Water Heater BTU Sizing
Estimate required water-heater input in BTU/h from target flow rate and temperature rise.
3 gpm at 30°F rise =
45,000 BTU/h
Representative value from the Water Heater BTU Sizing reference table.
Reference Values
Browse 48 reference values with individual detail pages for quick lookup.
Water Heater BTU Sizing Calculator
Estimate required heater input for a target hot-water flow and temperature rise.
Required Heater Input
—
Reference Table
Use this complete table for quick lookup and internal linking to specific value pages.
| Demand Scenario | Heater Input | kW Equivalent |
|---|---|---|
| 1 gpm at 30°F rise | 15,000 BTU/h | 4.4 |
| 1 gpm at 40°F rise | 20,000 BTU/h | 5.86 |
| 1 gpm at 50°F rise | 25,000 BTU/h | 7.33 |
| 1 gpm at 60°F rise | 30,000 BTU/h | 8.79 |
| 1 gpm at 70°F rise | 35,000 BTU/h | 10.26 |
| 1 gpm at 80°F rise | 40,000 BTU/h | 11.72 |
| 1.5 gpm at 30°F rise | 22,500 BTU/h | 6.59 |
| 1.5 gpm at 40°F rise | 30,000 BTU/h | 8.79 |
| 1.5 gpm at 50°F rise | 37,500 BTU/h | 10.99 |
| 1.5 gpm at 60°F rise | 45,000 BTU/h | 13.19 |
| 1.5 gpm at 70°F rise | 52,500 BTU/h | 15.39 |
| 1.5 gpm at 80°F rise | 60,000 BTU/h | 17.58 |
| 2 gpm at 30°F rise | 30,000 BTU/h | 8.79 |
| 2 gpm at 40°F rise | 40,000 BTU/h | 11.72 |
| 2 gpm at 50°F rise | 50,000 BTU/h | 14.65 |
| 2 gpm at 60°F rise | 60,000 BTU/h | 17.58 |
| 2 gpm at 70°F rise | 70,000 BTU/h | 20.51 |
| 2 gpm at 80°F rise | 80,000 BTU/h | 23.45 |
| 2.5 gpm at 30°F rise | 37,500 BTU/h | 10.99 |
| 2.5 gpm at 40°F rise | 50,000 BTU/h | 14.65 |
| 2.5 gpm at 50°F rise | 62,500 BTU/h | 18.32 |
| 2.5 gpm at 60°F rise | 75,000 BTU/h | 21.98 |
| 2.5 gpm at 70°F rise | 87,500 BTU/h | 25.64 |
| 2.5 gpm at 80°F rise | 100,000 BTU/h | 29.31 |
| 3 gpm at 30°F rise | 45,000 BTU/h | 13.19 |
| 3 gpm at 40°F rise | 60,000 BTU/h | 17.58 |
| 3 gpm at 50°F rise | 75,000 BTU/h | 21.98 |
| 3 gpm at 60°F rise | 90,000 BTU/h | 26.38 |
| 3 gpm at 70°F rise | 105,000 BTU/h | 30.77 |
| 3 gpm at 80°F rise | 120,000 BTU/h | 35.17 |
| 4 gpm at 30°F rise | 60,000 BTU/h | 17.58 |
| 4 gpm at 40°F rise | 80,000 BTU/h | 23.45 |
| 4 gpm at 50°F rise | 100,000 BTU/h | 29.31 |
| 4 gpm at 60°F rise | 120,000 BTU/h | 35.17 |
| 4 gpm at 70°F rise | 140,000 BTU/h | 41.03 |
| 4 gpm at 80°F rise | 160,000 BTU/h | 46.89 |
| 5 gpm at 30°F rise | 75,000 BTU/h | 21.98 |
| 5 gpm at 40°F rise | 100,000 BTU/h | 29.31 |
| 5 gpm at 50°F rise | 125,000 BTU/h | 36.63 |
| 5 gpm at 60°F rise | 150,000 BTU/h | 43.96 |
| 5 gpm at 70°F rise | 175,000 BTU/h | 51.29 |
| 5 gpm at 80°F rise | 200,000 BTU/h | 58.61 |
| 6 gpm at 30°F rise | 90,000 BTU/h | 26.38 |
| 6 gpm at 40°F rise | 120,000 BTU/h | 35.17 |
| 6 gpm at 50°F rise | 150,000 BTU/h | 43.96 |
| 6 gpm at 60°F rise | 180,000 BTU/h | 52.75 |
| 6 gpm at 70°F rise | 210,000 BTU/h | 61.54 |
| 6 gpm at 80°F rise | 240,000 BTU/h | 70.34 |
Frequently Asked Questions
Common questions about Water Heater BTU Sizing, formulas, and typical use cases.
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
This page combines a live calculator, precomputed reference values, and FAQ content from the same conversion definition to reduce mismatch between calculator output and lookup tables.
Editorial metadata (author, reviewer, and update date) is rendered on the page and in structured data. See our editorial policy, review process, and corrections policy.
For compliance-sensitive work, verify final values against project requirements, governing standards, and manufacturer documentation.