How to Vent a Tankless water heater in 2022 – Complete Guide

How to Vent a Tankless water heater is required for the proper operation of a gas tankless water heater. It is because it is burning explosive natural gas to heat the water. This, in turn, produces some harmful gases like carbon monoxide as by-products. Without proper venting, these gases will populate the space of your house and can be life-endangering.  Hence, extreme caution needs to be taken while installing the vents. Similarly, it would help if you had a certain level of knowledge before you can do so yourself.

How to Vent a Tankless Water heater

There are a number of things that you need to check to know what type of venting options you have.

Does your tankless unit come with single or double vent collars? If it comes with a double vent, you can use PVC schedule 40 on both pipes or cap one vent and use a concentric vent pipe on the other.

Measure the vent collars on the tankless to know which size of pipes you need. Mostly, it is in size of 3-5 inches, with the inner pipe being a 3-inch and the other one being of 5-inch diameter.

With a concentric vent, you get three screws to strap the pipe on the vent collar, while PVC schedule 40 comes with grease that you need to lay on PVC schedule 40 to fix it on the Vent collar.

Decide where to punch a hole for the vent. The vent should have a slight downward slope, so the exhaust does not return into the unit.

In the case of vertical or roof vents, set a cap to stop rain and debris from coming into the unit.

Let us go over a few points you should be aware of before we begin with how to Vent a Tankless Water heater. There are two ways to venting. These are power vent and direct vent.  A power vent uses the airflow around the unit, which could be air in your room where a tankless unit is situated. However, such a type of vent can become a problem if the room has bad airflow.

On the other hand, a direct vent uses two pipes, with one pipe being over the other. The outer pipe brings in fresh air to facilitate combustion while the inner pipe exhaust the by-product gases to the outside. There are two types of direct vent pipes used in a tankless water heater. Knowing which one to use is the most important to get the best results. They are as follow:

1.      Concentric Vent

A concentric vent uses a double vent pipe, with the outer pipe being PVC, and the inner pipe is of Stainless Steel.

It brings fresh air into the tankless unit through the space between PVC and Stainless Steel pipe. In contrast, harmful by-product gases of tankless water heaters are exhaust through the stainless steel pipe.

A regular gas tankless water heater, also known as a non-condensing tankless water heater, uses such type of venting. Stainless steel pipe is preferred because the unit’s by-product exhaust is extremely hot (around 150°C) and highly corrosive. It can corrode or rust regular steel and melt the PVC pipes.  Hence, it would be best to use a stainless steel pipe that is quite expensive but reliable.

2.      PVC Vent (Schedule 40)

A PVC Vent (schedule 40) is similar to a concentric vent in that it also uses dual venting pipes. However, unlike an inner stainless steel pipe, both these pipes are made of PVC schedule 40. You can see such a type of venting in a condensing tankless water heater, which is a gas tankless water heater variant.

PVC is used instead of stainless steel because a condensing unit even re-uses the exhaust hot gases and vapors to cool the water. This way, the heat of vapors is transmitted to the water, and they become cooler to 40° C. Such cold vapors cannot melt the PVC pipe; hence, you do not need stainless steel to vent them.

3. Horizontal vs. vertical venting

You can do the venting of the tankless water heater in two ways. Namely, a vertical way and a horizontal way. Vertically, a vent exhaust gases to the outside through the roof. Such venting needs you to install a top above it to prevent rain and debris from getting it. While horizontally, the vent goes through the wall to exhaust the gases outside.

At this moment, you are half a plumber yourself in terms of tankless water heater vents. Let us throw some light on some of the general knowledge related to venting that can save you from many troubles.

4. General knowledge for venting tankless water heaters:

Gas tankless water heaters require proper venting. However, if you have an outdoor tankless unit, you do not need to install a vent.

Venting must be such a way that they vent outside of your house.

The tankless water heater should have a separate venting from other appliances in your house. You cannot use a masonry chimney as a vent for a tankless water heater, which uses the natural rising of hotter air to exhaust the gases. Such vent cannot keep up with the tankless requirement of exhausting gases.

For a non-condensing tankless unit, venting should use concentric pipes with stainless steel pipes. The exhaust is extremely hot and can damage the PVC pipe. While, for a condensing unit, you can use PVC schedule 40 Pipes.

The vent should go on for the shortest distance. It is wiser to install a tankless unit in a space where it is closer to the outside. It could be in the attic or a wall whose other side faces outside as a longer distance venting increases the cost.

You can downslope the vent that would protect it from bringing back the flue to the heat exchanger.

Vent pipes need to be fixed on the collar of the unit. Never permanently seal or weld the vent pipe on the collar of the unit, as you may need to remove it in case of repair or maintenance.

Properly measure the collar of the unit before buying the vent. Buying a bigger size or longer length can only be a burden on the pocket.

Frequently Asked Questions

Can I use the existing vent for a tankless water heater?

No, you cannot use the existing vents, as they cannot support the exhaust capacity of a tankless water heater. Similarly, you cannot share the vents of a tankless water heater with other appliances of your house. It is because tankless exhaust contains harmful gases that can be a problem if they circulate in your house.

Do all tankless water heaters need to be vented?

No, this is not true for all kinds of tankless water heaters. It is commonly used in gas tankless water heaters as they use combustion gases to heat the water. Such a process releases some by-products like carbon monoxide. Such gases are the reason why you need a vent. You also do not need to vent if you buy an outside tankless water heater. Unlike gas, solar or electric do not produce by-products hence do not need venting.

 How much ventilation does a tankless water heater need?

A tankless water heater requires a 3-5 inches concentric or PVC schedule 40 vent pipes, which use direct vents or, in other words, double pipe exhaust. Where one pipe is over the other. You need to install a concentric vent with an inner stainless steel pipe and outer PVC in case of a non-condensing unit. At the same time, you can use PVC schedule 40 for condensing units.

Can you vent a tankless water heater with PVC?

Whether you can use PVC as a vent or not depends on the Tankless water heater model. You can use PVC schedule 40 for the condensing units or tankless with a double vent option. While for the rest of the indoor non-condensing units, you need to vent using a concentric vent pipe.

Conclusion

Venting, for the most part, is easy; the difficulty lies with knowing what to buy to get a worry-free life. This article gives you all the essential knowledge you need to understand How to Vent a Tankless water heater and know what you should look for in a tankless unit vent.


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