Sewer smell

[Joely]

hello! Any ideas welcome! We moved into our home earlier this year in May. (1200 sq feet near the beach in MS) The home had been seasonly rented but then completely vacant for around 4 months before we moved in. We did not have any issues the first few weeks. Later in the summer (getting worse as it gets hotter) we get an awful smell in the house. It is hard to describe but it’s just an overwhelming nasty smell. We have smelled every inch of the house and it does not seem worse in one place over another. If anything, the larger living areas smell worse than bedroom areas (which are all to one side of house/shaded by trees. Laundry area smells good compared to the rest of home). The smell also ONLY occurs between 12:00-3:00PM. The smell will come in (we notice the vents), circulate through vents, we deodorize and it is gone until next time. However it is enough to make the house smell foul. Sometimes it may go a week without doing this and sometimes it’s a few afternoons in a row. We regularly put water down drains and flush things not in use. We had an HVAC tech come in and clean our entire unit and find no issues. The house was built in 1914 but has been completely renovated within the last 5 years. We love this house but the smell is beyond frustrating!

 

[frodo]

is your AC unit in the attic?
if so, check and see where the pan drain from the unit/ condensate drain
terminates at.

some idiot may have drilled a vent and inserted the 3/4'' condensate pipe into it

also...check the vents outside on the roof..are they above the roof line?
if below, the wind could be forcing the smell down instead of up and away.

also..check the washing machine stand pipe

 

[Joely]

Thank you for your response! Yes, the AC unit is in the attic. There is a drip pan under the unit, but the main condensate line I believe is a 3/4” and leaves the unit and ties in to a 4 or 6” vertical pipe which penetrates the roof to a vent runs down through the walls.

 

[frodo]

that is your problem.

the sewer gas is migrating up the sewer vent pipe, and into the 3/4 line
then it is being sucked into the ac unit via the condensate pipe

once it is inside the ac unit the fan spreads the funk all around the house via the duct system.

here is the ''fix'
i have separate fixes
1] cut the vent pipe and install a 1 1/2'' ptrap and a tee into the vent pipe
turn the condensate line into the p trap with a elbow
2] re route the condensate line to a eve vent. and turn out of the eve screen with a elbow
3] re route the condensate line to above the bathtub. stick a pipe out the ceiling and let it drip into the tub
4] re route condensate line to the washing machine stand pipe. this can be done exposed behind the washer
5]
where is the pan drain run to? tie that sucker into the pan drain line

 

[CT18]

If you put a trap in your attic make sure that condensate dumps into it year round or the trap could dry out

 

[Diehard]

A very common arrangement is to have the trap on the condensate line, in the attic, and have the line drop on the exterior of the house onto the ground. I typically collect it and use it for my plants.

Concerns for the trap drying out, I believe would apply primarily when the line is routed to a potential source of sewer gas.
The primary purpose of a condensate trap is to prevent air from moving in or out of the coil box or air handler during operation.

EDIT: After being reminded of the negative air pressure pulled by the air handling unit, that would be the PRIMARY purpose of the trap.

 

[frodo]

A very common arrangement is to have the trap on the condensate line, in the attic, and have the line drop on the exterior of the house onto the ground. I typically collect it and use it for my plants.

Concerns for the trap drying out, I believe would apply primarily when the line is routed to a potential source of sewer gas.
The primary purpose of a condensate trap is to prevent air from moving in or out of the coil box or air handler during operation.

if it is installed correctly then you are correct, if it is not installed correctly then the trap does not work

the pre-fab 3/4 bent p trap s that you can buy do not work
the trap seal is to shalllow

 

[Diehard]

Agree frodo!

But why not explain why the trap does not work if not installed correctly.

I know of one instance where it wasn't installed correctly and resulted in a water stained ceiling.

 

[frodo]

Agree frodo!

But why not explain why the trap does not work if not installed correctly.

I know of one instance where it wasn't installed correctly and resulted in a water stained ceiling.

The trap depth is sized to overcome positive or negative static pressure of the blower fan

to small a trap. and the water is sucked out, to large a trap, and the unit will not drain

 

[Joely]

The trap depth is sized to overcome positive or negative static pressure of the blower fan

to small a trap. and the water is sucked out, to large a trap, and the unit will not drain

Thank you very much for your help. The drain pan has a 3/4” line that runs directly out the side of the house and penetrates the wall just below the roof line and just drips onto the ground.

Do you believe the easier/more efficient fix would be just tying into the pan drain line, or installing the p trap on the current drain line? If I were to go the route of tying into the pan drain line, how should I seal the opening on the current vertical sewer vent pipe? Thanks again! Attached are a few pictures for reference.