Tips To Vent a Tankless Water Heater

If you decide that a gas tankless water heater is the best solution for your application, one consideration is venting. Proper venting installation is critical for your tankless water heater’s effective performance and lifetime.

What are the most important features of venting?

Before installing the venting for your tankless water heater, you should familiarize yourself with the following components:

  • Stainless steel vent adapter and exhaust

The vent adapter is required for connecting the tankless unit to the exhaust line. Depending on the tankless water heater you’re installing, you can choose a 3in or 4in the converter.

Vent pipes must be constructed of stainless steel and UL-approved, and PVC piping is not an option.

  • Outdoor installation

If installing venting for your indoor unit seems too difficult, you can always opt for an outdoor unit. Look for equipment that is intended for outdoor use and does not require venting.

What are your choices for venting a tankless water heater?


Rheem 9.5 GPM Propane Indoor Tankless Water Heater


The manufacturer’s instructions must vent the tankless water heater. Proper venting guarantees that your tankless water heater operates efficiently while lowering the potential for hazards and carbon monoxide poisoning.

Tankless water heaters necessitate horizontal or vertical venting, often known as water heater venting via the roof by some.

  • Installation on the horizontal plane

There are two techniques to place the vents horizontally, the major one being:

You can utilize a downhill slope to attach the vent adapter, a ninety-degree elbow, and the stainless steel vent hose. The tube should be the correct length, and the exhaust should be kept outside the home’s walls. Connect the inside of the vent to the exterior using a little metal or plastic cover. The installation requires a 90-degree elbow.

You must incorporate a vertical condensation trap into the components in a vertical installation with an upward slope.

  • Vertical installation

Vertical installation is far more adaptable than horizontal installation since it considers various factors. However, the plant’s requirements may remain the same. You’ll need an adapter for the vent, at least a 90-degree elbow, and a condensation trap.

Some manufacturers allow you to skip the condensation trap, whilst others include them as standard. Add stainless steel to your shopping list since you need it for the discharge pipe that will exit your home. A fire stop is also required for each ceiling through which the water heater is vented. Remember to acquire a roof flashing, storm collar, rain cap, or 90-degree elbow to finish the attachment.

What about the air used in the combustion process?

Combustion air is required for tankless water heaters, and you must understand how to supply it to the device. When installed in an open area, combustion air will not carry any air inside the home.

Some tankless water heaters can operate in environments where they do not gather fresh air from outside the installation.

Any tankless water heater that uses combustion air must have at least 10,000 cu. Ft. of space around it. Air ducts and additional air inlets are required in enclosed locations such as closets. Models that need combustion air from the outside should include a second hose that must be installed. It will filter the air from outside your house into the surroundings where the device is installed.

What are the most popular options for venting a tankless water heater?

Venting the tankless water heater is difficult, and you should consider your alternatives before deciding on the ideal scenario for your application.

  • Outdoor fan-assisted non-direct vent

It’s an excellent option for both horizontal and vertical venting. It has an electric fan pushing the gas outside the chamber, removing the oxygen needed for burning.

  • Indoor fan-assisted sealed combustion direct vent

It supports both vertical and horizontal ventilation. The gas burner receives combustion air directly from the outside.

The water heater has a sealed lid and does not require air from the installation area. You install two pipes, one for exhaust and one for fresh air intake (one concentrical flowing from the water heater through the wall/roof).

  • Outdoor

The outdoor tankless water heater draws combustion air from the surrounding environment and consistently emits exhaust. It’s a safe bet for hot climates.

Some ideas for venting instead of coming to a decision

Top Choice

Rinnai RUC98iN (9.8 GPM)

Rinnai RUC98iN

Rheem RTGH-95DVLN (9.5 GPM)

Rheem RTG-95XLN-1



Venting a tankless water heater isn’t easy, so here are a few pointers:

  • Outdoor tankless water heaters free up space within the home and eliminate the need for additional emissions.
  • Indoor tankless water heaters draw in outside air. They are either the direct vent or the power vent ventilated. Direct-vent systems draw air from home, whereas power-vent units only use an exhaust vent. They require a bigger installation area to receive enough air for burning.
  • Condensation tankless water heaters are less expensive to install. The exhaust vent is built of plastic or PVC, which can only reduce costs.
  • As appealing emission solutions, pipe coverings and innovative termination locations stand out.
  • Recess boxes allow tankless water heaters to adjust behind walls rather than hanging from the home’s façade. The arrangement allows the water heaters to fit inside the house’s frame without turning from the ceiling.
  • Tankless water heaters with coaxial venting offer various safety advantages. If any pipes begin to leak, the air will remain within the coaxial vent and not enter the house. Learn more about it here.
  • Tankless water heater venting designs allow you to experiment with numerous emission possibilities. They can employ fans to blast exhaust from the unit horizontally, allowing vents to terminate in different locations throughout your home.