Why does my central heater smell of urine?

December 25, 2012 10:11 AM

Whenever our high-efficiency heater runs, I smell urine. Why would that be?

Our house is a 1970's one-story ranch build on a concrete slab. We've owned it since August. The home inspector didn't see any signs of rodent activity, neither did the pest inspector, and we've had an exterminator out since then to spray for bugs and inspect once more. I'm pretty sure if we had sudden rodent activity, the cat and/or the dogs would be giving some kind of indication, wouldn't they? Also, we didn't have this trouble with the A/C, which we ran in the summer, this being New Mexico. We don't run the heater as often, this being New Mexico, but yeah, when we do, it reeks! We've changed the filter, and that didn't help. We've looked for pet accidents with a blue light around the air intake and found nothing. We've checked the carpeting all over the house and found no pet mistakes anywhere. My guy says that he smells "a little bit of something" but to me it stinks to high heaven.

The only difference between the summer and now is that the ceiling fans have been turned off because they need cleaning. Also, we had to replace the condensation pump (this was after the smell started) because the old one blew up all over the utility closet -- water everywhere!).

This could be unrelated, but since late fall, but I've developed a dry cough, ended up in the ER with said cough, and am now on an inhaled steroid (I have asthma).

posted by patheral to home & garden (6 answers total)

Are they fiberglas ducts? Some types of fiberglas and the resin used for glue will emit this kind of odor. Ammonia is one of the off-gassing ingredients, which is probably what you are smelling. It would be more evident with hot air than cold air. Possibly a duct-cleaning contractor can go through with a sealant spray. Some possibly relevant info.
posted by beagle at 11:03 AM on December 25, 2012

Is there a possibility that you have rodents in the ductwork itself?
The bedding and urine of the rodents remain long after the rodents are gone.

If the air conditioner uses the same ductwork as the heater, try turning on the air conditioner to see if the common ductwork is providing the odor. If the air conditioner in the winter does not produce the same odor as the heater in the winter, then the problem might be with the heater (the odor of rodent will be less pronounced with cold air, of course).

I know that odor. One time an empire of mice thrived under the upper intake manifold of the van. On a roadtrip, the odor of vaporizing mouse sewage and baking mice grew stronger and stronger and then weaker and weaker, disappearing entirely by evening. We found the hellish remains of their happy civilization on the post-trip investigation.

If you saw the same modulation in urine odor while you were operating your heater full blast (for a number of hours), you might check your ductwork.
posted by the Real Dan at 12:38 PM on December 25, 2012

My guess would be that it's related to the condensation pump, possibly something didn't get cleaned up after that mess, and you've got a mold issue, or there's still condensation pooling somewhere. My truck A/C has a similar issue - the drain has a bad habit of getting clogged, and when it does, it smells just like somebody took a leak in the vents for the first few minutes after I start the A/C.
posted by jferg at 3:53 PM on December 25, 2012

Here's a crazy, probably wrong guess:

When you're running the heater, does it smell around the base of one of your toilets? If you have a bad seal from your toilet's wax ring, perhaps the negative air pressure created by the heater's intake is drawing sewer gas into the house that would otherwise remain in place?

PS.: this sounds stupid but a similar thing happened at my house.
posted by zvs at 6:49 PM on December 25, 2012

Since I'm in the living room usually when I smell it, I'm guessing that it has to do with one or several particular ducts or a certain area of the house, but I really can't tell where or what would be causing it. We have three pets, and not a one of them is acting like there's varmints anywhere. We did check the toilets, as well as the closet, and all seemed well there. We had a tub of moisture remover in the closet for a while (and let me tell you, it was hard to find that stuff here in New Mexico) after the condenser incident and we soaked up the water pretty well with towels & junk, so I'm pretty sure we got all the moisture out. It's hard to keep anything wet here.
posted by patheral at 8:31 AM on December 26, 2012

Just in case anyone is curious, we had someone come check the place for critters and they found no sign of them anywhere. The smell is still there, but it's not critters. My honey still doesn't smell it as strongly as I do. He says he smells "something" while I'm coughing and hacking away.
posted by patheral at 11:06 PM on December 31, 2012