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Question DetailsAsked on 10/19/2011

Carrier Infinity system has mildew odor starting on 4th day of running?

Installed a Carrier Infinity forced air furnace with a humidifier and air purification system in November 2008. Have had no problems until this fall. Everytime we turn the furnace on we get a very bad mildew smell coming through the vents starting on the fourth day. We turn the system off, the smell goes away. We turn the system back on, after having it off for several days, and the mildew smell comes back on day four. When we noticed this upon turning it on the first time this fall we did have the installer come out and clean the furnace and check it out. He changed the humidifier filter when he cleaned the furnace. Anyone else have this problem? Ideas on what is causing it. I should add that all vents were cleaned out just prior to the furnace being installed. We never had this smell when we had an old oil furnace.

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2 Answers


you have the top of the line unit but you have a drainage problem the condensate that is form from the evaporator is not totally drained leaving stagnet water in the pan couple of things could be wrong first: the unit is level opposite of what is called for tilting back away from the drain. second: the drain pipe could be in the wrong outlet. there is two drain outlet one for drainage and the other one is for overflow. If the pipe is srewed into the overflow side the drain pan will have a layer of condensate that will never be drained. remember mildew starts and mold is not too far behind. If that happens you have a major health hazard. If the pipe is in the right place then you have a flow problem that could be taken care of with a condensate pump. I hope this educates you as for what to look for so when you recall your tech he does not snowball you

Ray Gonzalez

koolray heating and air


Answered 9 years ago by Raymond Gonzalez


Since ducts were cleaned, unlikely there.

As other comment said, evaporator (coil) is likely culprit - either because condensate drain pan is not draining, or because unit (or furnace fan) is short-cycling so there is a lot of moisture buildup on the evaporator when it runs, but the fan shuts off before it removes the excess moisture. This is real common, especially when a new A/C is installed - if the run cycle of the fan is not compatible with the A/C operation, including a delayed shutoff for the fan to continue evaporating the moisture on the coil after the A/C shuts off, you can get rapid mold growth.

Humidifier is another very common place for this - the element itself if rotating element type, the pan it picks up the water from, or even lint caught up in the humidifier box itself.

Since it comes back on day 4, not right away, I would put my bets on the evaporator rather than the humidifier, because I would expect the humidifier to smell right off the bat if it were moldy. Ditto to the evaporator pan not draining out right - I would expect that to smell right at startup if it were holding water and molding. When was it last cleaned - you say new furnace installed in 2008, so 7 years ago - if your evaporator is not cleaned the lint buildup on it provides feed for mold to grow on when it gets wet running (which is unavoidable in residential-class normal systems), so maybe it needs cleaning.

You need a good inspection with a blacklight (which shows mold) by an HVAC technician.

Answered 5 years ago by LCD

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