What Is an Atmospheric Water Heater? A Quick Guide [Video]

By Mengning Heil

October 1, 2021

Water Heater Tips

Reading Time: 4 minutes

To properly answer the question “what is an atmospheric water heater,” we need to cover the basics first.

Natural gas is readily available in most homes and is a cheap source of energy. If your house runs on natural gas, it’s likely you have an atmospheric gas water heater, or what some call an atmospheric vent water heater. But how can you tell if you have an atmospheric water heater? What are they and how do they work? Watch the quick video and then keep reading.

What Is an Atmospheric Water Heater?

An atmospheric water heater is a type of gas-powered storage-tank water heater. What sets an atmospheric water heater apart is the way that it vents. All gas water heaters work by burning fuel to heat up the water. When the fuel burns, the exhaust needs to be taken out of the house. In an atmospheric water heater, those gases are vented out of your house through a large metal draft pipe at the top of the tank. Since hot air rises, the gases lift up and out of your house. In the process, the air in the atmosphere is naturally drawn into the vent. Therefore, it’s called an “atmospheric” water heater. 

How to Know if I Have an Atmospheric Water Heater?

You can identify a gas atmospheric water heater by 1) a yellow or black gas line with a gas shutoff valve running to the burner and 2) the presence of a metal pipe for exhaust ventilation on top of the tank. This large, aluminum pipe creates a natural draft that pulls the exhaust out, whereas other models may have a black fan connected to a plastic pipe that propels the exhaust out of your house. 3) The gap between the vent pipe and the tank where the air from the atmosphere is pulled in.

Parts of a Gas Water Heater

Understanding the important parts of a gas water heater can help you get to know your atmospheric water heater!

The tank “water in-water out”

Cold water from your water source enters the tank from the cold water pipe and is sent down through the dip tube to the bottom of the tank. The dip tube prevents the cold water from diluting the hot water already in your tank. Once the water is heated, it naturally rises to the top of the tank, exits through the hot water pipe at the top of your tank and is distributed to the rest of your house. The inside walls of your water heater tank have 2-3 inches of insulation and are lined with glass on the inside to protect the lining of the tank from corrosion. 

Heating the water

When your water heater senses cold water, a burner kicks on to heat the water. This burner is connected to a gas line equipped with a gas shutoff valve. This controls the flow of your gas line – important when doing repairs on your tank. The gas line feeds to the gas regulator which has a thermostat you can control from the outside to adjust your water temperature. 

Expansion tank

Have you noticed a small tank connected to the top of your water heater? That tank is an expansion tank, and it’s crucial for your safety. When the cold water in your water heater tank heats up the water expands, creating more pressure. An expansion tank helps regulate the pressure in your water heater and water pipe system. In many jurisdictions, an expansion tank is required to be installed with the water heater. 

Pressure relief and drainage

All storage tank water heaters also have a pressure relief valve to regulate pressure and hot air within the tank. Anytime pressure or hot air builds within the tank, the pressure relief valve automatically opens to regulate the tank and keep it stable. (DO NOT for any reason cap off your pressure relief valve. The pressure will continue to build within the tank and will eventually explode.) On the side of the tank, there should be a drainage valve used to drain the water out of the tank for repairs and periodic maintenance. 

pressure relief valve
pressure relief valve


Okay. So we know gas water heaters burn gas to heat your water. However, we also know that whenever we use gas, toxic exhaust needs to be safely vented away from any indoor living space. The burner at the bottom of your tank has a chimney or “flue” that runs through the inside of the tank and connects to an exhaust pipe outside of your tank. When the burner turns on, the pipe gets hot and creates a natural draft by pulling air through the space at the top of the heater which then also pulls the carbon monoxide and exhaust out of the house. 

what is an atmospheric water heater
a large metal draft pipe vents toxic exhaust away from your indoor living space

Benefits Of Atmospheric Gas Water Heaters 

Gas water heaters are cheaper overall than most water heaters. Electric water heater units cost less upfront but are typically more expensive to run monthly. A tankless water heater may save you roughly $100 a year in monthly costs but the units themselves are up to three times more expensive than tank water heaters and the initial cost to convert your system to tankless is more expensive than replacing your regular tank water heater. Overall, gas water heaters are cheaper than other water heaters and with proper maintenance should last you anywhere from 10-14 years. 

And there you have it: your very own crash course on gas atmospheric storage tank water heaters! 

Need water heater repair in Rockville? Contact Heil Plumbing today to connect with an expert plumber Rockville, MD! Live in the Baltimore-D.C. corridor but not in Rockville? With offices in Rockville, Jessup, and Timonium, MD, we have you covered.

Heil Plumbing is a family-run company owned by a third-generation master plumber. We provide a full range of plumbing services throughout the Baltimore-D.C metro area. Whether you need toilet installation and repair, leak detection and pipe repair, faucet repair and installation, drain cleaning, or water heater repair we’re here for you!