Tankless Size Chart

Flow rate and temperature rise of small tankless water heaters for ADUs, cabins and off-grid buildings

Section 2

Tankless water heater GPM at 30 to 80 F temperature rise

These tables list the flow rate of 22 small tankless water heaters at 30, 40, 50, 60, 70 and 80 F temperature rise. Flow falls as the rise goes up. Rise is the outlet temperature minus the ground water temperature.

A 105 F shower with 37 F water is a 68 F rise. With 62 F water it is a 43 F rise. A 120 F set point with 42 F water is a 78 F rise.

Table 2.1 Electric whole-house models, GPM at each rise. Sources: notes 1 and 2.
ManufacturerModel30 F40 F50 F60 F70 F80 FRated points
Stiebel EltronTempra 12 Trend / Plus2.82.11.71.41.21.0Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
Stiebel EltronTempra 15 Trend / Plus3.32.52.01.71.41.2Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
Stiebel EltronTempra 20 Trend / Plus4.43.32.72.21.91.7Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
Stiebel EltronTempra 24 Trend / Plus5.54.23.32.82.42.1Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
Stiebel EltronTempra 29 Trend / Plus6.65.04.03.32.92.5Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
Stiebel EltronTempra 36 Trend / Plus6.66.25.04.23.63.1Stiebel Eltron flow table, 105 F outlet at 240 V, inlet 39, 59 and 77 F
EcoSmartECO 81.71.31.00.90.80.7EcoSmart zone table, 105 F set point, ground water 37 to 77 F
EcoSmartECO 112.92.21.71.41.21.1EcoSmart zone table, 105 F set point, ground water 37 to 77 F
EcoSmartECO 184.03.02.42.01.71.5EcoSmart zone table, 105 F set point, ground water 37 to 77 F
EcoSmartECO 245.44.13.22.72.32.0EcoSmart zone table, 105 F set point, ground water 37 to 77 F
EcoSmartECO 276.14.63.63.02.62.3EcoSmart zone table, 105 F set point, ground water 37 to 77 F
EcoSmartECO 368.16.14.94.13.53.0EcoSmart zone table, 105 F set point, ground water 37 to 77 F
Table 2.2 Point-of-use electric models, GPM at each rise. Source: Stiebel Eltron DHC-E Classic technical specifications.
ManufacturerModel30 F40 F50 F60 F70 F80 FRated points
Stiebel EltronDHC-E 8/10 Classic (set to 9.6 kW)1.51.51.31.10.90.8Stiebel Eltron table of maximum rise at 0.75, 1.0 and 1.5 GPM, 240 V
Stiebel EltronDHC-E 8/10 Classic (set to 7.2 kW)1.51.21.00.80.70.6Stiebel Eltron table of maximum rise at 0.75, 1.0 and 1.5 GPM, 240 V
Stiebel EltronDHC-E 12 Classic2.72.01.61.41.21.0Stiebel Eltron table of maximum rise at 1.0 to 3.0 GPM, 240 V
Table 2.3 Propane wall-mounted models, GPM at each rise. Sources: notes 3 to 6.
ManufacturerModel30 F40 F50 F60 F70 F80 FRated points
RinnaiV53DeP (propane) / V53DeN5.34.93.93.22.82.4Rinnai ground water table, 120 F set point, ground water 35 to 77 F
RinnaiV65eP (propane) / V65eN6.55.54.43.73.12.8Estimated from Rinnai's water flow curve, to about plus or minus 0.15 GPM
RinnaiV75eP (propane) / V75eN7.56.85.44.53.93.4Estimated from Rinnai's water flow curve, to about plus or minus 0.15 GPM
EccotempSmartHome SH12-A-LP (indoor)4.03.52.82.32.01.8Eccotemp product page, 4.0 GPM at 35 F rise, 80,000 BTU
EccotempSmartHome SHLX-LP (indoor)Not confirmedNot confirmedNot confirmedNot confirmedNot confirmedNot confirmedEccotemp product page, 4.5 GPM at 35 F rise, 80,000 BTU
EccotempSmartHome SH22-LP (outdoor)6.86.04.84.03.43.0Eccotemp product page, 6.8 GPM at 35 F rise, 140,000 BTU
EccotempSmartHome SH22-ILP (indoor)6.86.04.84.03.43.0Eccotemp product page, 6.8 GPM at 35 F rise, 140,000 BTU

2.4 Notes on the tables

  • Stiebel Eltron Tempra flows come from Stiebel Eltron's flow table at 240 V[1]. The same table lists lower flows at 208 V, so these rows cover 240 V only.
  • EcoSmart flows come from the zone table in EcoSmart's sizing sheet, which rounds to 0.1 GPM[2]. Rounding makes the smallest product slightly low, so the flows listed here are slightly low.
  • Rinnai V53De flows come from Rinnai's printed table[3]. V65e and V75e flows are estimated from Rinnai's water flow curves[4][5], to about plus or minus 0.15 GPM.
  • Eccotemp lists a single point for each SmartHome model, GPM at a 35 F rise[6]. Flows at other rises assume the same heat output, as in the formula on the home page.
  • Rows marked "Not confirmed" did not pass the heat balance in section 9.

Notes and sources

  1. Stiebel Eltron, Tempra table of flow rates at temperature rises (technical bulletin PDF)
  2. EcoSmart, electric tankless sizing sheet with zone table, 105 F set point (PDF)
  3. Rinnai, non-condensing tankless brochure with United States Ground Water Temperature Map and V53De table, 06/2022 (PDF hosted by Woodstove Pro)
  4. Rinnai, V65e specification sheet with water flow curve (PDF)
  5. Rinnai, V75e specification sheet with water flow curve (PDF)
  6. Eccotemp, SmartHome SH12-A-LP product page
  7. Stiebel Eltron, DHC-E Classic technical specifications, rev. 6.2025 (PDF)