If you live in a high altitude area you may have noticed that your gas water heater isn't working properly. Natural gas is an excellent fuel source for water heaters, but they need modifications to work in areas of high elevation.When a water heater is manufactured it is designed to work at sea level. At higher altitudes the air-fuel mixture is out of sync since the amount of oxygen in the air is lower. All gas appliances are affected by high altitude, but it is possible to make modifications to compensate for the lack of oxygen in the air.The higher the altitude, the less oxygen is in the air, which compromises combustion. A consistent, steady blue flame burns when there's the proper balance of fresh air and gas fuel. However, the flame pattern changes when any adjustments are made to this delicate balance.How Gas Water Heaters Heat WaterA chemical reaction called combustion takes place within the water heater to heat the water. Combustion creates both light and heat, but in order for it to take place, 3 things must be present:Fuel - In the case of a water heater, the fuel is natural gas.Oxygen - Fresh airIngnition - The pilot lightThe Oxygen Supply and CombustionThe higher you are above sea level, the less oxygen is within the air . . . therefore, when your home is located within a high altitude area, there will be less oxygen in the air. When there is less oxygen in the area, the chemical reaction of combustion can produce carbon monoxide, which is a harmful gas. Correct air-fuel mixture - a harmless gas called carbon dioxide is produced as a byproduct of combustion.Inadequate supply of oxygen - The combustion reaction is compromised, and less carbon dioxide is produced. However, carbon monoxide is also produced. Carbon monoxide is frequently called the silent killer because it's a colorless, odorless gas. It's a byproduct of incomplete combustion, and it can occur with any of the fossil fuels. Coal, oil, natural gas and even wood can create carbon monoxide if combustion isn't properly occurring. Carbon monoxide can be lethal since it prevents blood from absorbing oxygen. Those who are affected by carbon monoxide poisoning will simply be lulled into an unconscious state. There are detectors that can alert you when danger is near, and they should always be installed near a gas water heater. When the Air has Less OxygenOxygen is necessary for the pilot light and main burner flames. If the air is "thin" and has less oxygen, combustion is most likely not properly taking place. In other words, the air-fuel ratio is off since there isn't enough oxygen to properly balance the fuel. If your water heater isn't getting enough oxygen, you'll see the following signs: Soot on the burner plateYellow flameAbnormal flame patterns (the flame should burn steady and be blue in color)High Altitude ModificationsIn most cases a gas water heater will be able to operate properly up to 2,000 feet above sea level. However, if you are above 2,000 feet you'll need to make some modifications.A gas water heater can be adapted to atmosphere changes by adjusting the air-fuel balance. There are 2 options to make these adjustments:Devalue the gas fuel - You'll need to contact your local gas utility company to do this for you. In fact, you may find that they have already made the adjustment.Derate the water heater - If your gas company has not devalued the fuel, you can replace the main burner assembly orifice. This orifice controls the amount of fuel released into the water heater's combustion chamber. Reduce the orifice size and you reduce the amount of fuel released. As a general guideline, for every 1,000 feet of altitude, reduce the orifice size by 4%. CAUTION: Never do both of these methods.If your gas water heater isn't working properly in an area of higher altitude, it doesn't mean that something is wrong. The issue is most likely with the atmosphere. By making the necessary modifications your water heater will be able to safely deliver your household with hot water.