Thanks for the replies guys...
Mark, do you mean replace the cooling coil? Sorry, not in the business and not exactly sure of all the terms.
Hitman, the condensate pan has a drain that comes out the unit and is attached to a pipe that goes down the inside of the house. I am thinking this is one of the sewer lines. Not exactly sure if this is what the line is called.
Charlezz, I'm not an HVAC tech, but I am a builder. HVAC guys have mostly been looking at this from their side although they have touched on a possible cause.
You say the condensate pipes go down the inside of the house, If they are cut into the DWV vent and not properly trapped or poorly installed the odor may be from the sewer system (not a good thing).
Also you say it happens after the shower fan has been run, leads me back to the bathroom. If the house becomes depressurized when the HVAC system is on and the fan vent, DWV stack or both are near a soffit, ridge, or gable vent, these exhausts may be entering the HVAC and being blown into the conditioned space. (not my first choice but possible).
More likely the first scenario because if you are running warm water in the DWV system vapors will rise and be brought up by the chimney effect of the DWV stack.
Hope this helps, what is it Sherlock Holmes says? If all obvious choices have been exhausted, the answer is the least obvious no matter how implausible.
I thought you already checked the drain ?
post # 19 says this is a lennox dual pac. with an rtu why would the
condensate be piped back into the house? if it is
dropped into a vent & the condensate trap is dry it
could very well suck in odor from the vent. try repiping to
the edge of roof
Originally Posted by marvin
Here is the likely culprit. Good catch. However, piping to side of house could be against code. When the shower is run, the shower trap fills up with waste water, and the odor goes out the vent stack along with the sewer gas. If the condensate is piped to this at the roof level and it's trap is empty, unless it's a positive pressure trap it's going to mix that smell in with the supply air. The way the condensate line is run sounds like your entire problem......
If everything was always done "by the book"....the book would never change.