Gas tankless · high draw
A. O. Smith ATO-240H 1
A. O. Smith ATO-240H 1 is a gas tankless water heater certified as a single rating set, 26 model numbers sold under six brand names, listed by A.O. Smith. Max flow 4.7 gal/min at a 67 °F rise from 160,000 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 ATO-240H 126 model numbers | 160,000 | 4.7 | 98% | 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 ATO-240H 1: max flow against gas input
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 | 4.7 gal/min | 5.2 gal/min | 12th lowest of 40, five 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 | 160,000 Btu/h | 180,000 Btu/h | 12th lowest of 40, five tied | 40 gas tankless sets |
Model numbers
The set covers 26 model numbers under six brand names, all certified 2023-02-23. An asterisk stands for a variant character in the model number.
| Model number | Brand | Vent | Fuel | Min flow | Certified |
|---|---|---|---|---|---|
| ATO-240H 1** | A. O. Smith | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| ATO-240H 1*1 | A. O. Smith | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| ATO-240HX3-N 1** | A. O. Smith | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| ATO-240HX3-P 1*1 | A. O. Smith | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| GT15-240-NO 1** | A. O. Smith | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT15-240-PO 1*1 | A. O. Smith | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| GT-240-NEH 1** | American | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT-240-PEH 1*1 | American | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| GT-240X3-NEH 1** | American | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GT-240X3-PEH 1*1 | American | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| LTO-240H-N 1** | Lochinvar | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| LTO-240H-P 1*1 | Lochinvar | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| LTO-240X3-N 1** | Lochinvar | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| LTO-240X3-P 1*1 | Lochinvar | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| TS-240-GEH 1** | Reliance | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TS-240-LEH 1*1 | Reliance | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| TS-240X3-GEH 1** | Reliance | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TS-240X3-LEH 1*1 | Reliance | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| GTS-240-NEH 1** | State | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GTS-240-PEH 1*1 | State | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| GTS-240X3-NEH 1** | State | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| GTS-240X3-PEH 1*1 | State | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| T-H3J-OS-N 1** | Takagi | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| T-H3J-OS-P 1*1 | Takagi | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
| TK-240X3-NEH 1** | Takagi | Power Vent | natural gas | 1.00 gal/min | 2023-02-23 |
| TK-240X3-PEH 1*1 | Takagi | Power Vent | propane | 1.00 gal/min | 2023-02-23 |
Nearest certified alternatives
| Rating set | Max flow | UEF | Gas input |
|---|---|---|---|
| Vesta VRP-PLUS-150 | ±0.0 gal/min | ±0.00 | −10,000 Btu/h |
| A. O. Smith ATHR-160M 1 | +0.1 gal/min | ±0.00 | same Btu/h |
| Bosch T9800 SE 160 | −0.1 gal/min | ±0.00 | same Btu/h |
| Noritz NRCR92DV (GQ-C2660WXQ-FF US) | +0.2 gal/min | ±0.00 | +5,000 Btu/h |