DOE sizes an instantaneous (tankless) water heater differently from a storage tank: Maximum GPM must be >= the summed flow rate of the hot water fixtures used at one time, tested at a 50°F household inlet unless you know your own. DOE's own worked example: a faucet (0.75 GPM) plus a shower head (2.5 GPM) run together needs 3.25 GPM — add up whichever fixtures you actually run at once for your own number.
What this registry's tankless models actually file, by DOE's own box
| Simultaneous-use box | GPM range (DOE) | Models on file | Real GPM spread |
|---|---|---|---|
| Very small | 0–1.7 GPM | 273 | 0.2–1.6 GPM |
| Low | 1.7–2.8 GPM | 10 | 1.8–2.5 GPM |
| Medium | 2.8–4 GPM | 81 | 2.9–3.9 GPM |
| High | 4–+ GPM | 399 | 4–8.5 GPM |
Tankless models on file, highest flow rate first
- Ranein RH19K-LPG : 8.5 GPM max — 206 therms/yr
- Ranein RH19K-NG : 8.5 GPM max — 206 therms/yr
- Vancepic VH19K-LPG : 8.5 GPM max — 206 therms/yr
- Vancepic VH19K-NG : 8.5 GPM max — 206 therms/yr
- Ranein RE27K : 6.5 GPM max — 5,334 kWh/yr
- A. O. SMITH ATM-199M-N 1** : 6 GPM max — 178 therms/yr
- AMERICAN ATM-199M-N 1** : 6 GPM max — 178 therms/yr
- GSW WATER HEATERS ATM-199M-N 1** : 6 GPM max — 178 therms/yr
- LOCHINVAR ATM-199M-N 1** : 6 GPM max — 178 therms/yr
- RELIANCE WATER HEATERS ATM-199M-N 1** : 6 GPM max — 178 therms/yr
- Rheem RTGH-RH11DVLN * : 6 GPM max — 180 therms/yr
- Richmond RTGH-RH11DVLN * : 6 GPM max — 180 therms/yr
Enter your own simultaneous-use total and every other constraint (fuel, footprint, ambient temperature) on the water heater selector to narrow this list further.
What it would cost installed in your state
Limits
A storage-tank model files a First Hour Rating, not a max GPM — it never appears in the table above, and this page does not size one. Estimating which fixtures actually run at the same time in your own household is the reader's own job; DOE's worked example is a starting point, not a measurement of your home.