Solar Water Heater Savings Calculator
Estimates annual energy savings from a solar water heater based on household size, fuel type, solar fraction. Use it when comparing solar thermal to conventional water heating costs.
Last updated: May 2026
Annual Savings
668.14 $
167.04: $140-220/person is typical when replacing electric resistance heating (2.8 factor), the most expensive fuel to offset and the fastest payback.
This is annual water-heating savings per person; per-capita savings depend heavily on displaced fuel, since electric resistance heating costs far more than gas to offset.
About this calculator
Solar water heaters displace conventional fuel use by pre-heating water with roof-mounted collectors. The calculator estimates annual energy displaced using: Energy Saved (kWh) = (householdSize × 15 gal/person/day × 365 days × 8.33 lb/gal × 50°F rise × 0.000293 kWh/BTU × solarFraction) / systemEfficiencyFactor. The 15-gallon-per-person-per-day figure is a standard US household average. The 50°F temperature rise assumes cold inlet water at ~60°F heated to ~110°F. The solar fraction (0–1) is the proportion of water heating load met by the solar system, typically 0.5–0.8 depending on climate. The fuel-type divisor converts raw BTU displacement into actual fuel units: natural gas systems have an efficiency of ~1.05 (high-efficiency), electric at ~2.8 (heat pump equivalent), and propane at ~1.5. The result is annual kWh-equivalent savings.
How to use
For a household of 4 people using electric water heating, a solar fraction of 0.7, with the standard constants: Step 1 — base energy: 4 × 15 × 365 × 8.33 × 50 × 0.000293 = 4 × 15 × 365 × 8.33 × 50 × 0.000293 ≈ 3,202 kWh. Step 2 — apply solar fraction: 3,202 × 0.7 = 2,241 kWh equivalent. Step 3 — divide by electric factor: 2,241 / 2.8 ≈ 800 kWh saved per year. At $0.13/kWh, that is roughly $104 in annual savings.
Frequently asked questions
How much money can I save annually with a solar water heater?
Annual savings vary widely based on household size, local fuel costs, and how much of your hot water load the solar system covers. A typical US family of 4 switching from electric resistance heating can save $200–$500 per year. Households using propane — which is expensive — often see even larger savings. Most solar water heaters pay back their installation cost in 5–10 years and carry warranties of 10+ years, making them a sound long-term investment in sunny climates.
What is solar fraction and how does it affect water heating savings?
Solar fraction is the percentage of your annual water heating energy demand supplied by the solar thermal system, expressed as a decimal between 0 and 1. A solar fraction of 0.7 means 70% of your hot water energy comes from the sun. Higher solar fractions require larger collector areas or better-insulated storage tanks. In sunny climates like the US Southwest, solar fractions of 0.75–0.85 are achievable; in cloudy northern climates, 0.40–0.60 is more typical. The solar fraction is the most important single input in the savings calculation.
Is a solar water heater worth it compared to a heat pump water heater?
Both technologies dramatically reduce water heating energy costs compared to conventional electric resistance heaters. Heat pump water heaters (HPWHs) are simpler to install, work in any climate, and achieve effective efficiency of 250–350%. Solar thermal systems have lower operating costs because they use free sunlight, but require roof space, collectors, and more complex plumbing. In very sunny climates, solar thermal can outperform HPWHs on a per-kWh-saved basis; in cloudy or cold climates, HPWHs are often the better choice. A combined solar-plus-heat-pump backup system offers the best of both.