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Water Heater BTU Sizing Reference Values

Estimate required water-heater input in BTU/h from target flow rate and temperature rise.

Author

Dr. Ahmed Hassan

Plumbing editorial contributor

Egyptian structural engineer trained at Cairo University and MIT, specializing in earthquake-resistant building design

Reviewed for accuracy by

Prof. Zara Khan

Plumbing content reviewer

Pakistani-British education researcher at Cambridge, evaluating digital literacy programs in South Asian rural schools

Last updatedFebruary 22, 2026

PublishedFebruary 22, 2026

On this page

  1. All value pages
  2. Reference table
  3. FAQs
  4. Methodology and review
  5. Related conversions

Reference Value Index

This page lists 48 reference values for quick browsing and lookup.

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All Reference Values

Reference Table

Water Heater BTU Sizing reference values
Demand ScenarioHeater InputkW Equivalent
1 gpm at 30°F rise15,000 BTU/h4.4
1 gpm at 40°F rise20,000 BTU/h5.86
1 gpm at 50°F rise25,000 BTU/h7.33
1 gpm at 60°F rise30,000 BTU/h8.79
1 gpm at 70°F rise35,000 BTU/h10.26
1 gpm at 80°F rise40,000 BTU/h11.72
1.5 gpm at 30°F rise22,500 BTU/h6.59
1.5 gpm at 40°F rise30,000 BTU/h8.79
1.5 gpm at 50°F rise37,500 BTU/h10.99
1.5 gpm at 60°F rise45,000 BTU/h13.19
1.5 gpm at 70°F rise52,500 BTU/h15.39
1.5 gpm at 80°F rise60,000 BTU/h17.58
2 gpm at 30°F rise30,000 BTU/h8.79
2 gpm at 40°F rise40,000 BTU/h11.72
2 gpm at 50°F rise50,000 BTU/h14.65
2 gpm at 60°F rise60,000 BTU/h17.58
2 gpm at 70°F rise70,000 BTU/h20.51
2 gpm at 80°F rise80,000 BTU/h23.45
2.5 gpm at 30°F rise37,500 BTU/h10.99
2.5 gpm at 40°F rise50,000 BTU/h14.65
2.5 gpm at 50°F rise62,500 BTU/h18.32
2.5 gpm at 60°F rise75,000 BTU/h21.98
2.5 gpm at 70°F rise87,500 BTU/h25.64
2.5 gpm at 80°F rise100,000 BTU/h29.31
3 gpm at 30°F rise45,000 BTU/h13.19
3 gpm at 40°F rise60,000 BTU/h17.58
3 gpm at 50°F rise75,000 BTU/h21.98
3 gpm at 60°F rise90,000 BTU/h26.38
3 gpm at 70°F rise105,000 BTU/h30.77
3 gpm at 80°F rise120,000 BTU/h35.17
4 gpm at 30°F rise60,000 BTU/h17.58
4 gpm at 40°F rise80,000 BTU/h23.45
4 gpm at 50°F rise100,000 BTU/h29.31
4 gpm at 60°F rise120,000 BTU/h35.17
4 gpm at 70°F rise140,000 BTU/h41.03
4 gpm at 80°F rise160,000 BTU/h46.89
5 gpm at 30°F rise75,000 BTU/h21.98
5 gpm at 40°F rise100,000 BTU/h29.31
5 gpm at 50°F rise125,000 BTU/h36.63
5 gpm at 60°F rise150,000 BTU/h43.96
5 gpm at 70°F rise175,000 BTU/h51.29
5 gpm at 80°F rise200,000 BTU/h58.61
6 gpm at 30°F rise90,000 BTU/h26.38
6 gpm at 40°F rise120,000 BTU/h35.17
6 gpm at 50°F rise150,000 BTU/h43.96
6 gpm at 60°F rise180,000 BTU/h52.75
6 gpm at 70°F rise210,000 BTU/h61.54
6 gpm at 80°F rise240,000 BTU/h70.34

Frequently Asked Questions

Frequently asked questions for Water Heater BTU Sizing and its reference values.

How do you calculate water-heater BTU/h requirement?

A common estimate is BTU/h = 500 × flow (gpm) × temperature rise (°F).

Why include heater efficiency?

Input capacity must be higher than delivered heat when efficiency is below 100%, so efficiency adjusts required BTU/h input.

What is temperature rise in this context?

Temperature rise is the difference between desired outlet water temperature and incoming cold-water temperature.

Is this enough for final equipment selection?

Use this for preliminary sizing; final selection should also consider peak demand profile, recovery, storage, and manufacturer data.

Methodology and Review

Each row on this page links to a value detail page derived from the same conversion data file as the main calculator and reference table. This reduces inconsistencies across page variants.

Editorial metadata and structured data are rendered across the converter page and linked value pages. Review policies are documented in our review process and editorial policy.