Gas hot-water heaters with power vents are vented using PVC pipe through walls. They do not require the horizontal vents installers use with naturally vented gas water heaters. An exhaust fan provides the power to move the undesirable gases out of the home.
Naturally vented water heaters use the fact that warm air is less dense than cooler air to create a vacuum to pull exhaust gases away from the burner. This chimney effect is the same process that exhausts smoke from a fireplace. As of 2015, natural vents do not always work well. Homes are more tightly constructed than in previous times, making the natural draft more difficult to maintain. In multistory homes, the natural vent needs to travel through each story to reach the roof to exhaust the gases.
The addition of a power vent to a water heater allows venting through the wall without passing through the construction above the water heater. Vent pipes can make 90-degree turns and horizontal runs without endangering the home occupants.
Disadvantages of power vented water heaters include the need for electricity for operation, the noise of the fan, increased cost and the need to replace the air the appliance exhausts. In some locations, building codes require inspections of power vented appliances after installation.