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Hot Water Heater Vent Pipe Size

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Every home has a water heater. A water heating system has become nothing short of a necessity today. And it is vital that you, the homeowner, know all the basics of its structure and functions.

A heater uses intricate designs to ensure that you get a hot shower whenever you desire.

Every heater needs to relieve itself of the exhaust gases that it produces. The heater uses a specially designed venting system to complete this process. Let’s take a look at the specifications for water heater venting.

What is a Water Heater Vent Pipe?

What is a Water Heater Vent Pipe?

A water heater vent pipe is the affiliate drainage system for a heater. It acts as a pathway for exhaust gases to leave the system and enter the atmosphere.

Any heater, be it powered by gas or electricity, has to hold a venting system. That system is made out of a series of pipes that conduct the gases outside.

Every water heater system uses fuel of some kind to generate heat. Once this heat is generated, there is a systematic release of exhaust gases. Now, these gases need to be released out into the atmosphere as soon as possible.

The heater uses chimneys to facilitate the transfer of gases from inside the house to outside. Vents are essential because they prevent the building of additional pressure inside the storage tank. Such hyper pressurized containers can be risky and prone to explosions.

A vent pipe, also called a duct, is connected to the heater. It generally runs along the walls of your house. There are multiple types of water heater vents – direct vents, power vents, and chimney flues are the most commonly seen.

A chimney can run along the walls of your house and dispense the gases through the roof. Similarly, a direct vent generally goes through the wall directly, whereas a power vent runs through the width of the wall horizontally.

Electricity-powered water heaters generally use power vents (see also ‘ Power Vent Water Heater: Why You Should Buy One ‘). These are vents placed horizontally across the wall. They also have a blower – a fan – set in the vent to propel hot exhaust gases through the horizontal duct.

Does a water heater vent pipe need to be double-walled?


Vent Pipe with double shield

That is a tricky question to answer. Vent pipe materials have to be durable and robust because they have to conduct hot gases. Therefore, most of them are made of steel.

However, some new varieties of vent pipes are also made of PVC. Generally, vent pipes are of two types – single-walled and double-walled. As their names suggest, these vent pipes have one and two layers on them, respectively.

Conducting hot gases makes the pipes warm. More often than not, vent pipes come in contact with the walls of the house. If the walls are made of wood, and the hot pipe comes in constant contact with them, combustion is possible.

Keeping the vent pipes a small distance away from the walls is preferred to prevent any such mishaps. Single-walled vents are prone to getting very hot and are therefore advised to be at least 6 inches away from the wall’s surface.

On the other hand, a double-walled vent has an extra layer around its conducting layer. Therefore, you can keep it 1 inch away from the wall. If you find that the vent has to pass through a wooden surface, then ensure that you cut out any parts that may come into contact with it.

You can also use a double-walled vent pipe for such cases to be on the safer side. Most safety precautions related to the installation of vent pipes are printed on the product’s packaging itself.

It would be best if you employed professional handypersons or plumbers to install the vent pipes in your home, as they would do the job swiftly and inexpensively.

How do you secure a water heater vent pipe?


secured vent pipe

A water heater vent pipe carries hot exhaust gases from the heater and dumps them outside the house, eliminating your heater of any risks.

In this process, the pipe is likely to get hot. It would help if you found solutions to this and prevented the hot pipe from scalding anyone or burning a part of your house.

The most straightforward solution is to use double-walled vent pipes in all water heating systems. They are suitably built to withstand the heat and would prevent damage to your house. However, if these pipes are not available, you can ensure a few other specifications to avoid mishaps.

For instance, you could use a direct venting system. This kind of heating system needs the least amount of venting. It makes your water heater a breathing system, as it operates outside air to generate heat and then exhales all the exhaust gases out. With adequate airflow through your vents, the direct vent system reduces the risk of anything catching fire.

Alternatively, you can use a power vent system, which is even safer than a direct vent. A power vent runs on electricity and contains a tiny fan called a ‘blower’ at the beginning of the duct. The blower pushes the hot gases out of the vents and into the atmosphere. Additionally, constant propelling from the blower ensures that the vent pipe does not get too hot.

Lastly, the opening of the vent pipe can be a significant source of hot air and can therefore be very hot. Therefore, most local building guidelines ask you to keep the mouth of the vent at least 1 inch away from any combustible material. Checking your local building guidelines or codes is an essential aspect of having a safe water heating system.

What are the guidelines given by the government for venting a water heater?

Most local governing bodies will assert a codified set of guidelines or laws that you must abide by and adhere to. These guidelines are specific to different gadgets.

Good venting guidelines for Gas-powered water heaters

venting guidelines

Water heating systems must be vented with ducts of appropriate size and height. Also, citizens should ensure that these pipes produce an adequate draft for the exhaust to fall out of the residence.

If the vents are not checked before installation, they may spill dangerous flammable and poisonous gases into the house itself. Lastly, the vent must be installed by a qualified person who knows all the tricks of the trade.

Some local codes also advise homeowners to install carbon monoxide detectors near their heaters. Sometimes, exhausts can rush into the building because of some error in the venting and rage havoc. It is better to have sensors that can sound the alarm for toxic gases like carbon monoxide.

All venting must be at least 6 inches away from surfaces in the house. Therefore, you will notice that most heaters have their vents a considerable distance away from walls. That is done to prevent the walls of the house from catching fire from the hot vent pipes.

Lastly, the code urges citizens not to merge vents between a gas-powered device and a power-vent appliance. All the above guidelines are a part of the National Fuel Gas Code for the USA. You can alternatively refer to the guidelines mentioned on product packaging.

Should the water heater vent pipe turn hot?

Yes. Even a double-walled metal or PVC duct is susceptible to the heat of exhaust gases. A water heating system uses elements in the air to generate heat and then uses that ignition to warm the water in the storage tank.

The heat that the water heater generates is converted into residual gases like carbon monoxide, which have to be thrown out of the house. These gases are poisonous and cannot stay in the same small space as the heater. In transferring these hot gases outside, the vent pipe turns hot.

Also, venting is done on the scientific principle that hot air rises upwards. Therefore, the hot gases rise through the vents, casually heating them in the process. Moreover, most vent pipes are made of metals like steel, which is a good conductor of heat. Therefore, vent pipes are supposed to turn hot.

If you have your heater’s thermostat set to 120 degrees F, your vent pipes can have a temperature of over 300 degrees F at the end of the day. Moreover, if your venting pipe is turning hot, it means that the pipe is conducting hot gases in the prescribed manner, therefore doing a good job. So, you do not need to worry if the vent pipe turns hot.


The venting attached to a water heater system is an integral part of the entire process. You cannot have a stable and functioning water heater without a good venting design.

Most commonly, metal duct pipes are used for this purpose. However, with new tech emerging constantly, homeowners have started opting for PVC vents now.
You have to be careful while installing vents on your heater. It is a delicate matter, and even the slightest of errors can prove to be a disaster.

Hot pipes are known to ignite the wooden walls surrounding them, and to prevent this, most local governing bodies have issued special codes and guidelines. Following these guidelines and taking expert opinions for installation are two ways to avoid any mishaps.

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Charlie Hardcastle


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