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Brian, Architect
Category: HVAC
Satisfied Customers: 3123
Experience:  12 years designing, specifying, troubleshooting HVAC systems
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When my furnace kicks on it smells like poop. What can I do

Resolved Question:

When my furnace kicks on it smells like poop. What can I do to stop this, it could be more like rotten eggs, the smell, but it reminds me of poop.
Submitted: 7 years ago.
Category: HVAC
Expert:  Brian replied 7 years ago.

HiCustomer Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way, it would help us to know:

-Do you have a bathroom nearby?

Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.

Customer: replied 7 years ago.
There is a half bath upstairs, but it's not directly over the furnace room, I would say it is about 5-10 feet away.
Expert:  Brian replied 7 years ago.
Where do you actually witness the smell? Is it blowing out of the heat registers? Near the bathroom? Throughout the house?
Customer: replied 7 years ago.
yes, it's coming out of the registers and we can smell it all over the house,and it is really strong in the furnace room. It doesn't always smell, only sometimes, and it was doing it occasionaly when the air conditioning was running over the summer, I do know that the previous owner had pets and he kept them downstairs, if they had accidents in the furnace room on the concrete floor would that cause a problem?
Expert:  Brian replied 7 years ago.


Welcome to Just Answer.

Sorry to hear about your problem.


The only way any smells from the basment could enter the system, is if the ductwork is leaky, meaning that the connections are loose or even diconnected, in the basement. If the ductwork is relatively tight, without any large air gaps or disconnections, then I would be looking at the bathroom that is closest to the return air grille.


The return-air grille draws air from the surrounding space to circulate it thru the ductwork. When a bathroom is nearby it will draw air from there, as well.

If the sink/ tub/ shower is not used often, the water that fills the trap, to prevent sewer gases from coming up thru the drain, can slowly evaporate, allowing an air space for sewer gases to escape. These gases will be pulled towards the return-air grille, sucked thru the ductwork and will dump out at all of the registers. To solve this, run the sink, tub/ shower faucets for a minute, at least once a month, to keep the traps full.


Another possible culprit, is if the wax ring on the bottom of the toilet is not sealing well, the sewer gases can be pulled past the wax and towards the return grille. To solve this, involves removing toilet and replacing wax ring. This is a little more make sure all the traps are full of water first and test it.


If you need further help or clarification on this answer, please do not hesitate to reply to this post.


Thanks for asking your question at Just Answer.

Best of Luck, Brian


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