Setting up the fresh air intake vent for the Takagi tankless water heater using 3" (75mm) solid core PVC pipe.

This water heater is designed to use PVC pipe and fittings for both the intake and exhaust vents. Since I had to purchase a 10 foot length of 3" pipe for the exhaust and didn't need it all, I'll use some of the rest for the intake. It has to be pressure rated Schedule 40 pipe (red lettering - ASTM D1785) and not the non-pressure DWV (black lettering - ASTM D2665) pipe.

A 90° (quarter turn) PVC elbow at the top of an 18.5" length of pipe that puts the intake just under the garage ceiling. The supplied "bird screen" fits perfectly inside the end of the 90° elbow. Later, this vertical pipe was extended up through the garage ceiling. It functioned well in both configurations.

Since the water heater is in a non-conditioned garage, it's not an issue having the combustion air come from the same area, as shown in pg. 15 of the heater Installation Manual, screen capture below:
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There's both adequate volume and makeup air from outside to support the combustion air requirements of the tank less heater. The intake is well above the 18" minimum height off the garage floor to avoid pulling in gasoline fumes.

If this were installed inside, say in a utility closet, then the intake air would need to come from a non-occupied air space, or in a concentric vent pipe from outside. I could have gone with the concentric vent, but it's a lot more expensive and difficult to install. With the intake in the garage, it's easily accessible for inspection and cleaning if needed. It was eventually run up into the attic area. That required cutting a hole in the ceiling drywall and boards. Inspecting and cleaning the intake does involve a long trip through the attic which is only accessible from the other side of the house.

I found the 3" (and larger) PVC pipe fittings are somewhat hard to find and you need to shop around to find them at a decent price. I ordered this 90° elbow on the Home Depot web site since it's not stocked in my local stores. Your mileage may vary, just reporting my experience.

In light of this, using ABS might have been a wiser choice of material as it seems to be more commonly available in the 3" size, although one needs to be sure and get a solid core ABS and not the cellular core DWV pipe. Takagi does list PVC, CPVC, ABS and polypropylene as well as stainless steel as acceptable materials for intake and exhaust. They supply the PVC couplings with the heater, so that is one reason PVC was chosen as that seems to be the preferred material.

More to come, condensate drain in the next segment...

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Intro:
Louisiana Fairytale by Austin Rogers
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