Free standard shipping on orders over $149.97
Condensing vs non condensing tankless water heater: it’s the biggest choice after fuel type. Condensing units squeeze extra heat out of the exhaust; non-condensing units are simpler and cheaper.
A non-condensing tankless water heater has one heat exchanger. Exhaust leaves hot, around 300°F or more, so a lot of heat goes up the vent. A condensing tankless water heater adds a second heat exchanger that pre-heats incoming water using that exhaust heat. The exhaust cools to roughly 100–140°F, water vapor condenses and the unit reaches efficiencies above 90%.
| Condensing | Non-condensing | |
|---|---|---|
| UEF | About 0.90–0.97 | About 0.80–0.83 |
| Vent material | PVC, CPVC or polypropylene | Category III stainless steel or approved special vent (indoor) |
| Vent cost | Lower | Higher |
| Condensate drain | Required | No |
| Neutralizer | Often required | No |
| Unit price | $300–$800 higher | Lower |
| Outdoor models | Available | Common and popular |
| Rebate eligibility | Often eligible | Rarely eligible |
Condensate from gas combustion is mildly acidic (often pH 3–5). Most installations route it through a condensate neutralizer, a small cartridge of limestone or similar media, to a floor drain, laundry standpipe or sink tailpiece. If no drain is nearby, a condensate pump lifts it. The drain must not freeze, which matters in garages and outdoors. Your local code and the manual specify requirements.
A blocked tankless water heater condensate drain triggers error codes on most condensing models.
Condensing lines include the Rinnai Sensei RU/RX series, Navien NPE-A2/S2 series, Rheem IKONIC and Prestige, Noritz NRCP and Takagi T-H3. Non-condensing lines include the Rinnai V series, Rheem Performance (RTG) series and Noritz NRC series. Always confirm on the specification sheet.
Never mix vent materials or use PVC on a non-condensing unit. Vent material, diameter, maximum length and terminal clearances come from the manufacturer’s manual. Read our tankless water heater venting guide.
Every gas listing shows whether a unit is condensing, its UEF and its vent type.
A gas tankless water heater with a secondary heat exchanger that captures heat from the exhaust. The exhaust cools enough for water vapor to condense, which releases more heat and raises efficiency above 90%.
Yes. It produces acidic condensate that must be drained to a floor drain, sink drain or condensate pump according to code, usually through a neutralizer.
Many manufacturers and local codes require one to protect drains and septic systems from acidic condensate. Check your installation manual and local code.
Only if there is no drain below the unit. A small condensate pump lifts the condensate to a drain. It needs a power outlet.
This guide is general information for U.S. homeowners, not professional advice. Gas, electrical and venting work must follow the manufacturer’s instructions and local codes, and in most areas requires a licensed plumber, electrician or gas fitter and a permit. Specifications and prices change; always confirm details on the product page and in the installation manual.
