Condensing Tankless Water Heaters

As water is heated, the burner creates hot exhaust gas. Condensing tankless water heaters use the heat from exhaust gas to preheat cold water, making them very energy efficient. As it cools, the exhaust gas condenses and turns into water vapor which eventually flow out to the drain.

Yes, condensing tankless water heaters need a drain for the condensation water that forms in the secondary heat exchanger.

Condensing tankless water heaters require venting because they burn gas (natural gas or liquid propane) to heat the water. Because condensing tankless water heaters reclaim heat from exhaust gas using a secondary heat exchanger, less expensive venting materials (like PVC) can be used.

Condensing tankless water heaters can be vented through a wall or the roof, up to 75 feet with 2” vent pipe. Because condensing tankless water heaters have relatively cool exhaust gas, you can use 2” PVC or rigid/flexible polypropylene venting. Condensing tankless water heaters cannot share venting with other appliances, and cannot be vented through a chimney.

When propane or natural gas is burned as fuel, the combustion process creates carbon dioxide and water vapor. As the vapor cools and condenses it absorbs the CO2 and forms carbonic acid, which makes the condensate acidic. Navien condensing tankless water heaters create condensation with an acidic pH of 3 - 5.

PVC and CPVC are safe drain line materials for tankless water heater condensate because they are corrosion resistant.

Condensate from a tankless water heater comes out through the condensate drain at the bottom of the unit which connects to a drain line made of corrosion-resistant material such as PVC or CPVC.  A neutralizer is used to bring the acidic levels back up to neutral levels.  This condensate must be drained properly as per local codes, some options are to a laundry tub, utility sink or floor drain. When there is a long distance between the water heater and a drain, a condensate pump can be used. 

Local codes and regulations may require neutralizing the condensate before it drains. To neutralize the condensate, install a neutralizer in the drain line and replace the neutralizing agent as needed. Navien provides both residential and commercial neutralizer kits as well as replacement media. Find more information about neutralizers including downloadable user guides on our accessories page.

Condensing tankless water heater installation is best done by a licensed professional plumbing contractor because it involves disconnecting and reconnecting gas lines. Venting and wiring also require professional expertise to ensure the installation meets building codes. You can learn more about installation cost factors and find an installer in your area.

Condensing tankless water heaters operate at up to 96% efficiency, meaning 96% of the consumed energy is used to heat water and only 4% is lost. 

You'll often see condensing tankless water efficiency described in terms of UEF: Uniform Energy Factor. UEF is a standardized measure where a higher value means better energy efficiency. A UEF rating of 0.96 means 96% energy efficiency.

Condensing tankless water heaters need to be descaled (aka “flushed”) about once a year to remove mineral deposits and maintain optimal efficiency. Learn about your options for descaling a tankless water heater, including DIY instructions and the benefits of hiring a professional for annual cleaning and maintenance.

Condensing and non-condensing tankless water heaters require the same amount of regular maintenance, which involves cleaning inlet filters, the air filter, a visual inspection and descaling. Maintenance details for each model can be found in the user’s manual which you can download here. 

All water heating products require routine maintenance, and condensing tankless water heaters don’t require any more maintenance than tank style water heaters. Tank water manufacturers recommend flushing the tank every 6-12 months as well as inspection and cleaning of the burner chamber, pilot assembly and air intake.

No, condensing tankless water heaters don’t have a pilot light. Instead, the water heater has an internal igniter that activates when hot water is needed.

Compared to both conventional tankless and tank-style water heaters, condensing tankless water heaters are much more energy-efficient and use less energy, lowering energy bills and reducing your carbon footprint. Learn more about exactly how much energy and money condensing tankless water heaters can help you save each year.