Gas tankless · high draw
A. O. Smith ATHR-xxM 1
The A. O. Smith ATHR-xxM 1 line holds three certified rating sets of gas tankless water heaters, 62 model numbers sold under five brand names, listed by A.O. Smith. Gas input runs from 160,000 to 199,000 Btu/h, and max flow at a 67 °F rise runs from 4.8 to 5.9 gal/min. A. O. Smith ATHR-199M 1 lists 5.9 gal/min, the third highest of the 40 gas tankless sets (shared by two sets). A. O. Smith ATHR-160M 1, the set with the most model numbers, rates 0.01 below the median UEF 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
Size by size
| Rating set | Gas input, Btu/h | Max flow, gal/min | Share of heat ceiling | UEF | UEF rank | Therms/yr |
|---|---|---|---|---|---|---|
| A. O. Smith ATHR-160M 138 model numbers | 160,000 | 4.8 | 101% | 0.95 high | lowest of 39, 19 tied | 178 |
| A. O. Smith ATHR-180M 112 model numbers | 180,000 | 5.3 | 99% | 0.95 high | lowest of 39, 19 tied | 178 |
| A. O. Smith ATHR-199M 112 model numbers | 199,000 | 5.9 | 99% | 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 ATHR-xxM 1: max flow against gas input
A. O. Smith ATHR-xxM 1Other gas tankless sets
Max flow at a 67 °F rise, gal/min
Across the sizes
Moving from 160,000 Btu/h to 199,000 Btu/h of gas input lifts max flow from 4.8 gal/min to 5.9 gal/min, about 0.28 gal/min for each extra 10,000 Btu/h.
Strongest placings, size by size
| Measure | Value | Median of the group | Placing | Compared with |
|---|---|---|---|---|
| UEFA. O. Smith ATHR-160M 1 | 0.95 | 0.96 | lowest of 39, 19 tied | 39 high-draw gas tankless sets |
| Rated gas useA. O. Smith ATHR-160M 1 | 178 therms/yr | 176 therms/yr | highest of 39, 15 tied | 39 high-draw gas tankless sets |
| UEFA. O. Smith ATHR-180M 1 | 0.95 | 0.96 | lowest of 39, 19 tied | 39 high-draw gas tankless sets |
| Rated gas useA. O. Smith ATHR-180M 1 | 178 therms/yr | 176 therms/yr | highest of 39, 15 tied | 39 high-draw gas tankless sets |
| UEFA. O. Smith ATHR-199M 1 | 0.95 | 0.96 | lowest of 39, 19 tied | 39 high-draw gas tankless sets |
| Gas inputA. O. Smith ATHR-199M 1 | 199,000 Btu/h | 180,000 Btu/h | highest of 40, 13 tied | 40 gas tankless sets |
Model numbers
The line covers 62 model numbers under five brand names, first certified 2023-12-18 and most recently 2026-07-15. An asterisk stands for a variant character in the model number.
| Model number | Brand | Rating set | Vent | Fuel | Min flow | Certified |
|---|---|---|---|---|---|---|
| ATHR-160M 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| ATHR-160X3 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| ATM-160M-N 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| ATM-160M-P 1*1 | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| ATM-160X3-N 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| ATM-160X3-P 1*1 | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| GT15THR-160M 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15THR-160X3 1** | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15TM-160M-N | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| GT15TM-160M-N 1** | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | natural gas | 1.00 gal/min | 2026-07-15 |
| GT15TM-160M-P 1*1 | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| GT15TM-160X3-N | A. O. Smith | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| GT15TM-160X3-N 1** | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | natural gas | 1.00 gal/min | 2026-07-15 |
| GT15TM-160X3-P 1*1 | A. O. Smith | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| MTHR-160M 1** | American | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTHR-160X3 1** | American | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTM-160M-N 1** | American | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| MTM-160M-P 1*1 | American | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| MTM-160X3-N 1** | American | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| MTM-160X3-P 1*1 | American | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| LTHR-160M 1** | Lochinvar | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTHR-160X3 1** | Lochinvar | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTM-160M-N 1** | Lochinvar | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| LTM-160M-P 1*1 | Lochinvar | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| LTM-160X3-N 1** | Lochinvar | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| LTM-160X3-P 1*1 | Lochinvar | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| RTHR-160M 1** | Reliance | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTHR-160X3 1** | Reliance | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTM-160M-N 1** | Reliance | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| RTM-160M-P 1*1 | Reliance | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| RTM-160X3-N 1** | Reliance | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| RTM-160X3-P 1*1 | Reliance | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| STHR-160M 1** | State | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STHR-160X3 1** | State | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STM-160M-N 1** | State | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| STM-160M-P 1*1 | State | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| STM-160X3-N 1** | State | ATHR-160M 1 | Power Vent,Power Direct Vent | natural gas | 1.00 gal/min | 2025-04-21 |
| STM-160X3-P 1*1 | State | ATHR-160M 1 | Power Direct Vent,Power Vent | propane | 1.00 gal/min | 2026-07-15 |
| ATHR-180M 1** | A. O. Smith | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| ATHR-180X3 1** | A. O. Smith | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15THR-180M 1** | A. O. Smith | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15THR-180X3 1** | A. O. Smith | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTHR-180M 1** | American | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTHR-180X3 1** | American | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTHR-180M 1** | Lochinvar | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTHR-180X3 1** | Lochinvar | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTHR-180M 1** | Reliance | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTHR-180X3 1** | Reliance | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STHR-180M 1** | State | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STHR-180X3 1** | State | ATHR-180M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| ATHR-199M 1** | A. O. Smith | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| ATHR-199X3 1** | A. O. Smith | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15THR-199M 1** | A. O. Smith | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| GT15THR-199X3 1** | A. O. Smith | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTHR-199M 1** | American | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| MTHR-199X3 1** | American | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTHR-199M 1** | Lochinvar | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| LTHR-199X3 1** | Lochinvar | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTHR-199M 1** | Reliance | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| RTHR-199X3 1** | Reliance | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STHR-199M 1** | State | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
| STHR-199X3 1** | State | ATHR-199M 1 | Power Vent,Power Direct Vent | natural gas or propane | 1.00 gal/min | 2023-12-18 |
Nearest certified alternatives
| Rating set | Max flow | UEF | Gas input |
|---|---|---|---|
| A. O. Smith ATO-240H 1compared with A. O. Smith ATHR-160M 1 | −0.1 gal/min | ±0.00 | same Btu/h |
| Vesta VRP-PLUS-150compared with A. O. Smith ATHR-160M 1 | −0.1 gal/min | ±0.00 | −10,000 Btu/h |
| Noritz NRCR92DV (GQ-C2660WXQ-FF US)compared with A. O. Smith ATHR-160M 1 | +0.1 gal/min | ±0.00 | +5,000 Btu/h |
| Bosch T9800 SE 160compared with A. O. Smith ATHR-160M 1 | −0.2 gal/min | ±0.00 | same Btu/h |
| Midea JSG48-29PCH-LPcompared with A. O. Smith ATHR-180M 1 | −0.1 gal/min | ±0.00 | same Btu/h |