I installed a new water heater and want to vent it right. The old water heater used ABS pipe since it had a blower. Basically I have a 3" b gas vent pipe coming in and connecting to a flex gas pip attached to the vent hood. I used 3 sheet screws to attach the flex to the hood and 3 sheet screws to attach the flex to the B gas vent pip that runs right outside and has the vent cap on it. Does this sound correct? No I just use screws and no tape? Thanks. enter image description here

  • Here are some things I notice, but there are likely other issues: Screws must be short so that they only pierce the outer wall. The horizontal section must be sloped towards the appliance (1/4 inper foot). There needs to be a total rise of 5 ft (inside plus outside). There should be a 1in separation between the vent and wood.
    – Pigrew
    Aug 6, 2015 at 16:03
  • @Pigrew What is the source of these requirements?
    – Tester101
    Aug 6, 2015 at 16:37
  • @Pigrew The old setup passed last inspection in idaho for the 5' total rise issue. The screws are short and dont pierce the inner wall. the horizontal section is 2' so I can try and angle it 1/2" total. Does this sound correct?
    – Packy
    Aug 6, 2015 at 16:48
  • @Pigrew I think the horizontal section should slope out not in. IRC 2012 G2427.10.7 (503.10.7) Slope. A vent connector shall be installed without dips or sags and shall slope upward toward the vent or chimney at least 1/4 inch per foot (21 mm/m).. But I could be mistaken.
    – Tester101
    Aug 6, 2015 at 16:57
  • IRC 2012 G2427.6.4 (503.6.5) Minimum height. A Type B or L gas vent shall terminate at least 5 feet (1524 mm) in vertical height above the highest connected appliance draft hood or flue collar. A Type B-W gas vent shall terminate at least 12 feet (3658 mm) in vertical height above the bottom of the wall furnace. G2427.6.11 (503.6.13) Fastener penetrations. Screws, rivets and other fasteners shall not penetrate the inner wall of double-wall gas vents, except at the transition from an appliance draft hood outlet, a flue collar or a single-wall metal connector to a double-wall vent.
    – Tester101
    Aug 6, 2015 at 17:09

1 Answer 1


Based on the International Residential code (which may or may not apply where you live), this installation is not compliant. Things that I see that need to be corrected include (but may not be limited to):

  • The vent must be held at least one inch away from wood and other combustibles.
  • The total rise of the vent must be at least five feet, to insure proper drafting.
  • The vent must be sloped so that water/condensate will flow towards the appliance, by at least 1/4 inch per foot.
  • Screws must be short enough that they do not pierce the inner metal of the vent.
  • The length of the horizontal section (defined as sections at less than 45 degrees) must be less than 75% of the total rise.
  • The vent cap outside must be a "type B" cap.
  • Don't use tape because it would burn. Any small gaps should be OK since the exhaust will pull extra air into the vent, instead of letting the exhaust into the room.

Also, I see that one of the corrugated copper water tubes is a little flattened. You may want to replace it. Also, I see the plastic dielectric at the end of the tube on the right, but not on the left. If there is not any plastic dielectric, I'd suggest replacing it with a tube that has a dielectric. These connections do NOT need plumber's tape or dope. Also, these corrugated tubes should be replaced when the water heater is replaced.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.