I am in the process of installing an outdoor natural gas tankless water heater. The issue I'm running into is clearances around the heater. There's a small spot on the back wall of the house where I'd like it installed.

The installation instructions require its exhaust vent to be located at least 12" away from an open window, but in order to meet this requirement I would need to mount it right next to my main electrical service panel (and electric meter).

The only code requirements I've found regarding clearances around an electrical panel are allowing at least a 30" working space (side to side). From what I understand, the panel can be located anywhere within that 30" boundary, so if this is the case I believe I can mount the heater pretty much right next to it as long as there's enough clearance on the opposite side to get me to that 30" width.

I've attached a graphic that shows the measurements on the house and a diagram that gives an example of how to comply with the electrical code:

Diagram Electrical code

  • 1
    Given your use of inches, you're in the United States, Myanmar or Liberia. Which is it? Apr 10, 2020 at 12:23
  • I'm in California!
    – Synthetix
    Apr 10, 2020 at 13:08
  • There may be another issue here, esp. in California. Where will the exhaust vent be? I think there are rules about venting it next to a window that opens. Apr 10, 2020 at 13:28
  • @GeorgeAnderson The heater will vent directly to the outside, as the exhaust outlet is on the front. There needs to be 12" of space between the vent and an open window.
    – Synthetix
    Apr 10, 2020 at 13:57
  • How deep is the heater (distance from wall to front of heater) compared to the existing panel? Apr 10, 2020 at 14:01

1 Answer 1


The 30” requirement can start at the left side and be measured to the right. As far as the vent you will want to extend it through the roof. The amount of heat coming off a tankless is much hotter than a standard tanked water heater.

  • Since this is an exterior mounted tankless heater, the vent is on the front of the unit, facing outwards away from the house.
    – Synthetix
    Apr 10, 2020 at 13:58

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