A homeowner turned to the internet for advice after being unable to detect the source of a foul, garbage-like odor that had permeated their home. Having only recently turned on their heat as the weather cooled, the homeowner thought the terrible smell might have something to do with their HVAC system. 

Here's what to know

The homeowner explained their situation in a Reddit post, writing that they had begun using their heat again for the fall and that it had run smoothly for the first two weeks. However, that's when the awful smell began to appear.

"We've been dealing with this for three weeks and going insane," the original poster wrote.

While acknowledging that they could pay for an HVAC specialist to come take a look, the prospect of spending hundreds of dollars on an inspection alone made the OP reluctant to book an HVAC visit. Instead, they turned to Reddit for suggestions. 

The OP further explained that they had already eliminated several potential causes. The OP inspected the furnace and did not find a gas leak (although, as commenters pointed out, a leak was still a possibility). They also changed the filter, which seemed to make the odor go away temporarily, but it soon returned. 

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What commenters said

While the OP had focused primarily on their heater as a potential cause of the smell, commenters pointed to the ducts themselves, suggesting that an animal might have died inside one. 

"Even a dead mouse will stink out the whole house," one commenter wrote.

Others agreed, recommending that the OP inspect all accessible vents. Some users proposed DIY methods for checking in areas beyond an easy line of sight, such as by using a phone camera or an inexpensive endoscope.

Some commenters suggested that water or debris in a high-efficiency furnace's condensate pan or drain could be the source of the smell. Another cited the air conditioning drain trap as a potential area of concern, explaining that, if it had dried out, sewer gases could reach the ductwork.

Other recommendations

Still other commenters advised just shelling out the money to have a professional come and take a look. A call to an HVAC company could clarify the diagnostic cost before the homeowners committed to an appointment, commenters suggested.

"You should have a HVAC company come out," recommended one user. "Shop around. I just had one come out and it only cost me $100."

When an inspection leads to a replacement, Palmetto's Comfort Plan offers $0-down options and can save homeowners up to 50% on heating and cooling costs. Its plans also include 12 years of free maintenance. 

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Where can I learn more?

Strange smells and unexpected HVAC costs have sent other homeowners looking for answers, too.

• A first-time homebuyer encountered a musty smell after switching on the AC.

• A homeowner traced a musty smell to the crawlspace, prompting calls for a structural engineer.

• A widowed homeowner received a $10,000 HVAC cleaning quote, drawing skepticism from commenters.

• A homeowner discovered a damp filter and mold on the furnace a year after AC installation.

• A homeowner found brown-yellow goop at vents, and a carpet cleaner identified a worsening factor.

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