Non-Condensing Tankless Water Heaters

What’s the difference between non-condensing & condensing tankless water heaters?

Non-condensing tankless water heaters have a heat exchanger (burner) that heats water as it flows through the unit. They vent hot exhaust gas which is why Navien non-condensing models are built with exhaust systems that tolerate high temperatures. Because the exhaust gas doesn't cool or condense inside the unit, non-condensing tankless water heaters don't need a drain.

Condensing tankless water heaters have a secondary heat exchanger that captures heat from the exhaust gas and uses it to preheat cold water before it’s fully heated by the primary heat exchanger. Because the exhaust gas loses heat and condenses inside the unit, condensing tankless water heaters require a drain and allow more types of venting material to be used.

Are non-condensing tankless water heaters better than condensing? 

It depends on your preferences:

Non-condensing tankless water heaters offer more flexibility for installation because they don’t require a drain. They’re also smaller than condensing models, and need minimal maintenance. Non-condensing tankless water heaters have an efficiency rating of 0.81 UEF, which is much more efficient than traditional storage tank water heaters.

Condensing tankless water heaters offer an ultra-high efficiency rating of up to 0.96 UEF, as well as higher flow rates. They’re also compatible with more types of venting material like PVC and polypropylene. But condensing tankless water heaters need a drain for the condensate, and annual maintenance is recommended.