Rinnai Tankless Water Heater Venting Guide

Many versions of gas-fired Rinnai tankless water heaters are available, and you should read the instructions to discover how to install the vent on your unit. We’ll go through how to install PVC or CPVC standard venting with a non-return flue check valve. Remember that PVC and CPVC venting must still meet the installation and operations handbook criteria.

How should the vent on your Rinnai water heater be installed?

Rinnai Tankless Water Heater
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When it comes to venting, there are various issues to consider:

  • Putting in the check valve

The first steps are installing the check valve and securing the valve adapter to the exhaust adapter ring. The check valve adapter must be fully inserted into the exhaust adapter ring.

One screw from a pair should be inserted through the Exhaust Adapter ring. The second one must be screwed into the other side of the ring at the same height as the first one and at a 180-degree angle. Remember that the Exhaust Adapter Ring still needs a hole in the back.

  • Exhaust Adapter Ring Connection

Once more, one screw must be inserted into the Exhaust Adapter Ring through the front hole in the heater sheet metal. The second screw needs to go through the sheet metal’s backside.

The check valve must be assembled by connecting the components. Ensure the Non-return Flue Check Valve is connected to the 3″ PVC or CPVC mount. Applying the oil around the pipe’s outside diameter is also crucial.

  • Pour 8.5 ounces of fresh water into the check valve after attaching it to the adapter. Remember that you must remove the input cap to reach the intake airport.
  • Install 3″ PVC/CPVC into the intake airport and check the valve by carefully and squarely cutting the pipe end.
  • Through the hole created by the intake airport, fasten the self-tapping screw.

The traditional PVC/CPVC vent system may be modified similarly.

How should the header be put together?

For various PVC and CPVC pipe diameters, there are several tips:


  • It connects two pieces, either inline or in the corner.
  • The maximum header length is two units of 40 feet, and the full vent length is two units of 20.5 inches from centre to centre.


  • Use it with two or three tankless water heaters.
  • Get the 4″x3″ reducers and then the 3″ PVC or CPVC.
  • 20.5″ centre to centre is the length of the header.


  • It connects 2 to 5 tankless water heaters.
  • Utilizing reducers, you may use 3″ PVC/CPVC at the unit and connect to a 6″ header.
  • 20.5″ centre to centre is the length of the header.

Rinnai Tankless Water Heater

Is it hard to connect the venting?

When you precisely follow the steps, nothing is difficult:

  • Secure the check valve to the device using the self-tapping screw.
  • Directly insert the 3″ PVC/CPVC pipe inside the check valve.
  • It’s best to use the provided lubricant on the PVC/CPVS connection rather than glue. Glue could damage the check valve and render it unusable.
  • Use 3″ PVC/CPVC reducers for 4″ and 6″ PVC/CPVC systems.
  • The horizontal slope will be toward the unit of 14″ per foot. The combustion air pipe must never be angled toward the tankless unit.
  • The vertical vent requires a minimum of every 6 feet, whereas the horizontal support vent requires at least 4 feet.

The prerequisites for horizontal venting are as follows:

  • You must leave the building after this.
  • 20.5″ centre to centre is the length of the header.
  • Horizontal vent support is required every 4 feet or more. While the vertical is quite close to 6 feet.
  • The maximum spacing between the exhaust and combustion air ends should be 12 inches.

Check the prerequisites for vertical venting as well:

  • It must conclude outside the structure.
  • In contrast to the horizontal support vent, which should run at least every 4 feet vertically.
  • 20.5″ centre to centre is the length of the header.

What are the termination clearances for exhaust vents?

The terminations must be placed for direct vent applications to collect combustion air and remove the exhaust.

Are there any high-altitude changes that are necessary?

You must ensure the tankless water heater is fitted correctly for the PVC/CPVC regular venting to operate at high altitudes. For liquid propane and natural gas, the high-altitude installations are anticipated to function well up to 10,200 feet.

The first switching group should have DIP switches numbers 2 and 3 configured according to altitude. The switches SW2 and SW3 are set to the default value of 0-2000 ft. The gas pressure setting for the large size no longer has to be changed once you adjust the DIP switch.

Dos and Don’ts for vent installation

Installing the vent on your water heater entails some steps:

  • The vent length must be within the prescribed limits, and the clearances must be met.
  • Ventilation outside the application is required for the intakes and exhaust terminations.
  • Vent length describes any additional venting, terminations, and fittings required for building access. The header is excluded from this.
  • Only the venting ranges required to join multiple units spaced 20.5′′ centre to centre are included in the header length.
  • The following details pertain to the maximum comparable vent length:
    • 90-degree elbows equal 10 feet.
    • 45° equals 5 ft.
    • Ten feet at the tee termination
    • Vent length is defined as spacing more than 20.5″ centre to centre.
    • Vent connections must be connected to create an airtight seal.
    • The requirement is to connect the combustion air intake to the appliance and fasten it with a self-tapping screw.
    • Ventilation must be direct and use the fewest possible pipe fittings.
    • You should modify the tankless unit’s temperature setting.
    • Aim to keep the horizontal vent from sagging or dipping.

Remember that there are several regulations on the installation of vents:

  • Never mount using another distribution system.
  • Avoid combining vent components from various manufacturers.
  • Never attach the venting system to an existing chimney or flue.
  • Installing a water heater, venting, or vent terminations in an area with corrosive substances is not recommended.
  • Never use thermal insulation to cover a non-metallic vent pipe or fittings.
  • Avoid using galvanized ABS or cellular core PVC for the exhaust vent.


Following the instructions in the handbook will make installing the vent for your Rinnai tankless water heater simple. But you should seek expert assistance if you feel overburdened by the task.

Rinnai Tankless Water Heater