We recently moved into a property with 2 water heaters installed in the basement. During the inspection, we were told that the water heaters were relatively new, but the exhausts were "odd". Yesterday, we had a strong gas smell in the basement and promptly called the gas company. The representative told us that the cause was a downward draft of the flue gas.

A plumber came by and told us that he hadn't seen such an exhaust, and at first recommended we change the entire water heater, and after a while (seeing the neighbor's setup) told us to change the exhausts.

I have attached 2 pictures of the exhaust installation.

My questions are: Based on the pictures, is this a normal setup?

There is silver HVAC foil taped around the vent. I removed it off one exhaust and experienced a draft of air coming down in the basement, near the water heater. Would it help to reseal the duct with foil tape, poking holes in it, so the exhaust can escape? This would be a temporary measure till I get some more opinions/estimates.

Both Exhausts Closeup showing the silver foil around the duct

  • Where are you located? these are natural gas fueled appliances? What is the make and model of the heaters? Do those windows open?
    – Tester101
    Commented Feb 3, 2015 at 17:50
  • 1
    The Windows are the first issues I see, you are not supposed to exhaust under a window like that. Where is the Incoming Air coming from? Is one the Intake and one the Exhaust? If so, that is the other issue. Your intake may be too close to the Exhaust.
    – scooter133
    Commented Feb 3, 2015 at 19:29
  • 1
    Those vents are likely too close to the window. The smallest distance I could find was 12" below a window, but this should be specified in the manufacturers installation instructions.
    – Tester101
    Commented Feb 3, 2015 at 19:31
  • Are those "caps" open at the bottom?
    – Tester101
    Commented Feb 3, 2015 at 19:32
  • 2
    They make concentric Ducts that can be used for both. If they are High Efficiency units you can even use PVC. Looks something like this: hotwater.com/lit/misc/197313-001.pdf The Exhaust shoots out the top, then the intake is from under the collar. This Spec says you need 12" separation for 50,000BTU or higher. If you could do something like in Figure 5 you might be able to deal with the Window Opening too. It should be 12" from the opening.
    – scooter133
    Commented Feb 4, 2015 at 1:07

2 Answers 2


This is not a good example as the venting pipes are right below some windows which can leak exhaust gasses back inside the residence. This would be illegal in the state of Michigan.

  • Do you have a citation for that? (I agree it'd be silly if this wasn't forbidden by Code, but the citation would make your answer quite a bit stronger) Commented Jan 27, 2017 at 0:15

I suspect this is a very well sealed home and insufficient fresh air is entering to permit the unrestricted exit of flue gas ; so some flue gas is released in the house. If so, There must be some duct to permit outside air to enter the house. I added a duct ( about 8" X 16" ) that brought outside air to a gas furnace in a situation like that.

  • Not sure but it looks like there may be a duct below the radon unit. Commented Jan 31, 2018 at 16:31
  • @PlatinumGoose That looks like a dryer vent to me. Commented Mar 6, 2018 at 2:23

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