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Free solar water heater savings calculator. Model annual backup fuel and electricity cost when a solar thermal system supplies part of your hot-water load, using the same load and efficiency framework as storage water heating tools. Explore more in our energy and sustainability calculator category.
Last updated: April 18, 2026
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Typical installed systems often fall in a wide range; use SRCC ratings or contractor estimates when possible.
Billed at your electricity rate below.
Conventional only
$266
231 therms/yr
With solar + pump
$128
Fuel $120 + pump $8
Estimated annual savings
$138
≈ 52% of modeled conventional cost.
Planning note
Resource
Fraction up
More annual solar yield increases modeled fuel displacement when matched to storage size.
Fuel
Therms avoided
Savings scale with displaced gas when solar fraction is meaningful.
kWh/yr
Net savings
High-flow pumps or long run hours reduce net savings versus a lean pumping package.
Load
Absolute $ up
Higher hot-water use increases both baseline cost and potential dollar savings at the same fraction.
Baseline
Lower fuel
A very efficient conventional system lowers the savings gap solar must bridge.
Ratings
Solar fraction
Use certified performance estimates for your city when available instead of guesses.
Default gas backup scenario: modeled annual savings about $138 vs conventional-only operation (after pump electricity).
Useful hot-water energy per year follows the common sensible heat estimate from daily gallons, 365 days, water density and specific heat expressed as BTU per gallon-degree, and temperature rise. Conventional annual fuel use applies storage UEF and a standby multiplier. The solar thermal system is represented by the fraction of that annual load not requiring backup fuel. Backup fuel scales linearly with the remaining fraction. Circulation and control electricity is priced separately at your utility rate.
Useful BTU/yr ≈ gpd × 365 × 8.34 × ΔTBackup fuel ≈ conventional fuel × (1 − solar fraction)With solar $ ≈ backup fuel $ + pump kWh × $/kWhAdjust solar fraction to match SRCC or contractor estimates for your location.
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