Gas tankless · high draw
A. O. Smith ATI-340H 1
A. O. Smith ATI-340H 1 is a gas tankless water heater certified as a single rating set, 40 model numbers sold under six brand names, listed by A.O. Smith. Max flow 5.4 gal/min at a 67 °F rise from 180,000 Btu/h of gas input, UEF 0.95 at the high draw pattern. That UEF is 0.01 below the median of the 39 high-draw gas tankless sets (0.96).
Certified as of October 27, 2026 · EPA ENERGY STAR data, public domain · Compare in the Heater finder
Certified values
| Rating set | Gas input, Btu/h | Max flow, gal/min | Share of heat ceiling | UEF | UEF rank | Therms/yr |
|---|---|---|---|---|---|---|
| A. O. Smith ATI-340H 140 model numbers | 180,000 | 5.4 | 101% | 0.95 high | lowest of 39, 19 tied | 178 |
Share of heat ceiling: listed flow ÷ the flow the gas input could heat through 67 °F at 100% efficiency; test tolerances allow a little over 100%.
A. O. Smith ATI-340H 1: max flow against gas input
A. O. Smith ATI-340H 1Other gas tankless sets
Max flow at a 67 °F rise, gal/min
Where this set stands
| Measure | Value | Median of the group | Placing | Compared with |
|---|---|---|---|---|
| Max flow at a 67 °F rise | 5.4 gal/min | 5.2 gal/min | 14th highest of 40, two tied | 40 gas tankless sets |
| UEF | 0.95 | 0.96 | lowest of 39, 19 tied | 39 high-draw gas tankless sets |
| Rated gas use | 178 therms/yr | 176 therms/yr | highest of 39, 15 tied | 39 high-draw gas tankless sets |
| Gas input | 180,000 Btu/h | 180,000 Btu/h | 14th highest of 40, nine tied | 40 gas tankless sets |
Model numbers
The set covers 40 model numbers under six brand names, first certified 2023-02-23 and most recently 2026-05-27. An asterisk stands for a variant character in the model number.
| Model number | Brand | Vent | Fuel | Min flow | Certified |
|---|---|---|---|---|---|
| ATI-340H 1** | A. O. Smith | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| ATI-340H 1*1 | A. O. Smith | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| ATI-340HX3-N 1** | A. O. Smith | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| ATI-340HX3-P 1*1 | A. O. Smith | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| ATM-180M-N 1** | A. O. Smith | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| ATM-180X3-N 1** | A. O. Smith | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| GT15-340-NI 1** | A. O. Smith | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT15-340-PI 1*1 | A. O. Smith | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| GT15TM-180M-N | A. O. Smith | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| GT15TM-180M-N 1** | A. O. Smith | Power Direct Vent,Power Vent | natural gas | 1.00 gal/min | 2026-05-27 |
| GT15TM-180X3-N | A. O. Smith | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| GT15TM-180X3-N 1** | A. O. Smith | Power Direct Vent,Power Vent | natural gas | 1.00 gal/min | 2026-05-27 |
| GT-340-NIH 1** | American | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT-340-PIH 1*1 | American | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| GT-340X3-NIH 1** | American | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT-340X3-PIH 1*1 | American | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| MTM-180M-N 1** | American | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| MTM-180X3-N 1** | American | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| LTI-340H-N 1** | Lochinvar | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| LTI-340H-P 1*1 | Lochinvar | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| LTI-340X3-N 1** | Lochinvar | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| LTI-340X3-P 1*1 | Lochinvar | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| LTM-180M-N 1** | Lochinvar | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| LTM-180X3-N 1** | Lochinvar | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| RTM-180M-N 1** | Reliance | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| RTM-180X3-N 1** | Reliance | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| TS-340-GIH 1** | Reliance | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TS-340-LIH 1*1 | Reliance | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| TS-340X3-GIH 1** | Reliance | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TS-340X3-LIH 1*1 | Reliance | Power Direct Vent | propane | 1.00 gal/min | 2023-07-12 |
| GTS-340-NIH 1** | State | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GTS-340-PIH 1*1 | State | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| GTS-340X3-NIH 1** | State | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GTS-340X3-PIH 1*1 | State | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| STM-180M-N 1** | State | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| STM-180X3-N 1** | State | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| T-H3S-DV-N 1** | Takagi | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| T-H3S-DV-P 1*1 | Takagi | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
| TK-340X3-NIH 1** | Takagi | Power Direct Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TK-340X3-PIH 1*1 | Takagi | Power Direct Vent | propane | 1.00 gal/min | 2023-02-23 |
Nearest certified alternatives
| Rating set | Max flow | UEF | Gas input |
|---|---|---|---|
| Bosch T9800 SE 199 | ±0.0 gal/min | ±0.00 | +19,000 Btu/h |
| A. O. Smith ATHR-180M 1 | −0.1 gal/min | ±0.00 | same Btu/h |
| Navien NPE-240A2 | +0.2 gal/min | ±0.00 | +19,000 Btu/h |
| Midea JSG48-29PCH-LP | −0.2 gal/min | ±0.00 | same Btu/h |