Best whole-house indoor gas tankless water heaters

Top pick: Rheem RTGH-95DVLN-3 — a condensing indoor natural-gas unit rated 9.5 GPM at 199,900 BTU/h with a 0.93 UEF. That flow covers two showers plus a dishwasher or laundry at once, and condensing venting is the easiest to route through an existing wall.

Who the others suit:

• Rheem IKONIC RTGH-S11i — the biggest flow here (11.2 GPM); pick it for a large household with simultaneous demand.
• Rheem RTG-84DVLN-3 — non-condensing, simpler and cheaper to vent; fine for a smaller home.
• Rheem RTGH-68DVLN-3 — condensing efficiency for a modest whole-house load.
• Takagi TK-110U-I — budget-friendly, ultra-low NOx, non-condensing.

Skip the 4–5 GPM ThermoMate and Camplux units: those are point-of-use, not whole-house.