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bad smell from a new furnace

I hope someone can help us. I just read other info about stinky smells and new furnaces but this odor is a fishy smell...yes, it smells like really bad fish! Our new furnace/ac is only 6 months old. My old furnace-same ductwork-didnt make this smell. All summer the ac ran with no smell. The past 2 months here in Colorado I have been using the heat and about 5 times a day it happens. The smell will blow in to the house when the furnace kicks on a few minutes and then stop. Then the air blowing from the vents smells fine! Sometimes the smell hovers in the stairwell but then goes away when I open windows and doors. It is a smell that reminds me of a non-microwave plate that we burned in the microwave once, and also smells like the new glue we used on my daughter's baseboards/carpet when her space heater was on. I have checked (by smelling only) the washer/dryer, the sink and bathroom drains, the outside of the furnace (nothing), around the water heater, the fridge, the plastic around the can lights in the basement (it smells like stinky burning plastic to me-I know that sounds weird)
Our furnace is in the basement of our 900 sq ft up and 900 sq ft down 1950 house. It is supposed to pull in air from outside. It has a very expensive filter system to ELIMINATE ODORS! Our ducts were not new and seem pretty dirty to me when I look down into the room vents...but could this be the source of such a horrible smell? The first time I smelled it I was actually cooking salmon for dinner and for days after I thought it was from that. I cant imagine that furnace guys would use something that would smell bad when hot? If it was in the ducts wouldn't it smell bad all the time the furnace was blowing? Help! One of my babies is a baby and I am worried about her health. Any suggestions would be appreciated!

Re: bad smell from a new furnace

I just thought to mention that we had the house covered with stucco shortly after the furnace/ac was installed...and that the oven and fridge are new. Thanks for any input!

Re: bad smell from a new furnace


Something is wrong here, for sure.......IMO. Old unit didn't smell, but new one does. It's not unuusual for a new unit to give off "some" odor for the first few firings..... but 2 months of odor??? Something is amiss.

Virtually impossible to diagnose with any reliability from here. Couple thoughts though.......

Any chance that what you're smelling is a fuel leak? You didn't say what type of fuel this furnace is burning (LP or natural gas being the most likely), but folks often mistake raw fuel leak odors for other types of odors. If this is the source of what you're smelling......it's VERY serious and needs immediate attention. All the fuel piping joints should be properly & thoroughly checked for leaks.......including any new gas valves in the furnace itself. I've encountered several new gas control valves on both furnaces and gas water heaters that leaked just enough to cause what you describe.........and did.


Sometimes the installer or one of his helpers can place bags of "lunch leftovers" in a duct and "forget" about it.........knowingly....or unknowingly.

It's also possible (as mentioned) that you have a crack in your heat exchanger. This would allow exhaust/flue gases to enter the airstream to your heat ducts, but that crack may (more or less) close up once the HE heats up and expands. If you don't already have a quality carbon-monoxide detector......I'd seriously advise you get one......pronto. A Nighthawk digital (or better) would be my advice. (There are even more sensitive units on the market for more money, but you won't likely find them in a big-box.) Avoid all the cheapy units from other/lesser companies. Your life/health could be at stake. Nighthawk also offers combo CO and gas-detector units. That's what I'd truly recommend if you're going to get something "off the shelf".

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