In a well-kept stick-built home built 1930's-40's that had some stagnant water in hand-dug basement go undetected for some time (I know not how long that's why it was undetected!) is it possible/likely/probably that a mildew smell would infect antique wood furniture in a carpeted room on the second floor of said home? Entire home was carpeted, no water came or flooded to 1st story. Only basement. Door to basement is one exterior access and one interior access. The interior access door is on a 1-sty section of the home that does not sit below the second story with the furniture.

Mildew and mildew smell are 2 different things. Yes, mildew spores can be carried through the air handler. However, if it is just furniture and nothing else, doubt it's mildew as it would also be in the carpet and on wall surfaces.

So what smells like mildew but isn't mildew?

Mildew is the actual spore, a grey or black looking substance. Other substances have a very similar smell but are not mildew. As I noted, if it is only on 1 item, furniture and not walls or rugs, books etc, it may not be mildew. Can you see any spore growth? If it is mildew, you may have similar growth in the ductwork from the basement, assuming such exists. If you don't have any heater or airflow from the basement then I would not suspect mildew growth from that source. Mildew can come from anywhere, outside or inside.

I truly appreciate your assistance here, ma0641, I guess I should qualify that this home has radiators, no AC and there would be no duct work per se. I do not see visible mildew on the furniture. An auctioneer is devaluing these pieces saying there is a mildew smell from the stagnant water from the basement. There is also only one bathroom and kitchen (sources of damp) and they, too are both downstairs in the 1-sty part of home that is not below 2nd story. In your experience (and in my shallow experience) I am thinking there has to be a moisture somewhere near this furniture, no? Otherwise, what could he be smelling--what are those other substances you refer to? The furniture has not left the home in about 70 years. My windows show no signs of mildew in double hung windows. I will say it's been a long time since we had new carpet. It was last put in in the 1980's. But, as I said, it is a well-kept home. No kids or pets. We do use coal fire for heat.

There is no air flow through the house if you have radiators and no AC. Plus, you mention that the furniture hasn't been moved for 70 years. Over the years, dust, bug droppings, household odors penetrate the wood and are trapped in the finish. Quite honestly, I would expect such smells. However, I would take a diluted bleach solution, 1:3 and use a slightly damp rag to wipe all the parts of the furniture. Open the windows and use a fan to move some air around. What you are smelling is quite common under the circumstances you note. You will not damage the furniture if you use a diluted solution and only a slightly damp, not wet, rag. Then, after a couple of days, apply a light coat of furniture wax. Let us know how this works to remove the smell.