I dont know the answer to your question, but, I will suggest, you open your windows often for fresh air. All houses need fresh air. I open windows every single day. Not all of them, most days, but, I leave my exterior doors open all day long, when I am home, and have the storm open to the screen all day long. It gives a nice cross breeze.

I might suggest though, that you get your air in the house tested to make sure that it isnt something that can be detrimental to your health.

It seems to happen during shifts in humidity.

Does the house have AC?

It sounds like a case of dirty sock syndrome. (*IF* that's what it is the smell is from bacteria on the evaporator coil was coined dirty sock because the smell is similar to a gym locker room.)

The house was built in 1929, which back in that day -- there was no air conditioning.

Chemical cleaning the evaporator coil, should at least let you know if that is it or not. But if your habits (among others) don't change (how you operate & maintain the HVAC system) the smell will return in time.

There are other more costly methods to deal with it... some of which may work for awhile, may not last for long.

Google search 'air conditioning dirty sock syndrome' it should be noted that Trane coined the phrase but all manufacturers have had bouts of this kind of trouble.

It should also be noted I am not psychic, I would starve as a fortune teller... this is 'merely' what it sounds like to me. If you're not testing -- you're guessing. Tests cost money.

Dirty sock syndrome is rare. When it does occur, it's typically in the spring or fall when an air conditioner has been out of service allowing stuff to grow on the evaporator coil which is then disbursed when the air conditioner or furnace is activated. The OP relates the problem also occurs in winter, so it's likely there's another root cause.

A home built in 1929 has had plenty of opportunity for mold/mildew to become well established indoors: in framing cavities, in basements, and in crawl spaces. Molds and mildews do well within the same temperature range that we humans find comfortable. Their activity correlates with relative humidity and they can be turned "on" when indoor relative humidity is high and "off" when it's low.

I suggest a thorough inspection to identify areas where mold/mildew may be present and remediation as needed. Maintaining indoor relative humidity less than 50% should control mold/mildew growth. That may require integrating a dehumidifier into the HVAC system or it may be required only in a basement or crawl space. Venting point sources of moisture such as cooktops or ranges and bathrooms is a good preventive measure. If the smell persists, the OP may wish to consider an active treatment system such as Lennox's Pureair system https://www.lennox.com/products/indoor-air-quality/air-purification/pureair?rev=BVSpotlights

Thank you! We’ve had our house tested 7 times for mold. 7!! We had a small amount in thr basement (remediated) and Hurricane Ida added some to our AC units (also remediated). I’m practicaly a mold expert at this point, honestly. We did swab testint behind an electrical outlet which was negative (plus endless air tests, etc etc). . i do wonder about wall cavities but not so easy to test with plaster walls. we are considering it tho!

it doesnt smell anything like a dirty sock. i do know that smell well. its more like…fragrant wood. almost like burnint incense only its not a burnt smell (that would have me calling thr fire dept).

we keep humidity under 50%, have a dehumidier im basement running 24/7. im considering a whole house dehumidifier tho that wouldnt solve this per se.

we have central air AC, and hot water boiler badeboards for heat in winter.

I would definitely consider a system like the Lennox Pureair system (I had two in my former home.) It can be integrated into the air conditioning system for summertime operation. In the winter, you can run the air conditioning system in "fan only" mode to circulate air for treatment.

it doesnt smell anything like a dirty sock. i do know that smell well. its more like…fragrant wood. almost like burnint incense only its not a burnt smell (that would have me calling thr fire dept).

house fire at some point in past? Usually in the event of a house fire encapsulation of smoke damaged furnishings is performed of those furnishings that are merely smoke damaged. Maybe a poor encapsulation / house flip of some kind?

It's only an educated guess. You bought the house 5 years ago. Who remodeled it? (assuming it was remodeled before you bought it.)

House flips are notorious for similar or worse problems. Again I only know what you tell the board. Not a psychic bone / muscle in my body.

After we cleaned out our ductwork and coils last year we added an Aerus air scrubber to the ductwork. We do now keep that running even in winter to help clean the air and maintain moisture. In summer (now) we have it on auto to run with the AC, and make sure humidity stays under 50% (if I run it continuously the humidity gets too high). We also have air purifiers in bedrooms and in kitchen. I went nuts making sure air was nice and clean!

This house never had a fire, the previous owners owned it for 30+ years and our neighbors still keep in touch with them. We’ve even seen them at BBQs, so nothing shady occurred prior, to our knowledge. It wasn’t a flip, just outdated and we’ve done a ton of work to it. First thing we did was refinish the floors. I’ve been wondering if that had anything to do with this since the smell is everywhere! We weren’t thrilled with the job they did. Looks nice, but they left a mess. It was water based stain, if that matters.

I just walked around the house. The smell is everywhere, but not in the basement. My husband says he doesn’t really smell it, but last night agreed it was a little stuffy.

I also have issues in steam rooms, this reminds me of that though not nearly as intense obviously. I can’t stand steam rooms. And I can’t stand it after we brew coffee. Maybe it’s me!?! Lol

First thing we did was refinish the floors. I’ve been wondering if that had anything to do with this since the smell is everywhere! We weren’t thrilled with the job they did. Looks nice, but they left a mess. It was water based stain, if that matters.

I don't know it sounds peculiar.

For the record I don't believe air scrubbers do as they suggest. They are often put in / but in my experience do nothing more than add additional maintenance expenses. If you don't maintain them in as little as a year or two, they do nothing. The gadget market is a billion dollar market full of possibilities of spending money. Treating a symptom versus finding it and actually fixing it? It's only joy is it's practically free some of the time. This isn't meant to bash your choices, just inform you that complicated problems often times require complicated solutions.

Maybe take up a piece of that floor from area you readily smell the smell put it in sealed container wait 30 days or so and take it to lab have the off gasing analyzed. It might be one way to eliminate the floor as a possibility. Contact the lab first to see how they prefer to recieve it.

I’ve thought about the off-gassing. It is a strange issue. It’s been here since we moved in! Only other thing I can think is the old cellulose insulation. I’ve smelled behind some outlets and can smell it, but it’s more like old paper (which makes sense since cellulose is basically crushed newspaper). I’ve had 3 professionals smell these outlets to rule out mold, which they have. They said it’s just old cellulose. Maybe I’m sensitive to it, and maybe moisture changes make it more potent. So weird! But it really bothers me.

Hi, Helpme,

At least one scientific study showed that the sense of smell isn't affected all that much by ambient temperature or relative humidity, so I doubt the slight increase in relative humidity from brewing coffee affects it in that way. That said, the aroma of coffee triggers chemoreceptors and it may trigger ones that detect mold/mildew odors.

Curing of floor finishes is generally complete within a couple of weeks, so I doubt off-gassing of VOCs is the root cause. Where off-gassing occurs, most people describe a chemical-like odor not a musty/moldy odor.

Cellulose insulation will adsorb and desorb moisture depending on the temperature and relative humidity. Maintaining 50% r.h. in your home doesn't guarantee the relative humidity in wall cavities is at or below that level. Indeed, the relative humidity in wall cavities can be higher as a consequence of indoor air entering the cavities in winter and cooling. Ditto for outdoor air entering the cavities in summer. Those conditions may be favorable for mold/mildew growth. While most cellulose insulation today is treated with borates to minimize the potential for mold/mildew, older insulation was not. Air sealing to control infiltration and exfiltration would be helpful, but probably cost prohibitive in an older home.

One thing you might consider with regard to improving air quality is a fresh air ventilation system such as a heat-recovery ventilator or an energy-recovery ventilator. Either would reduce the concentration of indoor pollutants. It might not be the solution to your problem, but, in tandem with other measures would improve the indoor environment.

Wow! Thanks for that insight, super interesting about the smell receptors. We often joke that my super hero power is sense of smell!

In one of the many mold tests we’ve done, I used an Industrial Hygienist. They spent hours in the house with a moisture meter. While moisture levels were indeed higher behind the plaster walls, they were not flagged as concerning. They said that’s common based on materials and also said they’ve never found mold behind plaster walls.

I do still wonder if there is mold in these air cavities! But with this issue, it’s literally everywhere. I even smell it/sense it in spaces where we added extensions to the house and it’s drywall. So if it was mold I was smelling, it’s literally covering every wall everywhere (except the basement where I don’t smell it!).

Another project we did when we moved in was re-sided the house. We didn’t replace any insulation. I wonder if that had anything to do with this too.

I will look into the ventilation system for sure. Thanks for the tip!

The conditions in wall cavities, and in the cellulose insulation, are not a constant. Any sampling is a single measurement at a single point in time.

This is probably of no help since yours is through the whole house, but could there be a leak somewhere? Prior to moving into ours, there was one room that had a musty smell to me, especially near the window. Floors were being replaced & pulled up, so nothing unusual looking revealed there. Flooring people recommended a contractor to come look, he never called me back, so nothing further came of checking it out. Fast forward several years and a leak developed on the ceiling downstairs— turns out it was coming from near that upstairs dormer window even though that room didn’t show any signs of a leak. Flashing was missing, most likely from a roof replacement after tornados years prior. Since you mention hurricane repair, makes me wonder if it couldn’t be something similar.

Thank you! That’s helpful to hear your experience. We had water in the basement during Ida, and another random leak near that time (all repaired). This issue has been ongoing since well before then. I literally just aired out the house all morning because humidity is low today, smell is still here! Now I’m running the AC to see if that makes a difference.

probably you have plaster walls, in the twenties they sometimes used horsehair in with the plaster.. I have a house in new england that is rental apartments - sometimes when the air is still its you can small a sort of musty smell. my grandma said it was horse hair.

Is it possible the previous owners were pipe or cigar smokers and the smell has permeated parts of the house and the change in humidity releases the scent?

I would be really surprised if ventilation helps a 1929 era built house. Those houses already tend to be drafty! Unless the renovation work really tightened things up?

If you don't find the source --- I think you're setting yourself up for disappointment. You need to find the source IMHO.

While drafty homes are ventilated by definition, air infiltration occurs at an uncontrolled flow rate. It also passes through wall cavities where it can pick up accumulated allergens, dust, molds, insulation fibers, etc. By contrast, a fresh air ventilation system provides a controlled ventilation rate with air that is outdoor air-- uncontaminated by whatever may be behind the walls.

This is all very helpful. Regarding smoking with past owners, I don’t think so. I grew up with parents that smoked, I’m very sensitive to that too and it’s not like that. It’s more like a wood or maybe even dust type of smell, but it makes the air stuffy feeling. It’s so bizarre. It’s still in the house after airing out yesterday. We also have several room air purifiers and the air scrubber in the ducts and it’s still around, which makes me think it’s something with the wood house framing, the insulation, or the wood flooring?? Ugh

Here’s a wild idea. Since I’m also smelling it when we brew coffee, I’ve wondered about our water quality. We have a Halo5 whole house water purification system, but maybe it’s still hard water (haven’t had it tested). Maybe something with the pipes in the house during humidity shifts?? I probably sound like a crazy person but I really want to figure it out.

I have a guy coming to air test our wall cavities this week, maybe that will give us some clues!!

Cold water piping could play a role. The surface temperature of uninsulated pipes may be below the dewpoint temperature when outdoor relative humidity is high. The resulting condensation on the surface of the pipe could create favorable conditions for mold growth. That may occur in summer, but I would not expect it in winter.

Brew your coffee with bottled water from the store. Note any changes.

If there's a difference then get your house water tested.

We also have several room air purifiers and the air scrubber in the ducts

Maybe the odor is coming from one or more of those air cleaning gizmos? Try shutting all of them down, get some fresh outdoor air in the house?

The reason that I'm suggesting this is because, many years ago, I bought an ozone generating 'air cleaner' and the smell that emanated from it was funky.

If you haven't already done a survey of the walls with an infrared camera, I suggest you do so. They are great tools for finding missing insulation, air leakage, roof leaks and plumbing leaks. You can purchase one that works in conjunction with your cell phone for a couple hundred dollars. It's one of the best tools in my bag.

What type of clothes dryer do you have? Vented or ventless? Gas/ electric/ condensing/ heat pump?

Another suggestion--Invest in a moisture meter and probe around all of the windows or do as Chas suggested ^^ with an infrared camera.

The issue was around prior to all the air purifiers. Great suggestion for infrared camera!! I’ll look into that. Regarding the dryer…it’s gas powered. I have no idea about the ventilation! However, we were doing loads of laundry the other day when the smell came out and I literally made a note of it to track when it happens!! Maybe that’s the connection??

Ok so dryer is center to exterior…not sure about the condensing heat pump? Any guidance there for me to check out?

Dryer is vented* to exterior. (Sorry autocorrect!) Got it cleaned this past January.

Maybe dont use the dryer for a while and see if the odor comes back. Do you have clothes lines, you can hang clothes on. You were also using the washing machine, maybe the odor is from that. Do you have a front loader washer?

Top loading washer that I clean religiously and I use a laundry additive to keep mold away (EC3 it’s called from Microbalance) and I do tub cleans frequently with it. Washer is good. We didn’t use the dryer yesterday at all, and smell/stuffiness is still here. The AC hasn’t been pumping as much bc the temp has been cooler here. Wondering if that plays into it…?

Some older homes have a definite smell….my husband said his grandparents’ farmhouse had it….generations of smokers! But yes, you appear to have a superpower!

OK, so that means no odor coming from the dryer. But the dryer is drawing air from inside the house and thru any cracks and crevices where the odors might be.

We have an air pipe installed in our house. That will help. Try that. Air purifier will help.

That^ and the house is almost a century old. So it is leaky. There may be layers of hidden old wallpaper and who knows what all else that are just smelling 'old'.

FWIW, pigmented shellac is the go-to to seal in odor should you discover the source and the source is paintable if not removable. Zinsser's BIN with the red label.

One more wild idea for you--post the size of your furnace, AC unit, and air handler for the pros here to evaluate. My husband was smelling a "hot" smell for months during a winter a few years ago. It turned out our air handler was undersized for the furnace, and he was smelling a motor overheating. I wonder if humidity swings are stressing your HVAC equipment. And maybe the similar coffee smell is the machine components getting hot.