The difference comes down to efficiency versus installation details.
| Non-condensing | Condensing | |
|---|---|---|
| Efficiency (UEF) | About 0.81–0.82 | About 0.90–0.98 |
| Venting | Metal: e.g. 4" Category III stainless (Takagi) or concentric (Rinnai) | Plastic allowed: PVC/CPVC, sometimes polypropylene |
| Condensate drain | Not needed | Required; a neutralizer is an option |
Which makes sense
Condensing units cost more but use less gas and often allow cheaper, more flexible venting. Non-condensing units can make sense where a metal vent is already in place. Your installer will look at the vent route and whether there is a drain nearby for condensate.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:Rinnai RE series non-condensing spec sheet (6/2022); Rinnai RX199iN product page; Takagi residential brochure (4/2023); Navien NPE-2 QuickFacts (NPE2-QF001). SD Water Heaters is not affiliated with any manufacturer; brand names are used only to identify products, and codes can differ by model, so confirm in your own manual.
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