Solar Water Heaters
Updated February 20, 2026
Eco-friendly systems that use solar panels to heat water. Great for sunny climates and long-term savings.
Overview
Solar water heaters use rooftop collectors to capture the sun energy and transfer it to your hot water supply. Two types: active (pumped) systems circulate fluid through the collectors, and passive (thermosiphon) systems rely on natural convection. Both use a storage tank and typically include a backup conventional heater for cloudy days and high-demand periods. Can reduce water heating costs by 50-80%% in sunny climates. High upfront cost, but long lifespan (20-30 years for collectors) and significant utility savings.
Key Features
- Rooftop solar collectors capture free thermal energy from the sun
- Active systems use a pump and controller; passive systems use natural convection
- Direct systems circulate potable water through collectors; indirect systems use antifreeze fluid with a heat exchanger
- Storage tank holds pre-heated water; backup heater boosts temperature when needed
- Can reduce water heating energy use by 50-80%% in sunny climates
Sizing & Selection
Rule of thumb: 20 square feet of collector area and a 50-80 gallon storage tank for a family of 2-4. Larger families or higher hot water demand need proportionally more collector area. South-facing roof with minimal shading is ideal. The backup heater (electric or gas) must be sized to handle full demand independently for extended cloudy periods.
Installation
Professional installation required. Collectors mount on the roof with structural attachments. Piping runs from collectors to the storage tank (insulated). Active systems need a pump, controller, and expansion tank. Indirect systems need a heat exchanger and food-grade antifreeze (propylene glycol). Permits and inspections are typical. Installation cost is ,000-7,000 depending on system size and complexity.
Maintenance
- Inspect collectors annually for damage, debris, and shading from tree growth.
- Check glycol antifreeze concentration and pH annually in indirect systems -- replace every 3-5 years.
- Flush the storage tank annually to remove sediment.
- Check the pump and controller in active systems annually. Listen for unusual noise or cycling patterns.
- Collectors last 20-30 years. Storage tanks and pumps may need replacement sooner (10-15 years).
Buying Tips
- Flat-plate collectors are the standard for residential. Evacuated tube collectors are more efficient in cold climates but cost more.
- Federal tax credit (30%% of total system cost) applies to solar water heaters. State incentives may add more.
- In cold climates (freeze risk), indirect (antifreeze) systems are required. Direct systems only work in freeze-free areas.
- Calculate payback period based on your local solar resource, current energy costs, and available incentives. Typical payback: 5-10 years.
- A solar water heater can pair with a heat pump water heater as the backup for maximum efficiency -- solar pre-heats, heat pump finishes.