The house is old but the HVAC system is very new. The compressor outside said 2009, so it is a good bet the indoor units are similarly new. They were.
Entering the furnace room, not only was the furnace and AC equipment new, but so was the water heater.
Both exhaust flues were newer also. And they both entered into an older double flue, which had been there for some time.
The double flue was very long, approximately 15', and while I am not a fan of exhaust flues hitting another at a 90 degree angle, it is permitted here.
However, I heard, we all heard, a low-pitched whistle!
I listened to the unit, took off the cover, and put my ear everywhere. I could not locate the whistle. My clients both tried and they could not either.
Standing there it seemed to come from the back of the unit. But the position of two large, square return vents made it hard to get to the back side, about 8' from where we stood.
But I leaned over anyway, as best I could. What I didn't want to do was fall and crush the return ducts!
While I couldn't see anything, the whistle got louder, so I knew I was in the right spot.
Something didn't look right, but from my angle I couldn't really see it.
So I stretched out and put my camera into position to snap a shot of the union of the two exhaust vents and behold!
LOOKING AT THE PHOTO, WE SAW THE SOURCE OF THE WHISTLE!
The newer flues met the old at a slight angle, and the assembly is too short.
You can clearly see a gap at the top. But there is a large gap at the bottom!
It was very poorly put together!
The whistle is caused by the drafting air. A draft up a flue is a good thing.
HOWEVER, THERE IS ANOTHER PROCESS CALLED BACK DRAFT!
While the furnace or water heater is operating, the heated exhaust moves toward cold and passes up the horizontal and then vertical flue toward the roof and outdoors and higher atmospheric pressure. That movement is what caused the "whistle" we were hearing.
But, as the flow slows and that heated exhaust cools, the cold air from outside becomes heavier and heavier, and it in turn begins moving downward toward the furnace. As it does so it also pushes any residual gases inside the flue toward the interior.
THOSE RESIDUAL GASES CONTAIN CARBON MONOXIDE. IF THERE ARE GAPS OR HOLES IN THE EXHAUST FLUE ASSEMBLY, CARBON MONOXIDE BACK DRAFTS INTO THE HOUSE. CARBON MONOXIDE ACCUMULATES INDOORS.
The house is empty and had been for some time, but I would love to learn about who used to live there. Were they sickly? Low levels, or persistent levels, of carbon monoxide will make you feel like you have the flu. Did the kids miss a lot of school? Did they have pets, or did the pets die quickly? Carbon monoxide (CO)exchanges with carbon dioxide in the lungs instead of oxygen (O2). It attaches to the red blood cells, PREVENTING THE RED BLOOD CELLS FROM ATTACHING TO AND CARRYING OXYGEN TO THE BODY. The body absorbs the CO instead of O2 and eventually overloads the body, starving it for oxygen and causing death. The smaller the animal the fewer the red blood cells and it becomes easier to thus suffocate. Did they have plants and did the plants always die? Plants are particularly affected by carbon monoxide.
My recommendation: always, always, always check the exhaust tubing over gas appliances. Check it carefully! If it doesn't sound right, it probably isn't. And there should be no holes caused by corrosion and no gaps. The draft can be checked with the smoke from a blown-out candle. It pays to check the flow of the draft now and then. And you can do it!
AND WITH GAS APPLIANCES INSTALL AND REGULARLY TEST FULLY-FUNCTIONING CARBON MONOXIDE DETECTORS!
DOING SO COULD SAVE A LIFE OR TWO! AND THE LIFE YOU SAVE MAY BE YOUR OWN!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560