Takagi T-K4-IN-NG Non-Condensing Tankless Water Heater

The Takagi T-K4-IN-NG is a non-condensing 190,000 BTU natural gas tankless water heater designed for medium-to-large residential installs. Takagi (a Japanese manufacturer acquired by Rheem in 2009) makes some of the most reliable mid-tier tankless heaters in the US market — the T-K4 has been in continuous production with iterative updates since 2004 and the field reliability data is strong.

Specs: 190,000 BTU input (natural gas; LP variants available), UEF 0.81 (non-condensing), 8.0 GPM at a 35°F rise or 4.0 GPM at a 70°F rise, copper heat exchanger with stainless steel exhaust, 4-inch Category III stainless steel B-vent (indoor model) or sealed direct-vent (outdoor model). 10-year warranty on the heat exchanger, 5-year on parts.

The T-K4 is positioned between Takagi's value tankless (T-H3 series, smaller BTU class) and their premium condensing line (T-H3J and T-H4J condensing units). For a household needing 199K BTU-class capacity without the install premium that PVC condensing venting carries, the T-K4-IN-NG offers a meaningful cost savings versus the Rinnai RU199iN or Navien NPE-240A. The tradeoff is the lower UEF (0.81 vs 0.96 condensing) and the requirement for stainless B-vent rather than PVC.

Right buyer: a household replacing an existing atmospheric gas tank that used a 4-inch B-vent chimney, where reusing the chimney for the tankless saves $800–$1,500 in venting work versus a condensing-tankless retrofit. The operating-cost penalty of UEF 0.81 vs 0.96 is roughly $50–$80/year for a typical household — meaningful but recovers slowly relative to the venting savings.

Now somewhat overshadowed in the Rheem catalog by the RTGH-95DVLN (Rheem's badged version of the equivalent Takagi platform), the T-K4-IN-NG is still sold through Takagi-direct channels at slightly lower pricing. About $1,200 unit, $2,800 installed.