Key Venting Requirements for Tankless Water Heaters

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There are many benefits of installing a tankless water heater in your home. This type of water heater is known for its efficiency, endless water supply, and the ability to be installed closer to hot water outlets and in smaller, tighter spaces.

If you are considering installing a tankless water heater, you’ll need to consider the venting and how you might want it installed. A poorly ventilated unit can cause your water heater to fail and present significant dangers.

For this reason, it’s important to know the venting and exhaust requirements of a tankless water heater.

outside tankless water heater installation

What are the Tankless Water Heater Venting Requirements?

First, let’s talk about why natural gas tankless water heaters require ventilation.

Tankless water heaters that use combustion to heat water need fresh air for the combustion process (oxygen is required to make fire), so fresh air must be drawn into the unit. Combustion leaves leftover gases like carbon monoxide, which is dangerous to humans and pets. These leftover exhaust fumes must be vented outside the house for safety reasons. Condensation drain lines may be required in addition to ventilation piping.

On the other hand, electric tankless water heaters do not use combustion for heating and, therefore, do not require venting. If you’re unsure which tankless water heater is right for your home, consult with a professional plumber.

Tankless Water Heater Fresh Air & Exhaust Ventilation Requirements

While a tankless water heater can be installed in a small, tight space, that tight space will not provide sufficient fresh air to allow for proper combustion. Negative air pressure will occur, and the tankless water heater combustion will suffocate, straining your unit and reducing its service lifespan.

Consequently, a natural gas tankless water heater in a small space will require both a fresh air vent and an exhaust vent. This means two vents with three-inch diameters reaching outside from wherever the tankless unit is installed.

Some tankless water heater manufacturers offer concentric venting, a double vent combined into a five-inch diameter pipe. The exhaust vent is in the inner section so that the vent isn’t hot to touch, and the fresh air moves through the outer section of the vent.

Alternatively, a tankless unit may be placed in a larger open space with enough fresh air for combustion, such as in a basement. In this scenario, only an exhaust vent is required.

Proper ventilation, regular maintenance, and descaling are essential to maintain longevity and tankless water heater efficiency.

Do the Tankless Water Heater Vents Need to Go Through the Roof?

Venting through the roof is not necessary for tankless water heaters. Instead, vents can take a 90-degree angle and vent through a wall.

Combustion fans blow exhaust out through the vent and suck fresh air into the unit. If you have both a fresh air and exhaust vent, they must be a minimum of 12 inches vertically and horizontally distant from each other to prevent recycling vented exhaust fumes into the fresh air vent. Placing the vents even further apart is even better.

Horizontal venting should slope away from the tank so that condensation does not run into the unit and damage the heat exchanger. If you cannot do that, or if your venting is vertical, you must install a condensate drain within three inches of the vent connection.

Can Tankless Water Heaters Be Installed Outdoors?

Some tankless water heaters are rated to be installed outdoors. They have self-warming features that keep their components from freezing in the winter. Recessed boxes can keep the outdoor tankless water heater units looking nice and protected from the elements.

These units are only designed for southern states, however. Winters in the northern states get too cold to handle. If electricity were to be knocked out, the self-warming feature would not be able to handle the cold of certain locations.

Can Tankless Water Heater Vents Be Combined?

Vent lines for tankless water heaters can be combined with those for other tankless water heaters. They should not be combined with other venting, such as stovepipes, chimneys, or bathroom fan vents.

A large house or a point-of-use system may require multiple tankless water heaters. The ventilation system for these units can be combined.

What Are the Ventilation Material Requirements?

The level of tankless water heater ventilation requirement will depend on the temperature of the exhaust.

A condensing tankless water heater recycles the exhaust fumes and gathers additional heat from it before it gets vented. At a heating range of 1,650 degrees, a condensing unit is about 95 percent efficient. The exhaust fumes then are somewhere between 90 and 120 degrees Fahrenheit. This lower temperature means less expensive plastic, generally PVC or polypropylene, can be used to make the vents. Plastic is cheaper, and easier to work with and install.

Plastic vents cannot handle high temperatures, however. Condensing tankless water heaters are significantly more expensive than standard tankless water heaters, which operate closer to 80 percent efficiency. With 80 percent efficiency, the exhaust fumes are in the 300- to 400-degree range. For these higher temperatures, category-3 piping is required. This will be constructed of metal, either stainless steel or thick aluminum. The exhaust pipe should not directly touch flammable or temperature-sensitive materials, so installation can be challenging.

The cost of installing a category-3 ventilation system may be high enough that it may be worth upgrading to a condensing tankless water heater. Category-3 pipes are more expensive to purchase, are harder to work with, and are harder to install.

Professional Tankless Water Heater Installation Services

Apollo Home proudly offers expert tankless water heater installation services in Greater Cincinnati, Northern Kentucky, and Dayton, Ohio. If you need a tankless water heater installed, our certified plumbers are ready and willing to help.

We know the best practices and building codes with tankless heaters. We will ensure that the ventilation system is set up correctly to ensure your safety and the longevity of your tankless unit. Contact us today at 513-506-0791 to learn more!

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