Water Heater Combustion Air Requirements

Combustion air is necessary for any gas appliance to function. Appliances, such as a water heater, need a set amount of air for combustion. If there isn’t an adequate air supply, the pilot light and burner could get extinguished. A lack of it creates increased maintenance costs, poor heater operation and can give off dangerous amounts of carbon monoxide.

Water heaters burn liquid propane or natural gas. The burning of gasses from the water heater is known as combustion. It generates heat, moisture, and exhaust gasses. The ventilation system removes these products from the home, making it safe. Ventilation systems depend on the water heater installed.

Water heaters utilize a pipe or vent duct (flue or chimney) to remove these gasses from the outdoors. It can be plastic or metal, depending on the system. Water heater ducts generally lead outside or can go into a larger vent duct.

A water heater requires both proper venting and air supply for combustion to work optimally. It can be received through the air in the house or a vent pipe generating air from outside. If the air is low due to back drafting, clutter, or improper ventilation, problems soon occur.

A common mistake is that people assume any degree of air is enough. However, this is untrue. If the burner or pilot light continually goes out, a lack of combustion air may be the culprit.

How Much Combustion Air Do I Need?

To determine if there is an adequate supply of combustion air for your water heater, you need to factor in the following:

  • Ensure the room is big enough to provide adequate combustion air. There need to be 50 cubic feet of air/1,000 BTUs for the system to run in optimal condition. If a standard system needs 40,000 BTUs/hour, then you need 200,000 cubic feet of space. This is often the reason why people place water heaters in a basement or garage.
  • If the water heater is inside or outside the closet, the air must be vented into the area, usually with openings either on the closet door or the wall.
  • There are usually two vents for this purpose. A top vent should be 12″ from the ceiling with the bottom within 12″ of the floor. They also need to be the proper size (1 square inch per 1,000 BTUs). If the water heater is in an outside closet, it is 1 square inch per 2,000 BTUs.
  • Even if there is enough combustion air, clutter can create issues as well. If the heater cannot pull in an adequate amount of air, a problem could arise. A two-foot area around the water heater should be kept clear of any objects to keep the water heater at optimal performance.

Problems can also occur with commercial water heaters. If they are in a laundry room, the burner can suck in lint and other debris, causing the water heater to not function properly. Keep the area surrounding the water heater clean, and have it inspected regularly.

Do Gas Water Heaters Need Fresh Air?

As mentioned, an absence of an adequate amount of combustion air can lead to carbon monoxide poisoning. If you are concerned or suspect your heating system may be unsafe, ask everyone to exit the house. Then notify your local fire department.

The quantity required in any house is dependent on fuel type, meeting air requirements to ensure there is enough exhaust draft, and input BTUh rating of the equipment. A lack of proper combustion air in a house may have the following indicators:

  • Gas burner odors or soot. Tiny amounts of flame marks or soot at the gas burner can show an operating issue, but carbon monoxide may not be existent in the atmosphere.
  • Burn marks- This can be caused by blocked exhaust flues/improper venting.
  • Noise in the heating system or chimney when the water heater turns on, shuts down, or is starting.
  • Smoke
  • Carbon monoxide alarms going off

How Do You Correct This Problem?

Noise in the heating system or chimney when the water heater turns on, shuts down, or is starting. If the room is smaller than what it is supposed to be, it is called a confined space. Since homeowners will need to have combustion air coming in from somewhere, there are several options available.

heating system installation

A common solution is having the room receive air from the remainder of the house. Often, people accomplish this by creating vent openings in the furnace room, allowing it to be connected to other rooms in the house for fresh and adequate air to move through the area. This only works if the combined rooms meet the 50 cubic feet per 1,000 BTU/hour requirement.

Homeowners can also have a louvered door (this door has horizontal slats for ventilation). If it is louvered over the entire surface, it will work for ventilation as long as the water heater is lower than 175,000 BTU per hour.

Additionally, the furnace room can connect to the remainder of the house with two vent openings. Each vent must be 1 inch squared per 1,000 BT/hour of input of the collective gas appliances (meaning both furnaces if it’s in the same location and the water heater). Each vent needs to be a minimum of 100 inches squared.

One vent should be within 12″ from the space with the water heater, with the other found within 12 inches from the bottom. The smallest dimension per opening must be three inches. To ensure your water heater has adequate combustion air, make sure it is in a well-ventilated area. If it isn’t, find a way to vent it. Homeowners do not want carbon monoxide to build up in their homes.

Carbon monoxide has no odor and no atmospheric taste. Aside from a detector- which most houses need to have- homeowners cannot tell if it exists in their home, making it a silent killer. A lack of ventilation or clutter around the furnace and water heater can limit the airflow necessary for air combustion, having some deadly consequences if not addressed.

If your area is too small, add vents, open up the room, or add a louvered door. All these things will help with the airflow necessary for proper combustion to occur. It will keep your home and family healthy.

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