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Water Heater Recovery Time Calculator

Estimate how long a storage water heater takes to reheat a full tank after it's been drawn down.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax

Recovery time

58.39 minutes

Check your inputs

This estimates recovery from a fully-drained tank using nameplate BTU input — real-world recovery is somewhat slower due to standby losses and burner cycling.

Recovery rate
0.86 gal/min

For the dimensions entered, expect a recovery time of 58.4 minutes. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Standard recovery formula: recovery rate = (power input × 0.75 efficiency) ÷ (8.33 BTU/gal·°F × temperature rise); recovery time = tank capacity ÷ recovery rate. Metric inputs convert at the formula's boundary.

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Frequently asked questions

Why does colder incoming water slow recovery so much?
The heater has to raise the water temperature by a bigger margin (a larger 'temperature rise'), which takes proportionally more energy and time for the same BTU input — this is also why tankless units are rated lower GPM in cold climates.
Does a bigger tank always mean longer recovery?
For the same burner size, yes — more gallons take longer to reheat. That's why higher-capacity tanks are sometimes paired with a higher-BTU burner to keep recovery time reasonable.
How is this different from the first-hour rating on the yellow EnergyGuide label?
First-hour rating (FHR) combines usable stored hot water plus one hour of recovery, a single number for comparing models at point of purchase. This calculator estimates recovery time for a specific temperature rise and BTU input you provide, which is more precise for your actual conditions.