Home Depot, Lowe's and Wayfair.com sell high altitude water heaters. The manufacturer optimizes these units so the fuel burns at the correct gas to oxygen mix. While certification is important for all water heaters, uncertified on-demand gas water heaters do not always perform correctly at high altitudes.
Most homes use approximately 20 gallons of hot water daily per resident. While on-demand water heaters conserve energy, they are not practical for all homes. Most require a minimum flow before they start heating water, so low-flow uses, such as shaving, do not cause them to heat. Gas tankless water heaters work well at altitudes below 4,000 feet, but begin to lose approximately 4 percent efficiency for each additional 1,000 feet in elevation. Altitude does not affect electric tankless models.
In the United States, storage water heaters are the most common types of units in use. These devices heat the water to the set temperature using a flame or electric resistance element. Natural gas and propane are the fuels most homeowners use unless they have an electric water heater. While the higher altitude lowers the boiling point of water, water heaters generally store water at temperatures at approximately 130 degrees Fahrenheit, so the reduction in boiling point for tank-style heaters is not a problem.