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I am planning out a kitchen remodel, and would like to move the main exhaust vent for the water heater about 4-6 inches from where it currently passes through the kitchen area. The catch is that I cannot change its path through the upstairs without significantly increasing the scope of the project. So I am trying to figure out if stepping it over through the kitchen, and then back to the original path would work.

The exhaust is 6in B-Vent. Water heater is in the basement, has a short lateral run to the exhaust stack (which it no longer shares with the furnace), and then goes up through the first and second levels to vent through the roof. I am thinking that rotating the lateral run about 20 degrees, and then a pair of 45s where we go into the second level should give me enough offset to do what I want in the kitchen.

Any reason this wouldn’t work/be safe? Or cautionary points to make sure I account for before setting off on this path?

Here is a quick sketch of what I have in mind: (exaggerating the movement for demonstration purposes, not to scale)

Venting sketch

Edit: I looked up the manual on my water heater as suggested, and it referred me to "the latest version of the International Fuel Gas Code". Looking at the 2012 version of said code, I believe this is the relevant section:

503.6.9.1 Category I appliances. The sizing of natural draft venting systems serving one or more listed appliances equipped with a draft hood or appliances listed for use with Type B gas vent, installed in a single story of a building, shall be in accordance with one of the following methods:

  1. The provisions of Section 504.
  2. For sizing an individual gas vent for a single, draft-hood-equipped appliance, the effective area of the vent connector and the gas vent shall be not less than the area of the appliance draft hood outlet, nor greater than seven times the draft hood outlet area.
  3. For sizing a gas vent connected to two appliances with draft hoods, the effective area of the vent shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smaller draft hood outlet area.
  4. Approved engineering practices.

503.6.9.2 Vent offsets. Type B and L vents sized in accordance with Item 2 or 3 of Section 503.6.9.1 shall extend in a generally vertical direction with offsets not exceeding 45 degrees (0.79 rad), except that a vent system having not more than one 60-degree (1.04 rad) offset shall be permitted. Any angle greater than 45 degrees (0.79 rad) from the vertical is considered horizontal. The total horizontal distance of a vent plus the horizontal vent connector serving draft hood-equipped appliances shall be not greater than 75 percent of the vertical height of the vent.

I would interpret this to mean that the change I am wanting to make (using 2 45 degree elbows to create an offset) is permitted, as long as my pipe dimensions fall into the correct range(which they do). Can anyone confirm?

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1 Answer 1

Do a quick search online for the brand and model of the water heater. Most manuals for install are available online, but of course this will depend on the age of the unit. The manual (in most cases) describes the limitations of exhaust pipe distances and in particular the inclusion of elbows in the flue. It is important to check as elbows reduce the ease of flow and will effectively reduce the capacity of the exhaust and distance the flue can run.

So worst case it can make the installation unsafe and it is right to confirm with a professional or the manufacturer.

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