Bad Odor

From an inspection I did approx 2 years ago the client is getting what he describes as a dead fish odor coming from the master bathroom and bedroom when the air handler is running. The contractor was concerned about chinese drywall and we tested a sample but negative and no corrosion was noted either. The odor has been getting worse with the temperature rising and the client’s son has asthma which is getting worse. I have not detected the odor but the contractor describes it as wet insulation odor but we can’t find any moisture or wet insulation. Any ideas.

3,435 jokes have just run through my mind…the least crude of which being a blind man walking past an open Fish Market, tipping his hat and saying “Good morning, ladies”…

Contact an environmental specialist or industrial hygienist. Running a TO-15 test for VOC’s will likely pinpoint the odor it’s source.


Are there any plumbing vents improperly terminating in the attic above these areas or near the air handler?

Are there any air admittance valves located inside the bathroom?

Does the A/C unit’s condensate line improperly connect to a plumbing vent?

Maybe a mouse or squirrel got into the air handler, any signs of pest intrusion?


Check for build up in the drain pan of the evaportor Inside the air handler, or if there is a humidifer .

Where ever there is moisture there will be odors. You my need a thermographers help.

Foul odors can come form any number of things in an HVAC system. Could be anything from a dead mouse, microbial growth, chemical offgassing, or poor venting. You could spend hours looking for the cause without any results. I ususally would recommend doing some sort of testing to help narrow down what you should be looking for on an inspection. Testing will tell you if you should be looking for something decaying in a duct, sewer gases being drawn into the system from a poorly placed vent, mold or bacteria growth, or adhesives that may be giving off fumes. It could also be a combination of different problems causing a strong smell. It can be a pretty expensive endevour to hunt down a decaying mouse in duct work if it is not readily visible. Don’t needlessy waist your client’s money and your time trying to figure it out by poke and hope inspection methodology. Teting will also verify that a substancial effort was made to identify the source and can also be done once the problem is found to verify the problem has been solved.

Think of it this way, your doctor wouldn’t give you certain kinds of medication without knowing what is going on in your bloodwork first and then monitoring it to make sure it is doing it’s job. Anytime there is an IAQ complaint, you have to treat it as if someone’s health depends on the outcome…because it does. If you are going to take those kinds of inspections, follow what is considered to be acceptable industry standards to document and diagnose the issue. Verify the problem has been solved afterwards and recommend they seek the care of a medical professional since there is obviously an effect on someone’s health in this issue.

FYI: Mold testing can detect dead animals such as rats in most cases. There are certain molds that grow on a decaying carcasses.