5 Things you Must know About Venting a Tankless Water Heater

In this article, we have briefly explained venting a Tankless Water Heater and 5 things you must know about venting with some expert tips and tricks

How to Vent a Tankless Water Heater

For the ideal performance of your tankless water heater, proper installation and maintenance are undeniable. But the process of INS & outs of venting may confuse you a bit. Though these units always come with manual guides for installation and instruction, sometimes it can be hard for you to follow each step perfectly.

You don’t need to worry about it anymore, because we’ve arranged a complete and detailed guide for venting a tankless water heater for you to follow.

Why There Is A Need To Vent A Tankless Water Heater?

All gas tankless water heaters require a venting system. Gas burns, the combustion process creates heat and some harmful gases exhaust through it. In a tankless water heater, vents blow hot gas outside by exhaust so it can dissipate.

In a non-condensing tankless water heater, a venting system should be of stainless steel or thick aluminum so the hot gas can be exhausted.

There’s no need for metal venting for a condensing tankless water heater. Before we get into it, you might check top models of gas water heaters.

Things You May Need


Before starting the process, here is a list of things you might need during the venting process:

  • Termination Kit
  • Vent Adapter
  • Pipe Support
  • Bracket
  • Pipes (PVC, or stainless steel)

Venting Kits

A right vent and termination kit is always needed for your tankless water heater. Most of the units already have a vent installed in them but sometimes you need to buy separately. You may need to change your vent if the length of it is not right according to your need.

Here are some termination kits of different lengths:

  • 18-inch Rinnai Above Roof
  • Rheem 3 or 5 Vertical vent kit
  • 4-inch Z flex horizontal stainless steel
  • 3-inch horizontal vent.

5 things to know for venting a tankless water heater.

#1. Types Of Vent That Can Be Used

It depends on your particular model that which type of vent does your tankless water heater requires, but mostly there are two ways to vent a water heater.

Direct Venting:

An illustration to understand the direct venting mechanism

In this type of venting, air from outside comes in through the vent and then exhausts the vents too. This system is beneficial because it requires a small area to place the unit. A concentric or dual venting can be done in them.

In a concentric vent kit, there are intake and exhaust both placed on the same pipe. To avoid heating the exterior of the vent, the exhaust is placed in the center. This can help you to put units wherever you want.

There will be two separate pipes in a dual vent system, for intake and exhaust. In this case, location matters a lot because exhaust can get hot. Pipes are mostly made of PVC because you can’t seal stainless steel with silicon.

Power Venting:

An illustration to understand the power venting mechanism

In power venting, the intake is placed on the body of a tankless water heater instead of a vent pipe. The inside air vent through it while exhaust leads out of the house, and needs a larger area to intake air properly. 

#2. A Guide To Vent A Tankless Water Heater

The process of venting tankless water heater by following the manufacturer’s guide makes it easy to install a water heater. The efficiency and effectiveness of operating water heater increase significantly. The probability of any kind of danger and risk will be avoided. There could be either vertical venting or horizontal venting.

Horizontal Installation:

Horizontal installation can be done in two ways. By installation in a downward slope where an adapted will be needed for vent with a hose curated with stainless steel of proper length. So the exhaust will be outside of the sidewall of your home.

The inside and outside walls of the vent will be connected with a plastic cap or small metal. The installation will be terminated with a 90-degree elbow.

While in the case of vertical installation for upward slope there will be a need for a condensation trap.

Vertical Gas Water Heater Installation

A lot more variables are required for vertical installation as compared to horizontal installation. The parts necessary for installation will remain the same in both cases.

You may need to buy an adapter, condensation trap, fire stop, storm collar, and a rain cap.

Combustion Air:

Combustion air is important in the tankless water heater. Things needed to know are the way to deliver combustion air and the abundance of combustion air. If it is installed in an open space there will merely be air entering inside your home.

A gas tankless water heater using combustion air must have a minimum area of 10,000 cubic ft. near the water heater. Closets need air ducts & extra air inlets. Units that require combustion air from outside are needed to have a second hose put into them.

#3. Options for Venting a Tankless Water Heater

Several options can be used for venting a tankless water heater. It is your choice which option suits you well.

Non-Direct Fan Assisted Vent Outdoor:

This option fits for both vertical and horizontal venting. Gases can be pushed outside with the help of an electric fan. The oxygen that is needed for combustion comes from inside.

Fan Assisted Sealed Combustion Direct Vent Indoor:

Both vertical and horizontal venting can be done in this. Combustion air comes from outside that delivers to the gas burner. There is a sealed cover that prevents the usage of air from the area where it is installed.

A concentric pipe and two fits pipes run through a water heater from the wall of the roof. One pipe is for the intake of fresh air and the other one is for exhaust.

Fan Assisted Sealed Combustion Direct Vent Outdoor:

In an outdoor system, combustion air enters from the atmosphere and moves out through exhaust by the constant way. In warm climates, this kind of venting is highly recommended because it is cheaper and efficient.

#4. Tips For Venting Tankless Water Heater

Here are some tips mentioned for you to keep in consideration while venting your tankless water heater.

It Is Not necessary To Vent The Water Heater Through The Roof:

The venting part of installation becomes more expensive if it has to go always through the roof. By venting through sidewalls, there is more flexibility to put the unit anywhere easily.

No Need To Vent The Outdoor Tankless Water Heater:

There are no extra venting requirements in warmer climates to install the tankless water heater. Tankless water heaters can withstand freezing temperatures without cracking. Heating elements working on electric supply help through it, but tank water heaters can freeze and they should be replaced by tankless water heaters.

Condensing Tankless Water Heater Doesn’t Require Mental Venting:

Almost 80% of the heat generated by a non-condensing tankless water heater can be transferred to the water. Leftover heat needs to be exhausted and requires metal venting. The condensing tankless water heaters are 90% efficient and lower the exhaust gas temperature so they can be vented easily with less expensive materials such as PVC.

No Need For Separate Vents For Multiple Heaters:

Multiple heaters may be required to place in commercial and large-scale residential places but there are certain venting systems available in the market that uses the same exhaust and intake vents for eight tankless units.

The Venting System Shouldn’t Be Ugly:

Some manufacturers have designed vents that are aesthetically pleasing in style. People prefer tankless water heaters but hate a pipe sticking out of the wall. There are attractive covers and termination points present in the market, so there is no problem at all left to buy a tankless water heater.

#5. Is There A Need To Vent An Electric Tankless Water Heater?

No, an electric tankless water heater does not require to be vented and it has a lot more options in comparison to the gas tankless water heaters.

The main problem with an electric tankless water heater is GPM, and they are better for point-of-use applications or can be used in homes where is less demand for water.

As venting isn’t necessary for electric tankless water heaters, their installation cost often gets cheaper and they operate more efficiently as compared to gas tankless water heaters.

About Zarmish Fakhar

Zarmish has been working as a freelance research writer for 5 years. She is a Zoologist and social media activist as well. She has worked for many reputable newspapers including Dawn. She is a valuable member of Aqua macho as her passion for clean water and eco-friendly products are booming day by day.

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