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High Altitude and Gas Water Heaters

High Altitude and Gas Water Heaters

Natural gas is an excellent fuel source for hot water heaters . . . unless you live in high altitudes. But even if you live on a mountain, there are ways to modify your water heater so that it operates properly.

High Altitude means Less Oxygen

High altitude problems are not exclusive to gas water heaters, in fact, all gas appliances need to be modified to function properly. Water heaters are designed and manufactured to operate at sea level. Since the amount of oxygen in the air decreases with altitude, the air-fuel mixture also changes. With the decrease of oxygenated air, combustion is compromised.

When the balance of gas fuel and fresh air is correct, a consistent, steady blue flame emerges. Make any adjustments to the balance of gas and air, and the flame pattern also changes. In some cases the natural gas won’t burn at all. A properly balanced air-fuel mixture not only assists your water heater to operate efficiently, but also ensures a clean burn of the gas fuel.


Gas water heaters use a chemical reaction called combustion that creates both heat and light. In order for combustion to occur, 3 components must be present:

  1. Fuel  (gas)
  2. Oxygen (fresh air)
  3. Ignition (pilot light)

Once combustion takes place a byproduct of carbon dioxide (a harmless gas) is produced. If the supply of oxygen is inadequate, the combustion reaction does not properly occur, and carbon monoxide is produced. Without an adequate supply of air to support proper combustion, the amount of carbon dioxide is reduced, and in its place, carbon monoxide is produced instead.

Carbon monoxide is a colorless, odorless gas that is produced by the incomplete combustion of any fossil fuel (natural gas, coal, oil, and even wood). Carbon monoxide will prevent blood from absorbing oxygen, and it’s victims will be lulled into an unconscious state. It can be lethal, and is often called the silent killer.

We highly recommend having a carbon monoxide detector located near your gas water heater.

Less Oxygen means Less Fuel

Air provides the water heater with oxygen, and oxygen is needed to maintain the pilot and main burner flames. If combustion is not properly occurring in your gas water heater, it is likely because there is not enough oxygen to balance the fuel.
You may notice the following:

  • Yellow flame
  • Sooting on burner plate
  • Abnormal flame patterns (flame should be blue and steady)

Less Fuel means High Altitude Modifications

The oxygen in the air decreases the higher you are above sea level. This means that if you live in a high altitude area, you have less oxygen in your air. As a general rule, gas water heaters can function up to 2,000 feet above sea level without the need of being adjusted for high altitudes.

If a modification is necessary, it is done by adjusting the air-fuel balance. This modification will allow the water heater to adapt to the atmosphere change.

There are 2 options that can be done to modify you water heater for high altitudes. It is important that you only do one, NEVER DO BOTH.

  1. Derate the water heater – Replace the orifice in the main burner assembly. This main burner orifice controls the amount of fuel that is released into the combustion chamber. When the orifice size is reduced, the amount of fuel released is also reduced. The general guideline is to reduce the main burner orifice size by 4% for every 1,000 feet of altitude.
  2. Devalue the gas fuel – This must be done by your local gas utility company. Often gas utilities have already made the adjustment to their fuel if they service customers in high altitude areas.

Modifying your gas water heater for high altitude does not mean that your water heater is not operating properly. It is simply an issue with the atmosphere in which it is surrounded. By making a few adjustments, your water heater will be able to function at optimal levels.