Section 9

Tankless flow and rise ratings compared with burner and element input

This table compares the rated flow and rise of 22 tankless models with the heat available from the burner or element. GPM times rise times about 500 is the BTU per hour going into the water. That number cannot be higher than the input.

9.1 Results by model

9.2 Notes on the percentages

• EcoSmart's table is at 96 to 99 percent of input, and Stiebel Eltron's DHC-E table is at 99 to 100 percent. Stiebel Eltron's Tempra flow table is about 2 percent above the calculated limit^[1]. The likely cause is a slightly different water density or unit factor in Stiebel Eltron's sheet. The difference is within rounding for sizing, and the Tempra ratings are used as listed.
• The Rinnai V53De table works out to 81 percent, close to its 0.81 UEF^[2]. The V65e and V75e are at 73 and 75 percent. Those are low because the curve points were estimated on the low side^[3][4].
• The Eccotemp SH12-A-LP is at 88 percent and the SH22 models are at 85 percent^[5][6]. Both are above the 73 to 81 percent of the Rinnai units.
• The Eccotemp SHLX-LP is at 98.5 percent from an 80,000 BTU burner^[7]. The rated flow and the burner input on Eccotemp's page do not fit together. The rating is shown as not confirmed and is not used in the sizer until Eccotemp lists a rise chart or a corrected input.

9.3 Use of the result

A rating that passes the heat balance is physically possible. A rating that does not pass needs a corrected number from the manufacturer.