For the past month (before we even turned the heat on) my daughter's bedroom has had a terrible smell like moldy plastic. It is not a sewer smell or dead animal smell, we've experienced those. First we took the furniture out, and steam cleaned the carpet which is only 2 years old and showed no signs of stains. Smell continued so we ripped the carpet out. We had a friend check it for mold with a moisture meter. No moisture. We had our insurance company send out an inspector and he couldn't figure it out. We think we've found where the smell is coming from. The house is on a slab so the copper pipe that leads to the baseboard heat comes out of a hole in the slab which is slightly wider than the heating pipe to allow for expansion. The smell seems to be coming from there. And in the next room, the living room, around that heat pipe where it comes through the slab, the smell is there as well, but not as strong.We had our oil company repairman check the smell and he had no idea why it smelled. He checked our heating system's pressure to test for a leak and the pressure was fine, granted he was only here for about an hour. Next thing we plan on doing is shutting off the boiler and the water supply to it for a few days so the loop can't be automatically re-filled if there is a pinhole leak somewhere near the smell and then seeing if the pressure goes down. Additional info-Outside the bedroom is the cesspool vent. We have been in the house for 11 years and have never had this smell. House is 20 years old. Any ideas what else could be causing this if it is not a leak or a better wy to determine if we have a leak? Thanks so much.

 

By all means, first verify if there is a leak in the hydronic system. (Hot-water heating systems will turn black and have a slightly musty odor - but not a "terrible smell".) If it's not leaking, then the odor must be coming from underground, up through the slab's hole for the copper pipe? Then, maybe you could seal the annular space around the pipe with silicon caulk.

Is there any chance the oil tank or piping is leaking?

You mention a cesspool and vent. In many areas, these are prohibited - but perhaps not where septic tanks don't work. What odor comes out the vent? (Well, maybe don't check that.) Could there be a leak in the cesspool?

 

With Haloween nearly here, this is fodder for a good scary story... lots of different scenarios come to a fertile imagination... Every 11 years, on Haloween eve...

I wonder though... if there were insulation under your slab... the foam stuff... if for some reason that it's 'breaking down' and releasing some 'gases' from the closed cells?

Has this year brought any unusual weather patterns that might have super-saturated the ground around and under your home? and now it's evaporating and the vapors are finding their way through the slab? Maybe there's some kind of mold growing down there?

The following idea is a little disturbing from a toxicity standpoint, but what about termite treatment? Has anything like that ever been done?

There are air quality companies that have equipment that can 'sniff' the air for a period of time and analyze the contaminants collected in the sniffer unit. I believe that this is the way your insurance company should be going with this. You should probably gently nudge them in that direction... I mean, what if there IS some toxicity there? This is probably something that shouldn't be left to linger...

Is your place built on an ancient Native American burial ground?