Takagi install requirements are similar to other tankless brands. T-T commercial cascade adds the multi-unit complexity.
Gas line sizing
| Model | BTU | Min gas line |
|---|---|---|
| T-KJr2 (140k) | 140k | ½" to 30 ft / ¾" over 30 ft |
| T-H1 (120k) | 120k | ½" to 30 ft / ¾" over 30 ft |
| T-H3J (140k) | 140k | ¾" required |
| T-K4 (190k) | 190k | ¾" required |
| T-M50 (175k) | 175k | ¾" required |
| T-H3, T-D2 (199k) | 199k | ¾" required (1" over 50 ft) |
| T-T1, T-T2 (199k) | 199k | ¾" or 1" depending on length |
| T-T cascade (per unit) | see manifold sizing | 1¼" or 1½" common to manifold |
Venting
- Condensing (T-H3, T-D2, T-T condensing): 2" or 3" Schedule 40 PVC. Up to 100 ft equivalent length
- Non-condensing (T-K, T-KJr, T-H1): stainless Category III venting
- Outdoor variants: no venting required
Condensate drainage (condensing models)
- Trap at unit outlet (Takagi includes)
- PVC drain line to floor drain or condensate pump
- Neutralizer if discharging to iron pipe or septic
- Insulate or heat-trace drain through unconditioned spaces
Water softener
Required above 11 grains per gallon hardness for warranty.
T-T commercial cascade specifics
For cascade installs up to 6 units:
- Cascade controller (Takagi-supplied)
- Daisy-chain wiring between units
- Manifold piping (gas, water in/out, condensate)
- Isolation valves per unit
- Common-vent design
Use a Takagi/AO Smith-trained commercial installer.
Outdoor unit freeze protection
Outdoor variants (T-H3-OS, T-D2-OS, T-K4-OS, T-KJr2-OS) include freeze protection — but require 120V power to operate. In cold climates with potential multi-day power outages, install a battery backup or generator transfer switch for the heater circuit.
Commissioning
- Purge air from gas line
- Open isolation valves
- Power on; verify display
- Set temperature (120°F default)
- For condensing: verify condensate flowing
- Register warranty
Permits
Required in most US jurisdictions.
Bottom line
Standard Takagi installs are within range of competent plumbers. T-T cascade requires Takagi/AO Smith-trained commercial installer.