How To Vent A Tankless Water Heater? [Detailed Guide]

So you’ve decided to install a tankless water heater you will have many questions in mind. Most important is to know if it’s safe to use without venting. This water heater saves space, provides hot water on demand, and uses less energy than traditional models, but selecting the right venting method can be tricky if you’re unfamiliar with its venting requirements. Venting your tankless heater is essential for your appliance’s safe, efficient operation. 

You can vent a tankless water heater through the side wall or right on top of your roof (high-pressure version). The Multiple venting options allow for more flexibility when deciding where to place the tankless water heater.

When running a gas-powered appliance in your home, you need to be sure that it’s properly vented. If you’re not sure how to vent it yourself, call a professional before attempting to repair the appliance.

A tankless water heater
A tankless water heater

Do tankless water heaters require venting?

As a general rule, all water heaters that operate on gas need a proper venting system. If you’re venting a tankless water heater in your home, you need to make sure that you are doing it correctly. Without proper ventilation, your heater can run inefficiently and risk fire or carbon monoxide poisoning. Before installing a tankless heater, find out everything you need to know about venting these types of water heaters correctly and safely to prevent any potential hazards.

Required Tools and Materials

For venting a tankless heater you will need basic plumbing tools like wrenches, pliers, and screwdrivers. I recommend that you work with an electrician for any electrical work that needs doing so he can make sure it’s done properly. Gather these things at hand before starting your venting job:

  • Termination kit
  • Vent adapter
  • Stainless steel, ABS, or PVC pipes
  • Brackets and pipe support

Step by step guide for venting tankless water heater

If you have an old tank heater it’s best to replace it with a newer tankless model. However, if your old water heater does not pose any danger or leakages, you can still save money by venting it correctly. This guide walks you through installing vent pipes for your water heater to make sure that it will work safely and efficiently. If you are looking for tips on venting a water heater yourself, read on!

  1. Follow the installation manual for installing the tankless water heater properly.
  2. Consider which termination method you will use: vertical or sidewall, separate pipes, or concentric.
  3. Pinpoint the exact location for roof or wall penetration where the vent will terminate.
  4. Install terminator kit.
  5. Install vent pipes from the water heater to the termination point.
  6. Allow at least a ¼ inch downward sloping of the exhaust pipe to the water heater. Also, ensure that the combustion pipe doesn’t slope down to the heater. Always make sure to dispose of exhaust according to local regulations properly.
  7. Attach pipe support and brackets within every 4 feet so that expansion can be allowed in your plumbing line according to the requirements of your local building code.

What type of vent does a tankless water heater use?

When venting your tankless water heater, you’ll have several options. If your setup allows, you may be able to use some combination of plumbing vents and wall vents. For your tankless heater to work efficiently, you must know how it will be vented and then install that setup correctly.

There are two types of venting that you must consider when purchasing a tankless water heater: Direct venting and power venting. Let’s learn more about each type of venting and which you need for the efficient running of your water heater. 

Direct venting

In some cases, it’s possible to install a direct-vent tankless heater. A direct vent takes in air from outside the house and gets rid of the exhaust gases. You can install it in very tight spaces or even in rooms where there aren’t any vents. A tankless water heater with direct vents can have concentric or dual venting kits.

  • Concentric vents

The intake and exhaust are located on a single pipe in a concentric vent kit as the exhaust is located in the middle to prevent the exterior of the vent from heating up. It is a better option because you can place this unit anywhere without worrying about sealing. 

  • Dual vents

As the name suggests, a dual vent system has two vent pipes where one pipe is for the intake and the other for the exhaust. This exhaust pipe can become very hot, so you cannot be more flexible with the unit’s placement. Also, you can only use PVC pipes as you need to seal with silicon which cannot be used for sealing stainless steel pipes. 

Power venting

Tankless heaters with power vents use indoor air for burning gas instead of outdoor air. A unit with a power vent has one exhaust fan and one exhaust pipe. Power vented heaters require more air for gas combustion, so they cannot be placed in small rooms. It would be best to put them in large enough rooms or rooms with open doors and windows. You can also place them in rooms connected to other rooms with louvers or other fresh air supply provisions.

The third venting option

If you can put a tankless heater in an outdoor location, such as behind your garage or out by your pool, you’ll not need to go through the process of venting it. All you need is to buy an outdoor tankless heater. This outdoor unit is built for harsh temperatures, so it can be used efficiently in cold environments as they have self-warming capabilities. However, in case of power cuts, these units will not be able to perform to their fullest and can freeze in below zero temperatures. So, it’s better to install a traditional water heater for colder climates instead of installing an outdoor tankless unit.

Frequently Asked Questions

Can you vent the tankless water heater with PVC?

Noncondensing tankless water heaters generate a hot exhaust gas, so metal pipes are a better option as PVC pipes can be compromised because of the excessive heat. However, many tankless heaters come with an electric blower fan that reduces the heat of the exhaust gas that goes through the vent, so venting with PVC shouldn’t be an issue. On the contrary, condensing tankless water heaters do not transfer too much heat to the exhaust gas, so cheaper plastic pipes, i.e., PVC or polypropylene vents, can be used effectively. However, always check the manufacturer’s instructions and your local codes.

Can you vent a tankless water heater vertically?

You can vent a water heater vertically or through the roof if you wish so. Most tankless water heaters have options to blow exhaust air vertically or horizontally through a combustion fan. If you prefer a vertical vent, you can set the fan direction accordingly. But, if your heater is installed in a room with high ceilings, the exhaust has to travel a longer distance, reducing the heater’s performance. 

Can you vent a tankless water heater horizontally?

Unlike traditional water heaters with a tank, you can vent tankless heaters horizontally. Venting horizontally through the sidewall presents the shortest distance for the exhaust to exit, which improves the heater’s efficiency. Also, you can blow the exhaust horizontally or vertically as required, so it’s up to you to decide which venting direction works best for you. 

Can you use galvanized vent pipe for a tankless water heater?

Galvanized steel is not very durable, nor is it as corrosion-resistant as stainless steel. The corrosive exhaust gas will quickly eat away a galvanized vent pipe, so it shouldn’t be used for tankless water heater venting. A stainless steel vent pipe is a better option as it won’t rust away easily. If your local codes allow, PVC pipes can also be used for venting a tankless heater.

Can a tankless water heater and a furnace share the same vent?

While the two appliances can share the same vent, it is usually not recommended. In most cases, the tankless water heater exhaust must be vented outside and will be too large for the furnace vent, which in turn could cause a buildup of gas. Moreover, tankless heaters with efficiency rates higher than 95% produce highly damaging exhaust gases that can destroy ordinary galvanized pipes, so it’s better to vent them exclusively.

Can you vent a tankless water heater into the attic?

Tankless water heaters release harmful toxic exhaust gases, so it is not advisable to vent into the attic. The corrosive nature of this exhaust gas can damage the support beams and the insulation present in the attic. Also, it’s harmful to breathing, so you wouldn’t want to vent the tankless heater into the attic.

Do electric tankless water heaters need a vent?

If you use an tankless water heater that uses electricity to operate, it’s safe to say that you probably don’t need a vent. These are also extremely energy efficient, with at least 98% of the energy taken by the unit being used to heat the water without wastage. It can be the deciding factor for many consumers when shopping for a tankless water heater. However, a gas tankless heater is cheaper and may last longer than an electric tankless heater.

Can a tankless water heater be installed in a closet?

It’s not that uncommon for people to do exactly that. Most tankless heaters have been tested and pass safety standards for installation in indoor or outdoor locations. When you choose an indoor venting option, it’s important to make sure you set up your unit properly and keep flammable materials out of its way. You can place a tankless water heater in restricted places such as under the sink, pantry, or even under the stairs storage area, following all safety precautions.

Is it normal to smell gas from a tankless water heater?

If your water heater is giving off a gas smell, it could indicate that you have a gas leakage in your heater. It is a hazardous situation that needs immediate attention. If you believe that the smell is coming from your water heater, turn off all pilot lights and turn off your main shutoff valve and any secondary valves downstream from your tankless water heater. Then call the local utility company or fire department for help.

Top tips for venting a tankless water heater

An improperly vented water heater can be dangerous and inefficient, so if you’re going to vent it yourself, you’ll want to avoid these common mistakes. Keeping that in mind, here are some top tips on venting your tankless heater properly.

  • Ensure a straight horizontal venting without dips by installing pipe hangers.
  • Venting should be direct with as few pipe bends as possible.
  • Connections should be properly sealed to prevent any gas leaks.
  • It’s not recommended to connect the venting system to an existing chimney.
  • Vent termination should not be close to other vents and exhausts.
  • Pay attention to the manufacturer’s manual to keep your distance from other objects. 
  • Keep the vents’ length short and avoid using a large vent pipe.
  • Vents ending at the roof should have a protective rain cover.
  • Do annual checks for leaks and damages to the venting system.


It’s easy to see how important it is for you and your family, to have a properly vented tankless water heater. Now that you know how to vent your water heater follow these instructions when installing it. Not venting your tankless heater can create dangerous carbon monoxide leaks in your home. Also, keep in mind that I have provided this guide just for informational purposes. If you have any difficulty in the installation or you have not done any technical work like this before, hire a professional to do it for you instead of exposing you and your family to any potential hazard

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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