Because all gas water heaters perform a similar task, it can be easy to fall under the mistaken belief that they all operate in the same way. Yet in fact, there is quite a lot of diversity within the world of gas water heaters--especially where venting options are concerned. If you would like to improve your knowledge of water heater mechanics, read on. Here are three different types of water heater vents.
An atmospheric vent is the simplest type of water heater vent. It consists, essentially, of a pipe leading from the combustion chamber up through the house and out the roof. Because the exhaust gases being generated by the burner are hot, they naturally rise upward and exit the house. In the process, they create a vacuum at the base of the vent; this vacuum acts to draw fresh air into the combustion chamber from the surrounding room.
A water heater with a direct vent differs in a number of ways. For one thing, it does not draw combustion air from the surrounding room. Instead, it relies on a special type of pipe system. Inside of the exhaust pipe that carries combustion fumes out of the home is a second pipe of smaller diameter. This pipe is used to draw air from outside of your home into the water heater.
A direct vent also integrates what is known as a draft hood. This is essentially an extra-wide opening at the end of the exhaust flue directly above the water heater. The idea of the draft hood is that it helps to pull additional air into the outflow pipe, thus helping the exhaust gases exit the home more quickly. It also eliminates the potentially dangerous scenario of "backdrafting," which can happen if an atmospheric vent becomes misaligned from the top of the water heater.
Power vents go one step farther than even direct vents. They incorporate a mechanical fan to aid them in moving exhaust gases out of the home. By powering the movement of these gases, a power vent allows the water heater to be installed virtually anywhere in the home. In other words, the exhaust pipe does not have to pass all the way up through the roof. In fact, it does not even have to be vertically oriented. In many cases, the easiest way to orient a power vent is horizontally.