Quick Answer: Choose condensing for most gas tankless installs — it reaches a 0.93–0.97 UEF (versus 0.81–0.82 for non-condensing) and vents through PVC pipe costing roughly $3–$6 per foot instead of the $18–$35-per-foot stainless steel non-condensing units require. Choose non-condensing only when the unit mounts right beside a short existing metal vent, where its lower unit price isn’t erased by venting cost. The decision comes down to vent-run length and material cost, not just the sticker price on the box.
Both types burn natural gas or propane and both deliver on-demand hot water, but they extract heat from the exhaust differently — and that one difference cascades into venting material, install cost, and how much you pay to run the unit for the next 20 years.
Last updated September 4, 2026: reconfirmed the 0.93–0.97 vs. 0.81–0.82 UEF split and the $3–$6 PVC vs. $18–$35 stainless venting-cost figures against current industry install-cost data — no changes needed.
Condensing vs non-condensing at a glance
| Factor | Condensing | Non-Condensing |
|---|---|---|
| UEF efficiency | ~0.93–0.97 | ~0.81–0.82 |
| Venting material | PVC (Category IV) | Stainless steel (Category III) |
| Venting cost | ~$3–$6 per linear foot | ~$18–$35 per linear foot |
| Typical unit price | Higher upfront | ~$140–$800 less upfront |
| Condensate drain needed | Yes | No |
| Exhaust temperature | Cooled below dew point | Hot, uncooled |
| Best for | New installs, long vent runs, whole-home | Short run beside existing metal vent |
By the numbers
- 0.93–0.97 vs. 0.81–0.82 — UEF efficiency of condensing versus non-condensing gas tankless units. — ENERGY STAR / DOE efficiency ratings
- $3–$6 vs. $18–$35 per linear foot — installed cost of the PVC venting a condensing unit uses versus the Category III stainless steel venting non-condensing units require by code. — industry install-cost data
- $400–$800 — typical total installation savings from choosing PVC over stainless venting on a standard residential run, often enough by itself to offset a condensing unit’s higher sticker price. — industry install-cost data
Why condensing costs less to install (usually)
Non-condensing units exhaust flue gas hot enough that code requires expensive Category III stainless-steel venting — commonly $18–$35 per linear foot installed. Condensing units cool that same exhaust below its dew point in a secondary heat exchanger, recovering extra heat and dropping the exhaust temperature low enough to vent through ordinary PVC, at roughly $3–$6 per foot. On a typical 10–20 foot run, that gap alone is often worth $400–$800 — frequently more than the price difference between the two unit types. That’s the same math behind Rheem’s retail lineup: the non-condensing Performance Plus undercuts the condensing Performance Platinum by roughly $140 on the unit, but an indoor Performance Plus install needs stainless or concentric venting that can erase that saving fast — mounting it outdoors instead is the one case where the non-condensing unit stays ahead on total cost.
The tradeoff: condensate drainage
Condensing’s efficiency gain isn’t free of its own plumbing. Cooling exhaust below its dew point produces a small stream of mildly acidic condensate that has to go somewhere — a floor drain, a condensate pump, or a neutralizer cartridge that raises the pH before it hits your plumbing. It’s a minor, low-cost addition in most installs, but it’s a wrinkle non-condensing units simply don’t have, since their exhaust never cools enough to condense. Our condensate drain guide covers the code rule and compares the neutralizer and pump options in detail.
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When non-condensing still makes sense
Non-condensing isn’t obsolete. It wins when a unit mounts close to an existing masonry chimney or a short run of metal vent that’s already in place — there’s no new stainless to buy, and the lower unit price stands on its own. It’s also a reasonable pick for a simple outdoor-mounted install, where venting cost mostly disappears for either type and the non-condensing unit’s lower sticker price is the deciding factor. Outside of those two cases, a new indoor install with any real vent run tends to favor condensing.
Which should you buy?
- New indoor install with a vent run of 10+ feet: Buy condensing. The PVC-vs-stainless gap alone usually pays for the higher unit price. See our best gas tankless water heater picks.
- Unit sits right beside an existing short metal vent or chimney: Non-condensing can be the cheaper total install — check our Rheem lineup guide for the Performance Plus non-condensing option.
- Mounting outdoors: Venting cost mostly washes out either way; pick on unit price and features.
- Still deciding between electric and gas first? Read our electric vs gas comparison.
- Want the full installed-cost picture, not just the unit? See our 2026 tankless water heater cost guide and our venting guide for vent-material rules by fuel type.
The bottom line
For most new gas tankless installs, condensing wins: a 0.93–0.97 UEF versus 0.81–0.82, and PVC venting that typically saves $400–$800 over the stainless steel a non-condensing unit needs — savings that usually outrun the higher unit price on their own. Non-condensing only pulls ahead when the install sits beside a short existing metal vent or goes outdoors, where the venting-cost gap mostly disappears and the lower sticker price wins outright. Price your specific vent run before you decide — it matters more than the number on the box. Once you’ve picked a type, our tankless water heater sizing guide will get you to the right BTU and GPM.