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Gas Water Heaters That Don't Draw Air

Unlike electric water heaters, gas-powered heaters rely on an adequate supply of air to run properly. As the heater warms the water, the flame within the base of the tank draws air into the heater. The air flows through the tank and exits through a flue at the top. If the heater produces a puffing sound from the bottom of the tank when the burner is lit, the problem could be an inadequate supply of air. Exercise care in diagnosing the problem, however, as there are a number of related causes that are easy to overlook.
  1. Inadequate Ventilation

    • A shortage of air is a common problem when a water heater is installed in a small space, such as a utility room or closet. The problem is exacerbated if another component that uses air, such as a furnace or clothes dryer, is stored within the same area. A simple test is usually all that's necessary to determine if the confined area is responsible for the lack of air flow. Close the utility room door and allow the water heater to operate for a few minutes. As soon as the water heater starts to produce a puffing sound, open the door and a nearby window. If the puffing stops, the water heater is not receiving enough air. If the water heater is stored within a closet, you can replace the door with one that features louvers, or remove the door. If the water heater is stored within a room, consider replacing the room’s door with a louvered door.

    Flue Problems

    • Water heaters draw air through the lower portion of the tank. To maintain an optimum draft at the burner underneath the tank, water heaters are equipped with a flue at the top. If the flue is clogged, air cannot pass through the flue and the water heater will struggle to draw air into the bottom of the tank. Although clearing a flue is best left to a professional, you can test the flue quite easily. If the heater is in a utility room, close the door. Allow a few minutes to pass for the heater to develop a draft. Hold a smoking match or a lit incense stick about 1 inch away from the flue hat. The flue hat is located between the top of the tank and the bottom of the flue. If the flue draws smoke toward it, or if the flue pushes smoke away from the flue hat, the flue is probably not the problem. If the direction of the smoke doesn't change, contact a professional about cleaning the flue.

    Insulation Blankets

    • Insulation blankets are often used to reduce the utility bill. As the hot water sits within the tank, the heat gradually passes through the tank's walls. Once the water temperature falls below the thermostat’s setting, the water heater turns on and raises the water temperature back to the desired setting. An insulation blanket wraps around the water heater’s tank and is designed to minimize this heat loss. In some cases, the blanket can prevent the heater from drawing air. Consider removing the blanket if you suspect that this may be a possibility.

    Related Problems

    • It's easy to misdiagnose a defective thermocouple or a dirty burner as an air shortage problem. The thermocouple is the component that holds the pilot flame next to the burner. The burner is the component that ignites and heats the water. An old thermocouple may not produce a strong flame, or any flame at all, even if the water heater is drawing in plenty of air. The burner is equipped with several small jets around its edge. Dirt and debris tend to clog these jets and the burner will produce only a weak flame. Unless the burner is very old, you may be able to clean it with a vacuum or by passing a stiff wire through the jets to remove the debris. Turn the gas off before disturbing either the thermocouple or the burner.