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You are: Home > FAQs > Venting Information

By: Jordan Wilcox

What is venting and why do I need it?

Gas powered tankless water heaters and other appliances that rely on combustion for energy create harmful exhaust gases at varying temperatures. Most of these appliances are installed indoors so it is obvious the exhaust fumes need to somehow be moved outdoors. Vent pipe is a conduit through which exhaust gases are moved outdoors.

There are many different types of vent pipe depending on what type of appliance is being vented. For our discussion we are going to focus on two types: Type B Vent and Special Gas Vent, as they are the only two types of vent relevant to tankless water heaters. We will discuss the difference between these two in the next sections.

You need a venting system because without it your house would be liable to burn down and/or create a very dangerous environment with toxic gases. Exhaust gases range in temperature from 250° F (very efficient) to upwards of 1000° F. The combustion point for standard non-chemically treated framing wood used to build homes is 575° F. The exhaust from most tankless water heaters does not get that hot, the primary concern are the fumes which can be fatal.

Type B Vent

Type B Vent is made out of aluminum and is relatively inexpensive. Type B Vent must be vented vertically because it relies on natural draft to move the exhaust outdoors. Type B Vent is not sealed gas tight and there is actually open space where the appliance transitions into vent pipe. The hot air entering the vent pipe creates a chimney effect, or natural draft that moves the gases outdoors.

Special Gas Vent

Special Gas Vent, also known as Category III is made out of AL29-4C stainless steel and relatively expensive. Unlike B Vent, Special Gas Vent is sealed gas and liquid tight. Exhaust fumes are actually pushed through the system by a fan in the tankless water heater. Special Gas Vent can be vented vertically or horizontally; you will need to reference your owners manual or our product page to determine the requirements and limitations.

Vertical or Horizontal?

If your tankless water heater requires Type B Vent, then you have to vent your heater vertically. Some of the tankless water heaters do allow you to install a blower (basically a fan that pushes the exhaust through the pipe) which allows horizontal venting with Special Gas Vent.

If your tankless water heater requires Special Gas Vent then you can vent vertically or horizontally. In most cases you will want to vent horizontally because it requires less vent pipe and is therefore less expensive. The only exception is if your tankless water heater is being installed in your attic; in that case it requires less pipe to go straight out vertically.

For horizontal venting we carry the 4CGSWHVK vent kit by Metal-Fab that works with all Takagi and Rheem tankless water heaters. This is the most cost effective and convenient way to vent your tankless water heater.

Planning Your System

Once you decide where to install your tankless water heater, it is time to decide how to run your pipe. Your goal is to create as straight a run as possible to save money. More often than not there will be obstructions in the way that will need to be avoided. This is where the 45° and 90° elbows come into play. Start taking measurements to get an idea of how much pipe you will need. It is a good idea to draw a diagram with measurements to each point. While creating this diagram, you need to consider the clearances of the vent pipe. This information is provided on our site and in the technical documentation offered by Metal-Fab. Clearance refers to the distance from the outer edge of the vent pipe to any combustible material (anything that can catch on fire).

Venting Components

A vent system includes any number of pieces of vent pipe joined together. There are many different types of venting components that we will discuss next, but first we need to discuss why we carry the Metal-Fab line of vent products exclusively. Metal-Fab is unsurpassed in the vent industry in quality and customer service. The Metal-Fab line of Special Gas Vent (Corr-Guard) features one-piece silicone gaskets (to ensure a gas and liquid tight connection for your safety) and the easiest connection system in the industry they call Snap-Lock® (see picture below). Now we will discuss the different type of components that will be incorporated into your vent system.

Straight Pipe Lengths

 

Straight pipe lengths are the bread and butter of your vent system. Straight pieces will represent the majority of your total system length. They are available in different lengths ranging from 6 inches up to 3 ft. There are longer lengths but we only set up to 3 ft lengths because they can be shipped via UPS and FedEx without damage. In your long straight runs, you will want to use the longest pieces possible because they are more economical.

 

Appliance Adapters

Appliance adapters are used to connect your tankless water heater to your vent system. The adapter attaches to what is called the "flue collar" on your tankless water heater and serves as a connection piece to your vent system.

Variable Straight Lengths

 

As their name implies, variable straight lengths are adjustable in length. A variable length piece will almost always be necessary because the chances of your straight pieces coming to exactly the right length are very slim. The amount of variance ranges anywhere from 3 inches to around 16 inches.

 

Elbows

 

Elbows are used to change the direction of your vent system. To avoid an obstruction, two elbows will usually be used: one to steer out of the way, and the other to get back on course. There are 45° and 90° elbows available.

 

Increasers / Reducers

 

Increasers and reducers are used to transition your vent pipe to a different diameter. For example, if you need to increase the size of your pipe from 3 inches to 4 inches, you would use an increaser. Living at high elevations can sometimes require a larger vent diameter; check the owners manual for your tankless water heater for more details.

 

In-line Adapters

 

In-line adapters are like an in-line coupler you would use to connect two 10 ft pieces of phone cable. In-line adapters will have either two male or two female ends and are usually relatively short in length.

 

Drains

 

Drains are only applicable to special gas vent. Because tankless water heaters are so efficient, they produce condensate in the exhaust gases. If you were using B Vent with a tankless water heater that produces condensate, it would accumulate and then drip all over your floor causing water damage (fumes would also leak out which is a bigger issue). Special gas vent is sealed liquid tight to prevent this build-up from leaking out. The condensate cannot remain in the vent system because if enough were to build up, the weight could bring down your system. The condensate also cannot leak back into the tankless water heater; therefore horizontal runs need to slope away from the heater. Drains are also attached at tees which are used when transitioning from a horizontal to a vertical run.

 

Supports / Guides

 

Supports and guides are pretty self-explanatory. They are used to support the weight of your vent system. They need to be used in certain increments usually every 3 to 5 ft when running horizontally.

 

Roof / Wall Penetrations

 

Roof and wall penetrations are used to safely move your vent system through combustible materials. If the clearance required by your vent pipe is 2 inches, you don't want to have to cut a hole in your wall that has 2 inches of clearance all the way around, especially if this is an exterior wall. Penetrations provide a buffer so that there will be no danger of fire.

 

Tees / Wye's

 

Tess and Wye's are used to transition from a horizontal run to a vertical run. If using special gas vent, a drain should be used in conjunction with a tee.

 

Terminations

 

Terminations are the final piece in your vent system. If venting vertically you will have a vent cap which is pictured here. When venting horizontally, there are a few different types of pieces, but all serve the same purpose: to expel the exhaust into the outdoors.

 

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