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

Water Heater Buying Guide - Residential Tankless Gas Water Heaters

GSW Residential Tankless Gas Water Heaters

GSW powered by Takagi offers tankless products to match the needs of today's average household.

State-of-the-art residential tankless water heaters, that include a condensing model, are all ENERGY STAR® qualified and provide an Energy Factor (EF) up to 0.95.

GSW powered by Takagi is your solution for endless hot water.


  • ENERGY STAR® qualified
  • Technology to meet today's demands
  • Growing demands throughout the home require a consistent, never-ending supply of hot water
  • Energy Savings
    • Plenty of hot water delivered in the most energy efficient way possible
    • Up to 0.95 Energy Factor
  • Eco-conscious
    • Use less energy: 20-50% energy savings compared to standard water heater
    • Efficient use of hot water
  • Serviceability
    • Condensing models have built-in display for easy diagnostics and troubleshooting
  • Limited 15-Year Residential Heat Exchanger Warranty
GSWT-540H Condensing Model

GSWT-540H Condensing Model Shown

Energy Star SA Certified

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


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 or 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-DV Specs

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

GSWT-540H-DV Specs

Product Features

  • ENERGY STAR® qualified
  • Power Vent design
  • Safety Features: Air-Fuel Ratio (AFR) Sensor, Exhaust & Water Temperature Safety Devices, Overheat Cutoff Fuse
  • Fully modulating
  • TK-RE02 temperature remote included
  • Factory-installed power cord
  • Vents with Cat.III stainless steel
  • Built-in freeze protection
GSWT-540H-DV 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 9.5
45 6.9 8.4
50 6.2 7.6
55 5.7 6.9
60 5.2 6.3
65 4.8 5.8
70 4.4 5.4
75 4.1 5.0
80 3.9 4.7
85 3.7 4.4
90 3.5 4.2
95 3.3 4.0
100 3.1 3.8
105 n/a 3.7
110 n/a 3.4
115 n/a 3.2
120 n/a 3.1

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.

Match the unit to your needs

Number of showers each GSW powered by Takagi unit can handle, depending on inlet water temperature.

40°F Incoming Groundwater Temperature

Model Capacity Number of Shower Heads
GSWT-310 2 Showers Showerhead Showerhead
GSWT-540H-DV 2 Showers Showerhead Showerhead

Assuming the outgoing temperature is 120°F.

Assuming a standard shower head of max 2.5 GPM.

Accessories Chart

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

Accessories Chart
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