Tankless Water Heater Venting

Going for gas or propane tankless water heaters can be a smart decision you have ever made. Why is it so??… 

The reason is that tankless water heaters fueled by either natural gas or propane liquid are tremendously energy efficient and offer you 50% reduction in energy consumption. Therefore you save both energy and money. Another benefit of the system is that greenhouse gas emissions can be reduced by 61%.  

Tankless Water Heater Venting typesnting Types

To achieve maximum efficiency and performance along with safety, proper and effective tankless water heater venting is crucial. Moreover, regular maintenance of tankless enhances its lifespan. There are two models of gas tankless available in the market based on installation:

  • Indoor installation
  • Outdoor installation

There is only one major difference between the two models- the way they are vented. External gas models feature a front vents system and reduces the additional vent piping requirement. Whereas internal units feature exhaust vents. 

Going further, the interior gas tankless heaters have either direct vents or power vents to obtain fresh air. Both direct power vent systems work differently. In the direct ventilation system, the units stream fresh air from the outside. Moreover, they are ideal for confined spaces.

On the other hand, the power vent heaters require a larger area with sufficient air flow inside the home to draw fresh air for combustion. 

How To  Vent A Tankless Water Heater?

When installing a gas or propane tankless heater, venting should be done as mentioned in the company’s manual. By doing so, you reduce the risk of probability of carbon monoxide and the possibility of any upcoming danger.  

The use of PVC or stainless steel pipes is essential in the ventilation system. And they are pretty expensive as compared to CPVC or PEX. Designed with special stainless steel for tankless water heaters, these pipes do not corrode when they vent corrosive gases. It is worthy to note that standard galvanized venting is designed to vent tank-based water heaters as well as furnaces. But if you vent your tankless water heater through it, it will quickly rust your tankless heater.  

Further, you have choices regarding installation of tankless heater. It can be either vertical or horizontal. 

Horizontal Installation

There are two ways that make horizontal installation pretty easy. In the first method, you choose a downward slope that requires a 90-degree elbow for the vent as well as a vent hose crafted from stainless steel that is proper in length. This makes sure that exhaust stays away even from the sidewall of your home. 

A tiny plastic or metal cap is used to interlink the inside vent to the outside wall to finish the exhaust. The proper venting kit for tankless is no doubt the cherry on the top.

For vertical installation, you need to include a vertical condensation trap in addition to the above mentioned parts. 

Vertical Gas Water Heater Installation

Thanks to the tankless water heater construction, that ensures vertical installation along with some variables which horizontal installation does not need. They are an adapter, a 90-degree elbow and a condensation trap. 

Many tankless brands including Rheem gas water heaters do not require a condensation trap whereas the Bosch models feature inbuilt condensation traps. But purchasing stainless steel pipes and a fire stop is inevitable. The ceiling where ventilation is taking place, you need to attach a fire stop. The process will end by attaching the roof flashing, storm collar andrain cap together. 

Combustion Vent

For a gas tankless model to work properly, ample combustion air is crucial to vent effectively.  Many tankless heaters are capable of working in a variety of air conditions. Moreover, they do not draw fresh air from the outside zone where they are located. 

On the top of all, the gas heaters require a minimum of 10,000 square feet of open space around them for vetting. Meanwhile, in closed locations like closets, air vents and additional air inlets might be required. Another separate hose is essential for the models that draw combustion air from outside. 

The Best Ways To Vent A Tankless Water Heater

To find out the best venting option for tankless heaters is not a piece of cake. You need to consider many factors including the space tankless model and your budget. 

Following are some options that might help you to understand this in a better way. 

Fan Assisted Non- Direct Vent Outdoor

This vent is great for both vertical and horizontal installation. And it pushes the gases outside your home by using a fan that runs on electricity. For combustion, it draws oxygen present within space. 

Fan Assisted Sealed Combustion Direct Vent Indoor

This is also a versatile vent and can be done horizontally and vertically in an efficient way. To fuel the gs burner, outside combustion air is supplied. Incorporated a sealed cover, the heater does not utilize the air present around the area where it is located.

Consisting of two pipes, a concentric pipe gap that runs between the water heater and the wall/roof of the home. One of the pipes is for exhaust and the second one draws fresh air. 


Outdoor venting is suggested for the areas where the climate is warmer as it works best there. The exterior installation tankless heater draws air from the nearby surroundings and emits exhaust in a continuous flow. 

Tankless Water Heater Venting Types

Tankless water heaters are getting popular because of their versatility and easy installation. Coupled with multiple vent types, every model has its own unique functionality with a different price tag, spatial needs and the advantages associated with it. 

Tankless Water Heater Venting Types: chimney vent vs power vent vs direct vent

Choosing the optimal vent placement greatly depends on the tankless heaters’ position, size, location and the need for air intake. 

Talking about the venting pipe, a concentric 5 inch vent design features both intake and exhaust pipes. Thanks to the warm insulated exhaust vent for keeping this process cool. Another plus is the additional protective layer that saves from hazardous gases.  

A number of manufacturers provide recess boxes for mounting non-condensing tankless water heaters inside the wall framing rather than mounting them to the wall. Moreover, the stylish covers enhance the design and look of the models. 

Sidewall venting is cost effective and  more convenient than roof venting that is common in traditional water heaters. An intelligent plumbing can be helpful in such a situation. 

There are chances of freezing the models in colder climates but thanks to the built-in freeze protection features in the exterior tankless models that make them resilient against freezing. By the way, outdoor installation does not need venting and makes it the best option in a suitable atmosphere. 

When it comes to non-condensing tankless heaters, they are small and 14 inch wide make them compatible with the majority of the recess boxes. While the condensing boxes whose width is 18 inch approximately offer numerous advantages. 

In terms of efficiency, condensing models excel and are 95% efficient as compared to non-condensing units. They only transform 80% heat and produce exhaust gas. Therefore, at temperatures 110 to 120 degrees a condensing heater stays cool. 

Let’s discuss the types of venting.

Power Vent Tankless Water Heater


In power vent units, the combustion process utilizes indoor air, and the air is exhausted outside for the regulation process. Power vent units are configured in such a way that they require only a single exhaust vent. Due to the restricted space in the immediate area, these units require greater space with sufficient air.

Direct Vent Tankless Water Heater

direct vent tankless water heater

Two vents are provided on direct vent units; one pulls air in from outside and the other exhausts it. Ventilated units are equipped with two vents and use outside air for operation.

In closets and similar small spaces, direct vent units generate less excess air, which lowers the environmental impact. Approximately 16 square feet of space can be saved, making them an ideal choice for rooms with limited space.

Concentric Vent Tankless Water Heater

Concentric vents contain both an intake and an exhaust vent in one; they are 2 vents in 1. In order to obtain the best features from power vent and direct vent models, manufacturers commonly offer concentric vents.

The advantage of concentrator vents is that they have one pipe that serves as an intake vent and an exhaust vent. A hole is cut in the wall or ceiling, and the heating mechanism regulates the temperature as warm exhaust air is retained inside. This keeps them cool at all times. 

Since tankless water heaters have less surface clearance than traditional tank water heaters, they require less space when installed. As opposed to direct vents, concentrated vents aren’t hot to the touch. In addition to such benefits, concentric vents are far safer, as the exhaust air is contained, preventing leaking harmful gases into the home.

However, even though concentric vents are safer and more convenient to use, the pipes are typically larger, with a diameter of about 5 inches, as opposed to a standard 3 inches. 

Various options and approaches are available for properly venting your tankless water heater. Each offers distinct benefits and is suited to varying budgets and situations.

In order to maintain safety, functionality, and comfort, an efficient ventilation system is required. When it comes to setting up a ventilation system, you must always refer to the manufacturer’s procedures and professional suggestions. 


Do tankless water heaters require venting?

Electric tankless heater does not need venting. Whereas gas and propane tankless water heaters require proper venting to work efficiently. Further, only the indoor installation require ventilation system.

Can I use existing vent for tankless water heater?

No, the tankless water heaters do not use the common venting includes piping vent and masonry chimney flue. Rather, it requires special stainless steel venting or PVC.

What type of vent does a tankless water heater use?

A tankless water heater vents in two ways: 1) Power vent 2) Direct Vent

Can you vent a tankless water heater with PVC?

Yes, you can use use PVC with a tankless water heater for venting. Before installing, you need to check the PVC requirements.

Daniel Adley is a seasoned and skilled plumber with over 20 years of experience. Specializing in repairing and optimizing water appliances for large buildings, offices, and homes, he has a keen eye for efficiently identifying plumbing and maintenance issues. With a passion for his craft, Daniel brings extensive knowledge and expertise to every project, ensuring reliable and effective solutions for his clients.

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