots. Given your description of the mysterious rotten wood, I would most certainly investigate that closely. Since it’s rotten, break off a small chunk and sniff it to see if that’s the source of the odor. I know it’s nasty, but you need to determine if it’s the source. If it is, then the owner should have a contractor cut out the affected wood and replace it. Here a discussion of this type of issue on another site.

      I can’t explain the dishwasher smelling like that. More likely than inside the dishwasher is under or behind it is the source of the odor. If the odor is generated by rotting wood in one area, then it certainly could be the same thing in another.

      Hope that helps. If you discover the problem, please post your solution. I’m sure you Googled around for a solution and found that a lot of people are plagued by this issue. Learning your solution would help countless others suffering the same problem.

  11. can you tell me about my air duck that’s in the attic. I have rats up there right now, and have closed all the entry points that we know of, there are traps up there now, we have caught 3 so far, i hear more noises at night, but they just don’t go to traps.

    There were holes found in the duck work and my exterminator taped them up, but insists they were not caused by the rats.. I live in las vegas… Can you just replace the area that was ripped. they were ripped as a slit not hole by the way. I already know I would need to clean them after everything is done. As well as the rats have to be all caught first.

    I don’t want to be ripped off by some company telling me I need to replace everything. There 12years old by the way, when the house was built.


    • Assuming you have “flex duct”, it’s easy for someone to replace a torn segment. You don’t want to patch it typically because it should be a multi-layer duct, with plastic on the inside, then insulation, then more plastic. You want to replace the length from the place that it connects to the register in your ceiling to the main distribution plenum.
      Here’s a link to flex duct to give you an idea.

      An alternative is to cut the duct at the slice and join it using a piece as shown in this photo.
      Connecting two pieces of flex duct

      In general, this should be very routine work to fix. It shouldn’t cost more than a couple hundred dollars, most of that in labor costs for someone to spend a couple hours crawling in your 150 degree attic.

      Good luck. Feel free to ask more if you’ve got a different configuration. But overall, it should be easy to repair properly.

  12. We have had temps in the 90s and hot for awhile, I can smell something that to me could be hot, wet insulation, is that possible? I don’t know how old the roof is and it looks pretty good. This smell is a hot moldy smell. Makes my nose hurt. 😉

    • You might want to check underneath your living space like a basement or crawlspace. They often get humid and smelly in the summertime and the odors tend to rise up into a living space. Usually smells from the attic don’t come down into the house unless there’s ductwork or the air conditioning system up there and then those others can get sucked in and distributed around the house. But I would definitely check below the house first.

      • Thank you so much, earlier this year we had a problem with some water in our crawl space. I thought we had gotten it taken care of. I will start there. Thanks

  13. We moved into a house in 2009 which was built in 2006 and sat empty. We have a musty smell you can smell when you walk in and then when we leave the house we smell. We have changed a/c, painted which was what the indoor air quality told us to do. We are thinking about replacin our cellulose insulation. Could this be the problem?

    • When you say you changed the a/c, what do you mean? Did you replace the entire system, the ductwork or the filter?

      Mustiness can some from a variety of sources but typically, you will find it associated with moisture, often starting in the basement or crawlspace. Do you have a basement? If so, what is it’s condition? Is it dry or wet? Do you have a crawlspace under the house? Does it have a concrete floor or a dirt floor?

      How about your ductwork – does it run through areas of the house that might be musty like the basement, crawlspace or attic? Ducts often pick up smells when they’re not sealed air-tight, which most are not. It’s definitely something to check. Also the blower unit (called an air handler) – if that’s located in the basement or attic, it very likely sucks in a considerable amount of smells from the area where it’s located.

      Unfortunately, the best way to determine the location of odors like this is to investigate the nasty bits of your home. When I would consult with clients, I spent most of my time crawling around in the dirty, damp, cob-webby spaces since they’re the source of 80% of the problems I found.

      Since the house was built in 2006, it’s probably fairly tight. If the house is closed up much of the year due to heating or cooling, then it may get insufficient fresh air, so even a relatively clean house can end up smelling musty. I highly recommend fresh a air ventilator, called HRV (heat recovery ventilator) or ERV (energy recovery ventilator). Once you’ve lived with one of these for a while, you’ll wonder how you ever got on without it! In the meantime, you can get a similar (though highly inferior) effect by leaving a bath fan on round the clock. This will slowly flush out the air from the house. The downside of this method is that you don’t know where the “fresh” air is coming from. With an HRV, the air inlet is known to be a location outside the house where there’s good air. When you run a bath fan, the air that seeps into the house will come from anywhere it can leak in such as through the attic or basement which probably have odors of their own. You can mitigate this by cracking a window, approximately 1″, on the opposite side of the house as the bath fan. This will tend to draw fresh air through the house in a more controlled manner. See this article for more information on HRVs and ERVs.

      In any case, I recommend airing the house by opening many windows and doors whenever the weather is good and you don’t have to run the air conditioner. This will help flush out the stale air. And definitely search high and low in the house (attic and basement) for sources of the odor. I wouldn’t jump to conclusion about the cellulose insulation – usually that doesn’t cause this type of smell, especially in a new house. Cellulose is one of the better insulation products so you’d probably be wasting your money by replacing it.

  14. Pingback: What Does Structurally Unsound Mean | Razeeti3

  15. Thank you for this article-it is very helpful. We recently purchased a home to renovate (not currently living in it). It has a detached garage with guest quarters over it. When we bought the home that guest area had a musty, urine-like odor. The contractors we interviewed at the site all said it would go away once we tore up carpet, put up drywall, painted, laid down flooring etc. Well, ceiling (popcorn) was torn out and replaced, rug pulled up, drywall placed and it still stinks. It does seem to come from the area where the bathroom is, but we completely changed the footprint so all pipes were moved, etc. I am worried that it is still going to be there after floors and paint. There is no central air/heat, and generally poor ventilation so I have no doubt that is adding to the problem. There are two large windows so we’ll start leaving those open with the screens in once this rain stops and see if that helps. I had a pest control person come by today and they said there was no evidence of rodent or other infestation and it didn’t smell like a dead animal to them. The water heater is in the garage-is there anything with that you can think of?

    Thanks in advance 🙂

    • Sounds like you have been pretty thorough. The most common sources are animals urinating and wet/rotten building materials. I still would not rule these out. But, since it’s near the bathroom, there’s a likelihood that it is seepage that got into the wood sub floor. Though if you’ve replaced/moved the plumbing, you would think that someone would have found a problem.
      Is there an air distribution system in the house? i. e. for central air conditioning? I’ve found mice living in these areas before and that causes exactly this smell. Mice are really nasty.
      Even though they didn’t find signs of problems, you might set out a bunch of mouse traps and see if you get anything or even if the bait gets eaten.
      If you can think of any other information, please share and we’ll try to get to the bottom of this!

  16. My problem is that whenever we enter our house from outside, we get a very dusty/musty weird smell – not the moldy kind. Once we are in we (both my husband and I) no longer smell it. Our sense of smell seems to get “used” to it. I moved in a few months ago and the house had not been “really” lived in for a couple of years.I learned that the owner was coming in once in a while. I had the vents cleaned, tested for mold, done mold remediation, cleaned carpets. We are controlling basement humidity using a dehumidifier. Thought it is nearly 24 years old, it is a really tight/sealed house. The garage does have an odor – best way I can describe it is lingering old burnt tires . The garage is quasi empty. I am wondering if I need to have a ventilation installed in my attic. I am not at all savvy about these things and wanted to understand this a bit more before I talk to an HVAC person.
    Thank you for this site T.D.

    • Yep – your nose gets used to smells fast. I was just thinking that after having been away from my own home for a weekend. Came back and pew, it didn’t smell fresh at all! I’ve got a whole-house ventilator that’s been on the fritz for a while but I strongly recommend either HRV (heat recovery ventilator) or ERV (energy recovery ventilator) installation in any tight home. Once you’ve used one, you don’t want to go back – the air is just that much fresher with a steady, albeit small, supply of fresh air.
      You asked specifically about attic ventilation – I’m not a fan of attic / roof fans (no pun intended). A study was done that showed that attic ventilation leads to greater energy use in the house and can create some problems.
      If you talk with an HVAC contractor, ask about HRV’s or ERV’s. If they give you a blank stare, find another one! Any reputable contractor should know about them.
      One word of warning – they can be tricky to install properly. There are different theories but most HVAC installers will just connect them to your air conditioner ducting. This is less than perfect because it forces two different fan systems to work against each other and the air conditioner has a fan that’s 20x as powerful as the one in the ventilator which can totally disrupt the proper operation. My preference (and what I did in my own home) is to install a small, dedicated duct system for the ventilator. Pull stale air from the rooms that need it the most and supply fresh air somewhere nearby but far enough away that the air can flow through the house a little and doesn’t just get sucked back into the ventilator input.
      Hope that makes sense.

    • Dry drains . Pour water down your drains once a month & flush all toilets. Sewer gas! Or dry drains can cause odor you describe.

  17. We’ve had this weird smell in our house and we can’t figure out what the heck it is! I don’t know how to describe it except that it’s a very stale, old, dusty, sometimes dog poop type smell. Not sure if I would describe it as musty. Maybe slightly. We do have a crawl space with insulation that has fallen off the walls and it’s pretty dirty and nasty. It’s right below our living room, which is the area that smells the most. There’s also a main level bedroom that remains closed usually and that room really smells. I’ve cleaned EVERYTHING, changed the furnace filter, and even cleaned the carpets. Could the old insulation the basement crawl space be causing the smell? I can’t think of what it could be and it’s driving me nuts! No water issues that I can find, and no concentrated areas of smell. Just in the whole room.

    • It sounds like you’re on to something since the crawl space is under the living room. Air, and odors, tend to travel up through the house, so it’s likely that any odor starting in the crawl space would move up into the living room. The question is – what does it smell like in the crawl space? If the odor starts there, it should be strongest there.
      It’s pretty common for odors to be most noticeable in the winter when the house is closed up and you don’t get much fresh air.

      One thing that I get in my house every winter are mice. They’ll come in from the cold and invariably one will die and rot and make my house stink with a nasty odor. While they’re alive, they’re gross and will pee on things causing some odors. But it’s their death that really stinks.

      When you’re lucky, you find them, but often, they crawl into tight spaces to die. I’ve had them under my fridge, in boxes, underneath cabinets, inside walls and ventilation ducts – it’s awful! When my parents moved into their new home, there was a family of mice living inside the furnace! It wasn’t until I was inspecting it that I pulled out the filter to find all the rotten little bodies. You can imagine what the house smelled like!

      So that’s my best guess for now since you don’t seem to find any moisture problems that could be causing mold to grow and make the house musty.

      You might want to have a pest company come in and look for mice and or dead bodies. If it is that, they’ll recognize the smell immediately, which at least would be helpful in figuring out what’s happening. If they tell you it doesn’t smell like a dead mouse, then it’s worth pursuing other things, but that’s a good starting point.

  18. I have an odor which accumulates in my kitchen and hallway typically when there is no activity in the house It smells like a candle wick has just been blown out. Any ideas on what this smell could be? It seems that it’s worse now that the windows are closed up, of course.

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