When I turn on my Air Conditioner my laundry room drain smells.

[BamBoozzled]

Hi everyone! First post here looking for some help!

A couple years ago we had a sewer backup that left us with 3 feet of water in our basement. After that we had to replace our air conditioner and we started to smell sewer (the same smell from the flood) around our house. We thought it was the air conditioner but it seems that when the ac fan turns on the smell comes from the laundry room drain and fills the house. I have poured buckets of water, baking soda, vinegar, soap, and even canola oil to prevent it from evaporating. Then I removed the floor drain and got a toilet brush to scrub as far down as I can. The smell goes away for like a couple hours but then comes back up. We rarely use the room but it slowly creeps back out. We just placed new tiles so I am trying to avoid having to tear anything up... even if its a small nuisance. So I have had 2 ideas.

1. I Temporarily I filled a bag with baking soda and placed it atop a towel with a little bucket to keep it still. This seems to solve the problem but my mother is paranoid about gas buildup even though people seal drains all the time. I dont think this is possible since people cap drains all the time but I just wanted to ask your thoughts on it.

2. I was thinking about buying a one way valve https://www.amazon.ca/Liquid-Breaker-GD102-Green-Drain/dp/B00W2FPBJG/ref=sr_1_2?crid=26S85PY9BXJPA&keywords=drain+trap+seal&qid=1590503581&sprefix=drain+trap+sea,aps,145&sr=8-2 I hear great things about this and am seeing great reviews.

Basically I am on board to do any of the above two option but leaning towards more of the second. To be honest... my mom has made me slightly paranoid but in my level head it doesnt make any sense. I just really want the sewer smell out. It is weird because it only happens in the summer months which is june, july, august when we turn on the air conditioner. We also have a backflow valve in the laundry room. Other then that I am stumped for solutions. If this issue persists I may have to call a plumber but I just thought I would ask on here.

 

[Sylvan]

"my mother is paranoid about gas buildup"

She is very smart lady to be concerned about "sewer gases"

In most homes, sewer gas may have a slightly unpleasant odor, but does not often pose a significant health hazard.[5] Residential sewer pipes primarily contain the gases found in air (nitrogen, oxygen, carbon dioxide, etc.).[6] Often, methane is the gas of next highest concentration, but typically remains at nontoxic levels, especially in properly vented systems. However, if sewer gas has a distinct “rotten egg” smell, especially in sewage mains, septic tanks, or other sewage treatment facilities, it may be due to hydrogen sulfide content, which can be detected by human olfactory senses in concentrations as low as parts per billion. Exposure to low levels of this chemical can irritate the eyes, cause a cough or sore throat, shortness of breath, and fluid accumulation in the lungs. Prolonged low-level exposure may cause fatigue, pneumonia, loss of appetite, headaches, irritability, poor memory, and dizziness. High concentrations of hydrogen sulfide (>150 ppm) can produce olfactory fatigue, whereby the scent becomes undetectable. At higher concentrations (>300 ppm), hydrogen sulfide can cause loss of consciousness and death. Very high concentrations (>1000 ppm) can result in immediate collapse, occurring after a single breath.

Explosion risk[edit]
Sewer gas can contain methane and hydrogen sulfide, both highly flammable and potentially explosive substances. As such, ignition of the gas is possible with flame or sparks.[7] The methane concentration in open sewers is lower (7 to 15 ppmv) than the closed drains (up to 300 ppmv) in samples collected 2 cm above the level of sewage.[8]

 

[Sponsor]

 

[Sylvan]

Call a plumber and have them WATER Jet the sewer and waste lines .

If the have a small holding tank of water they can add bleach to kill any bacteria

Water jetting will remove any type of grease or soap scum build up and restore full flow

Also make are all traps have their seal and all clean out plugs /caps must be gas tight

 

[Reach4]

A couple years ago we had a sewer backup that left us with 3 feet of water in our basement. After that we had to replace our air conditioner and we started to smell sewer (the same smell from the flood) around our house. We thought it was the air conditioner but it seems that when the ac fan turns on the smell comes from the laundry room drain and fills the house.

I have a troubleshooting idea. Measure the pressure between the drain pipe and the laundry room air. To do that, shove some clear flexible plastic tubing about 18 inches into the drain. That should get the tube end well past the trap. Blow thru the room end to clear any water in the tube. Thrust the end that you just blew through into a glass, or glass jar, of water. About 3 inches, or more, of tube should go vertically through the water in the glass. The water level inside the tube will probably be the same as the water level outside of the tube in the jar, if the AC is off. What you will have constructed is called an open manometer.

Turn on the AC. What happens to the water level in the tube vs outside of the tube? Record the vertical difference in heights. Use a ruler.

You can buy clear tubing at a hardware store, aquarium shop, and some other places. If you know somebody who uses oxygen, they throw away a bunch of suitable tubing each month.

 

[BamBoozzled]

Call a plumber and have them WATER Jet the sewer and waste lines .

If the have a small holding tank of water they can add bleach to kill any bacteria

Water jetting will remove any type of grease or soap scum build up and restore full flow

Also make are all traps have their seal and all clean out plugs /caps must be gas tight

Thanks for the response. I just purchased the plug I posted but I have a question. Why do so many people plug drains they dont use with similar problems, I know of multiple people who have done this and whats the drawback if the drain still allows water in. Is this ok for a temporary solution as I get the resources together for a plumber? The drain literally never gets used.

 

[wwhitney]

What kind of A/C is it? (Room A/C, ducted central, ductless mini-split, etc) Does it share any ducts with your heating system?

Where does the condensate from the A/C drain to?

Cheers, Wayne

 

[BamBoozzled]

What kind of A/C is it? (Room A/C, ducted central, ductless mini-split, etc) Does it share any ducts with your heating system?

Where does the condensate from the A/C drain to?

Cheers, Wayne

Ughh, I dont know D: and it sucks. Here are some pictures though.

https://i.imgur.com/N0eJCBT.png
https://i.imgur.com/pn0Nf4Z.png
https://i.imgur.com/7KGEtw4.png

I do know that when the heater is on during the winter months we have absolute 100% 0 smell.

 

[Reach4]

I do know that when the heater is on during the winter months we have absolute 100% 0 smell.

AC comes from the same system? Is the furnace in a room with a door? If so, try opening the door, and the door to the basement, and see if that helps.

Also, check that the area around the furnace filter is sealing so that the blower air comes from the cold air return. Maybe use a little smoke to see where the air gets sucked in. Blowing out a candle is one way to get smoke.

Also, if the furnace filter is too clogged or restrictive, that would make leaks more significant. Is the cold air return intake upstairs unblocked, as it should be?

What changes the blower speed between AC and heating? Is that automatic? You may need to turn the blower speed lower for AC than it has been. You normally want a higher blower speed for AC than for heating.

 

[BamBoozzled]

AC comes from the same system? Is the furnace in a room with a door? If so, try opening the door, and the door to the basement, and see if that helps.

Also, check that the area around the furnace filter is sealing so that the blower air comes from the cold air return. Maybe use a little smoke to see where the air gets sucked in. Blowing out a candle is one way to get smoke.

Also, if the furnace filter is too clogged or restrictive, that would make leaks more significant. Is the cold air return intake upstairs unblocked, as it should be?

What changes the blower speed between AC and heating? Is that automatic? You may need to turn the blower speed lower for AC than it has been. You normally want a higher blower speed for AC than for heating.

This is something I can help with. The furnace filter just got replaced and not clogged, I dont know what the speed is but all vents are unblocked and spewing heavy. The furnace room is close to the laundry room but all of them have no doors on them. After I put the flooring down the doors would be last. My dad is looking to contact the hvac guy to see if its an issue on that end but I really dont think it is.

Do you know if there is any downside to using a one way drain that blocks water and vapour from coming out but allowing water in? We also have a backflow valve installed in the laundry room, do you think that can contribute as well? I also have 3 other drains in the basement that all dont smell, it is just the laundry one.

 

[Reach4]

The furnace filter just got replaced and not clogged,

Try removing the filter, and blocking the slot as a test. You could take the old element, if you have it, cut a big hole in the media, and put that back in. It would be a test. If that prevents the smell, consider a MERV 4 filter instead of a MERV 14. Or seal the gap that lets room air from leaking into the furnace blower housing.

http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf

 

[wwhitney]

The pictures you posted show the air handler and the A/C coil, with the condensate draining to a floor drain. Have you tried pouring a bucket of water into the floor drain? [In case the floor drain is trapped and connected to the sewer, and the trap is dry, although I don't know why it would only smell when receiving condensate from the A/C in that case, or originate in the laundry room.]

That same air handler is your heat source, and the hot air and cold air come out of the same vents in the house? If so, I don't see how the issue could be due to air pressure differences, as the duct system should move air similarly in both heating and cooling modes.

[BTW, what is the Honeywall device mounted on the return box? It appears to have its own condensate drain line and a bypass duct going to the supply plenum.]

Cheers, Wayne

 

[Reach4]

BTW, what is the Honeywall device mounted on the return box?

Flow-through humidifier.

 

[BamBoozzled]

The pictures you posted show the air handler and the A/C coil, with the condensate draining to a floor drain. Have you tried pouring a bucket of water into the floor drain? [In case the floor drain is trapped and connected to the sewer, and the trap is dry, although I don't know why it would only smell when receiving condensate from the A/C in that case, or originate in the laundry room.]

That same air handler is your heat source, and the hot air and cold air come out of the same vents in the house? If so, I don't see how the issue could be due to air pressure differences, as the duct system should move air similarly in both heating and cooling modes.

[BTW, what is the Honeywall device mounted on the return box? It appears to have its own condensate drain line and a bypass duct going to the supply plenum.]

Cheers, Wayne

I also poured down buckets of water in the drain there as well but why does that one not smell but the other does.

 

[Reach4]

I also poured down buckets of water in the drain there as well but why does that one not smell but the other does.

Huh? The drain that smells is not near the furnace/AC?

 

[wwhitney]

I have poured buckets of water, baking soda, vinegar, soap, and even canola oil to prevent it from evaporating. Then I removed the floor drain and got a toilet brush to scrub as far down as I can. The smell goes away for like a couple hours but then comes back up.

So if you do the above while the AC is unit is shut off, then does the smell return? If so, I don't see how it can be related to the AC, it's just related to hot weather, when you happen to run the AC.

Is it possible the floor drain doesn't have a proper trap? Have you stuck a camera down it to look?

Cheers, Wayne

 

[BamBoozzled]

I havent stuck a camera but you are correct whenever it gets hot the fan turns on too cool down the house and blows the sewer smell

-This is for Wayne

 

[BamBoozzled]

Huh? The drain that smells is not near the furnace/AC?

No and thats why im stumped, I go down on my knees and smell the drain near the a/c and there is nothing. I smell the one in the laundry room and it stinks. I even put paper towel over the drain and can see it rising indicating air is coming out of it.

 

[Reach4]

I even put paper towel over the drain and can see it rising indicating air is coming out of it.

Use Saran Wrap for that. Paper towel passes air.

Also, some smoke near the drain can detect air flow. Blowing out a candle or match is one source of smoke. You could ignite a piece of cotton string to make smoke.

 

[BamBoozzled]

Use Saran Wrap for that. Paper towel passes air.

Also, some smoke near the drain can detect air flow. Blowing out a candle or match is one source of smoke. You could ignite a piece of cotton string to make smoke.

Based on my previous fixes I have stayed down there for hours and the fan in the laundry room blows strong outside the hole while the a/c drain doesn't. I ordered a one way drain valve and I think I am going to just cap the drain as I continue to look around, Is there a downside to this?

 

[Reach4]

I ordered a one way drain valve and I think I am going to just cap the drain as I continue to look around, Is there a downside to this?

https://www.homedepot.com/p/Oatey-2-in-Drain-Trap-Seal-437412/309670229?

Sounds like a good idea. Your trap is probably missing or deficient.

If you had a working regular trap, you could stick a cotton cord or rope in there to the bottom, and find about 1.5 inches of wet due to water standing in the trap.

Some traps have a cleanout plug on one side of the bowl. Could yours be missing the plug?
If so, the gas will continue to come out of that side hole.