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Home > Projects & DIY Toolkit > Buying Guides > Water Heater Buying Guide - Tankless Gas Water Heaters

Water Heater Buying Guide - Tankless Gas Water Heaters

GSW Tankless Gas Water Heaters

GSW powered by Takagi offers a selection of tankless products to suit the varying needs of today's households.

The GSW line of state-of-the-art residential tankless water heaters, which includes a condensing model, are ENERGY STAR® qualified with a minimum 0.82 EF and offer great energy savings.


Energy Savings

  • ENERGY STAR® qualified
  • Fully modulating

Designed for Performance

  • Factory-installed power cord
  • Temperature remote included with GSWT-310 model
  • Many models feature improved scale reduction software
  • Secondary heat exchangers feature high-quality, long-lasting stainless steel components on condensing models
  • Eliminates the "cold water sandwich" Safety Features
  • Air-Fuel Ratio Sensor to ensure safe and optimal operation
  • Exhaust & water temperature safety devices
  • Overheat cut-off fuse
  • Freeze protection


  • Condensing models have built-in display for easy diagnostics and troubleshooting

The Ultimate in Venting Flexibility

  • Condensing models can be vented using ULC s636 PVC, CPVC or polypropylene pipe or Cat. III/IV stainless steel
GSWT-540H Condensing Model

GSWT-540H Condensing Model Shown

Energy Star SA Certified


12 Year Limited Tank Warranty

5 Year Limited Parts Warranty

Consult installation manual for terms and conditions or visit for more information.


GSWT-310 Light/Medium Residential, 4.4 GPM at 70°F temperature rise

GSWT-310 Chart

Product Features

  • ENERGY STAR® qualified
  • Power Vent design
  • Safety Features: Air-Fuel Ratio (AFR) Sensor, Exhaust & Water Temperature SafetyDevices, Overheat Cutoff Fuse
  • TK-RE02 temperature remote included
  • Factory-installed power cord
  • Vents with Cat.III stainless steel
  • Built-in freeze protection
GSWT-310 Specs

GSWT-540H Condensing, 5.5 GPM at 70°F Temperature Rise

GSWT-540H Chart

Product Features

  • Condensing technology
  • Unprecedented 0.95 Energy Factor
  • Durable Heat Exchanger: Uses HRS35 copper for primary heat exchanger and Stainless Steel #316L for secondary heat exchanger
  • Approved with ULC s636 PVC, CPVC or polypropylene venting in addition to Cat. IV Stainless Steel
  • Vent with 3" (up to 70 feet) or 4" (up to 100 feet)
  • 0" Clearance to combustibles
  • Integrated control and diagnostics
  • Air Fuel Ratio (AFR) Sensor
  • Factory-installed power cord
  • Dual internal freeze-protection system
GSWT-540H Specs

residential flow rate guide GUIDE

USG per minute

Temp Rise (°F) GSWT-310 GSWT-540H-DV
30 8.0 10.0
35 8.0 10.0
40 7.8 19.5
45 6.9 18.0
50 6.2 17.7
55 5.7 17.0
60 5.2 16.3
65 4.8 15.8
70 4.4 15.5
75 4.1 15.0
80 3.9 14.8
85 3.7 14.5
90 3.5 14.3
95 3.3 14.0
100 3.1 13.8
105 3.0 13.7
110 2.8 13.4
115 2.7 13.2
120 2.6 13.1

Flow rate is determined by temperature rise. To determine your temperature rise, subtract the incoming water temperature from the set output temperature. All units are factory set at 120°F to 122°F but can be changed. Flow rates are based on default set temperatures. In Canada, base incoming water temperature for coldest climate on 40°F.

Accessories Chart

Complement your GSW powered by Takagi tankless water heater with manufacturer recommended accessories.

Accessories Chart
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