Hvac experts

[Oregonhunter5]

we have an older home, 1960. With basement. In the WINTER, when the furnace isn't running, the cold air return smells like a sewage smell coming from it. Only in the winter. I pulled the vent, and the cold air vent area doesn't have duct work in the wall. So........has anyone worked on something like this?

Thanks!

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[filsonhand]

Is the furnace in the basement ??

 

[Oregonhunter5]

Yes

 

[filsonhand]

Does the basement have the same swamp smell ?? Maybe a sewer vent un capped and carrying over into duct and vents ??

 

[Joe13]

A sewage smell would indicate sewage - my house was built in 1959 and the cold air return uses the floor as one side of the four sided duct.

Any possibility you have a leaking toilet ring or pipe leaking sewer water into the floor? Smell may not be so pronounced after its gone thru the furnace and distributed around the house.


Dunno how sensitive your nose is but a decaying rat in the wall will smell aweful bad.

 

[Oregonhunter5]

I've got a good nose. But all can smell it. Again it's only in the winter. There's a slight smell in basement next to garage wall. Septic is in garage. Odd I know

 

[Stomper]

I've been doing HVAC/R for over 25 years now. What you described concerning the "cold air vent" is the "return air" that acts as the intake for the furnace blower.

It was common practice to utilize the cavities between the floor joists by "panning" accross the bottom of the joists to in effect make a "return duct" instead of installing a dedicated duct trunk line.

This was very handy in basements as it saved money in materials, as well as preserved overhead space and reduced sofits in finished basements. This practice is no longer allowed (for a long time now) under the current/modern UMC (Uniform Mechanical Code) for several reasons, like energy effiecincy, air leakage, fire resistance, etc.

IMHO when done PROPERLY, "panning" is an excellent way to make use of that space, but one of the most overlooked problems is if there are any plumbing/sewer lines that traverse or reside in the utilized joist cavities. It is VERY POOR practice to "envelope" a sewer drain line within those cavities, but in "olden times" no thought was really given to drain pipes leaking gases into the ductwork air stream.

It sounds to me like you have that very situation going on, and you should look into that sooner rather than later as those gasses can make you sick, dead, or even build up to "flamable quantities" if all the stars align just right.

Now you know one of the reasons why I only do industrial/commercial HVAC/R these days.

 

[Oregonhunter5]

Sheeeet
So is that leak somewhere between the return and the furnace? How can they find it? Can fix without drywall being pulled? Expensive??

 

[Stomper]

No way to tell you w/o seeing what you have, sorry.

 

[Oregonhunter5]

Well I think I have the fix then. Close off that return and find the least expensive resolve to get a return to the furnace that's closest to the furnace. Minimal damage.

 

[jbett98]

Have you tried pulling the return duct floor grills and shinning a bright light down inside to see if anything looks out of place?

 

[Oregonhunter5]

The bummer is, it's on the wall and you can't see very far cause of the angle.

 

[filsonhand]

If you have any turdhurder(brownarm) buddies you could run a seesnake camera thru the duct

 

[Stomper]

Be careful blocking off the return air to the furnace. It's imperative that enough air flows accross the heat exchanger inside the furnace or you risk permanently damaging it, or even causing a fire if the hi-limit switch is old and possibly inoperable.

If you make a temporary return air keep in mind the inlet should be at least 10' away from the furnace so you avoid sucking combustion fumes (aka carbon monoxide) out of it and circulating it throughout the house. This is especially relevant to a natural draft venting furnace.

 

[jbett98]

Let's back up a bit.
What type of furnace is it, gas, oil, electric heat pump?
Where in the house is the furnace located in reference to a bathroom, laundry or kitchen?
Floor joists generally run front to back if the house is built in a rectangle and there are beams and posts supporting them mid way. Since it's more the likely that you do have panned floor joists in the basement, are they covered with sheet rock or some other covering?

 

[Oregonhunter5]

Gas. Furnace is downstairs. Across the hall from the bathroom down there. Yes sheet rock covers all framing.

 

[jb11]

I have used inspection cameras to peak around corners where difficult to see , on some calls myself , just a thought. Post some pics if you get a chance. Like Stomper said theres a reason why I only do commercial work these days lol.

 

[308]

If you have any turdhurder(brownarm) buddies you could run a seesnake camera thru the duct

Isn't that what you do for a living...lol

 

[filsonhand]

Isn't that what you do for a living...lol

Only on the weekends, after you showed me how to wear green glasses its a lot more bearable..

 

[Stomper]

By "panning" are you referring to a plenum?

Panning is basically taking flat sheetmetal and affixing it to the bottom of joists across the open bottom of the spaces between joists forming a duct comprised of three sides being the building structure and one side the sheetmetal (aka panning) forming a cavity that can be used as a duct.

Here's a quick scribble of an end-view of what I'm talking about.