High-Efficiency Condensing and Non-Condensing Gas Tankless Water Heaters

Non-condensing tankless water heaters heat water on demand instead of storing it in a tank. When you turn on a hot water tap, cold water flows through a heat exchanger where a gas burner warms it to your set temperature. A properly sized exhaust gas vents through metal pipes, providing a continuous flow of hot water as long as you need it.

Benefits of Non-Condensing Tankless Units

Non-condensing units only heat water when you turn on a faucet, so you're not paying to keep 40-50 gallons hot all day. A. O. Smith's ADAPT® NC models are also backed by a 15-year limited warranty. 

How Non-Condensing Tankless Water Heaters Work

When you turn on a hot water tap, cold water flows into the unit and passes through a single heat exchanger. A gas burner heats the water as it moves through, and you get hot water coming out the other end. The leftover exhaust heat vents out through metal pipes at temperatures around 300°F or higher—much hotter than condensing models that recycle some of that heat.

Learn About High-Efficiency Condensing Gas Tankless Water Heaters

Venting for Non-Condensing Tankless Water Heaters

Non-condensing units need larger vent pipes to safely move that hot exhaust out of your home. A. O. Smith's non-condensing tankless models work with 2-inch venting, including commercially available concentric vent pipe (metal on the inside, plastic on the outside), giving installers more flexibility during setup.

Our professional installers will handle the venting to match manufacturer specs and local codes. This isn't something to tackle yourself—venting setup changes based on your home's layout, and doing it wrong creates real safety problems.

Non-Condensing vs Condensing Tankless Water Heaters

The main difference is how each type handles exhaust heat. Here's what sets them apart:

• Non-Condensing Models: Vent exhaust gas out right away using a single heat exchanger to warm your water, then release the remaining heat outside—simpler installation with lower upfront cost.
• Condensing Models: Pull some of that exhaust heat back with a second heat exchanger and put it to work heating more water, making them more energy efficient but costing more upfront.