Just bought a house that had a new furnace installed this summer. Vent number 1 in the image is for the furnace (2 is the water heater and 3 is sump). As you can see in the image, 2 and 3 both would require water (rain/snow/whatever) to travel up before getting into the pipe, but the vent for the furnace doesn't. I am worried that a winding raint or snowy day, and moisture could blow right into this vent. From there is a straight and down path into the furnace.

Can I (or should I) install some type of flap or add another bend to the PVC to point it down?

I did notice that both neighbors seem to have the exact same setup as mine, and this is the first house I have owned so I just am not sure.

Vents for Furnace

  • 2
    Your sump pump blows water out right near the foundation? That seems counter productive.
    – Tester101
    Feb 27, 2012 at 20:01
  • I would expect another elbow to blow the exhaust down, though you may not be able to simply add another elbow. The exhaust can only be a certain length, and this length is shortened with each elbow. The max length should be stated in the manufacturers documentation, and/or local building codes.
    – Tester101
    Feb 27, 2012 at 20:04
  • 1
    @Tester101 yeah, that is something I am planning on addressing at some point too. A bit of grading on the back of the house is needed and at that point I was planning on looking in to that.
    – zk.
    Feb 27, 2012 at 20:13

3 Answers 3


No, any extra water (from snowflakes and rain) that run down the exhaust will drain out with the condensate.

However, if the furnace is off in the summer, might want to have a removeable end cap to keep the bugs, bees, wasps, etc. from nesting and also prevent children from sticking a hose down the pipe. A little water is OK, little Johnny playing fireman is not.

  • little Johnny playing fireman Too funny. Off topic comment yes, but hilarious.
    – Tim Meers
    Feb 27, 2012 at 21:45
  • 4
    little Johnny playing fireman is a clear and present danger. Little Johnny is the single largest driver of DIY repairs. Feb 28, 2012 at 15:21

I have the same setup, and this appears to be the industry standard for high efficiency gas furnaces.

What I have done is take a piece of plastic screen, and hose clamped it over the end due to a couple of 5 year old hooligans that run around my back yard and find such outlets very attractive for the experimental dropping of pebbles and other small items.

enter image description here

WARNING -- There is a danger here of the screen condensing and freezing, thus blocking the exhaust. You should remove it in winter time. If your local five-year-old hooligans cannot be kept away in the winter, then check it often for freezing in extreme cold conditions.

  • It is a pretty good height off the ground (I cannot see into it without steeping on something) so until the local kids get a bit taller I should be OK on this. But +1 for future kid fix :)
    – zk.
    Mar 1, 2012 at 13:43
  • I also wonder if birds would nest in there. Mar 1, 2012 at 14:43

I cover both the furnace exhaust and air intake with aluminum foil in the summer. Otherwise, wasps might nest in there. I turn off the electricity to the furnace and post a big note over the switch to remind me to remove the foil before turning on the furnace.

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