I'm looking to add a new tankless water heater, which allows for pvc exhaust.

In California, USA, I think clearance requirements for a door is four feet horizontally or one foot vertically. Does this also apply to garage doors?

What clearance is required by code from this exhaust to garage door?

I see the required clearances from the manufacturer but many of them say refer to local building codes.

  • Here is a short read on code requirements for tankless water heaters. buildingincalifornia.com/wp-content/uploads/2014/01/… Aug 15, 2018 at 5:31
  • This might be helpful. Vent termination shall be per manufacturer’s installation instructions. Distances to building openings, floors, overhangs etc. must be maintained. Wall vents shall not discharge trough walls located 5 feet or less from any property line. Aug 15, 2018 at 5:33
  • When I installed my tankless (a Rheem) it came with clearances in the installation and operation manual. Yours should have something similar.
    – Hari
    Aug 15, 2018 at 16:27

1 Answer 1


PVC isn't actually a proper material for exhaust, despite what the manufacturer says -- use stainless instead

The exhaust gas temperature of a high-efficiency condensing tankless heater operating at 140°F water thermostat will hover around 170°F out of the box, and this simply gets worse with time and scale buildup, reaching 300°F or more as scale is a much poorer heat conductor than copper is. This causes a PVC vent flue to "cook" (it will turn tan, then yellow, then purple/brown) and sag (PVC pipe is rated to 140°F), leading to leakage and eventual total failure (in a decade or less) with its attendant CO(!!!!!!!!), hypoxia, and moisture-buildup hazards. In fact, failed PVC venting (due to heat) on a condensing boiler system is suspected in the CO death of a family of four on a high-end rental property in Aspen.

Instead, a stainless steel concentric or double wall vent system listed to UL 1738 should be used; stainless steel vent systems, applied according to their listing instructions, will neither corrode nor fail due to heat. If that is absolutely not an option, then high-temperature polypropylene venting (rated to 230°F) can be used as a fallback, but this requires an external, engineered interlock to shut down and lock out the burner fuel supply if flue gas temperatures become excessive for the material used, as tankless heaters aren't smart enough to do that on their own (yet) and will continue to turn up the fire as they scale up in an effort to keep up with demand.

Whatever material you use, keep it clear of the garage door

The 4' horizontal or 1' vertical clearance you mention, though, should be applied to a garage door, as per IRC M1804.2.6 point 2, which applies to any "door, window, or gravity air inlet" -- in other words, any opening where natural circulation of significant quantities of air is expected when the opening is open.

  • I can use stainless, I suppose. But I question whether my unit, behind scale filters, rated for cascading PVC venting, in the ventilated garage really poses the threat you caution against. Good answer, nonetheless! Thanks.
    – Matthew
    Aug 16, 2018 at 1:44
  • @Matthew -- the manufacturer ratings for use with PVC venting are based on overly optimistic views of PVC's performance and of the flue gas temperatures involved. Aug 16, 2018 at 3:12
  • The one edge that mounting in a garage gives, by the way, is that you can simply plop it on an exterior wall, which means that the vent system becomes trivial -- adapter, maybe an elbow, thimble, cap, done. Aug 16, 2018 at 3:13

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