When you consider a solar water heater, the upfront cost is only part of the picture. Understanding how efficiency is rated, what drives long-term savings, and how to compare proposals will help you make an informed decision. Solar water heating (solar thermal) uses collectors to capture the sun’s heat, not photovoltaic panels that generate electricity. This guide explains the key factors that influence solar water heater cost and performance, so you can evaluate a contractor’s bid with confidence.
How Solar Water Heater Efficiency Is Measured
Efficiency ratings let you compare how much hot water a system will deliver for the energy it consumes. ENERGY STAR defines the Solar Uniform Energy Factor (SUEF) as the energy delivered by the total system divided by the electrical or gas energy put into the system. To earn the ENERGY STAR label, a solar water heater must meet minimum SUEF thresholds, which differ for systems with electric backup and those with gas backup. The Solar Rating and Certification Corporation (SRCC) also provides independent performance ratings. According to the U.S. Department of Energy’s 2003 consumer guide, asking for bids on SRCC-certified systems helps ensure you are comparing equipment on a consistent basis. For a deeper look at these metrics, see our Efficiency Factors page.
What Determines Your Potential Savings
Several factors influence how much a solar water heater can reduce your energy bills. The North Carolina Solar Center points to hot water use, the backup fuel type, system size and type, and collector location. The DOE’s 2003 guide adds the climate, the contractor and the system rating. ENERGY STAR states that an ENERGY STAR certified solar water heating system can cut your annual hot water costs in half. However, the DOE guide cautions that when natural gas prices are very low, a solar water heater with a gas backup may cost more to own than a gas-only water heater. The same guide says that, depending on the price of the conventional fuel, a solar water heater can be more economical over the life of the system than heating water with electricity, fuel oil, propane or even natural gas. To see how different configurations stack up, visit our System Comparisons page.
Key Cost Factors in a Solar Water Heating System
The final price of a solar water heating installation includes more than the collectors and storage tank. The DOE guide recommends that a bid should cover installation labor, hardware, permits, sales tax, and warranties. Installation complexity varies: roof-mounted systems involve roof work and well-sealed roof penetrations, while ground-mounted systems need unshaded land and their own mounting. The type of freeze protection also affects cost. ENERGY STAR advises that in climates where temperatures may fall below 42°F, you should choose a closed-loop system with antifreeze or a drainback system, so the freeze protection approach is part of what you are paying for. Maintenance costs over the system’s life depend on the technology and local conditions. The DOE guide notes that simple passive systems need little upkeep, while active systems with pumps and controllers may require a replacement part after about 10 years. ENERGY STAR suggests periodic checks: keeping the collector clean and unshaded, inspecting seals and piping, and in hard-water areas, running a vinegar solution through the collector loop every three to five years to remove mineral buildup. For more on what drives installation and upkeep costs, see our Cost Factors page.
Comparing Solar Water Heaters with Conventional Models
When you look at water heater efficiency labels, you will see two different metrics. Conventional storage or tankless water heaters use the Uniform Energy Factor (UEF). Solar water heaters use the Solar Uniform Energy Factor (SUEF), which accounts for the solar energy contribution. ENERGY STAR explains that SUEF is the energy delivered by the total system divided by the electrical or gas energy put into the system. Because a solar water heater is designed to work alongside a backup heater, its overall efficiency includes both the solar fraction and the backup’s performance. This makes direct comparisons between a solar system and a standalone gas or electric unit more complex. A solar system typically preheats water, reducing the work the backup heater must do. To understand how backup heating integrates with solar, read our Backup Heating guide.
How to Evaluate a Solar Water Heater Proposal
Getting multiple bids is essential, but the lowest price is not always the best deal. The DOE guide advises that all bids should be based on the same information: system type and size, expected energy output, maintenance requirements, and a full breakdown of costs. The guide warns that a low price could be a sign of inexperience, or of a company without staying power. Ask each bidder to specify the system’s SRCC rating or ENERGY STAR certification so you can compare performance fairly. The table below lists key questions to ask and why each matters.
| Question for the proposal | Why it matters |
|---|---|
| What is the system type and size? | Different types (active, passive, drainback, glycol) suit different climates and freeze risks. Size should match your household’s hot water use; the North Carolina Solar Center suggests 10 to 18 square feet of collector area per person as a rough starting point. |
| What is the expected annual energy output? | This lets you compare the solar contribution across bids. Ask how it was estimated for your site, including orientation, tilt and shading. |
| What is included in the installation cost? | The DOE guide says cost should include installing the system and getting it running, plus hardware, permits, sales tax and warranties. Missing items can lead to surprise expenses later. |
| What warranties are provided? | A written installation warranty (for example, a 2-year parts-and-labor warranty) and manufacturer warranties on collectors, tanks, and other components protect you if something fails. Make sure you know what is covered and for how long. |
| What maintenance is required and at what cost? | Active systems need periodic checks of pumps, controllers, and freeze protection. In hard-water areas, de-scaling may be needed every few years. Knowing the expected upkeep helps you plan for the full cost of ownership. |
Once you have comparable bids, verify that the contractor is licensed and experienced. The DOE guide suggests asking for references and checking with your state contractor licensing board. ENERGY STAR recommends using a contractor certified by the North American Board of Certified Energy Practitioners (NABCEP) if possible. Also, remember that incentives can change. The North Carolina Solar Center points to DSIRE (dsireusa.org) as a resource for current federal and state incentives. Always confirm eligibility and amounts with official sources before signing a contract.
Frequently asked questions
How do I know if my roof is suitable for solar collectors?
ENERGY STAR advises that the roof should receive direct sunlight between 10 AM and 4 PM year round, face south (within 30 degrees of true south), and be sturdy with shingles in good condition. If the roof is not suitable, a ground-mounted system on unshaded land may be an alternative. For a detailed assessment, see our Roof and Site Suitability guide.
Does a solar water heater work on cloudy days?
The system preheats water whenever sunlight is available. On cloudy days or during high demand, the backup heater (electric or gas) takes over to bring the water to the desired temperature. The North Carolina Solar Center notes that cost-effective systems are sized to provide 50% to 80% of annual hot water needs, not 100%, because a system large enough to provide all of a home’s hot water must have enough collectors and storage to carry the household through several cloudy winter days in a row. Learn more about how sunlight and weather affect performance on our Climate and Sunlight page.
What maintenance does a solar water heater need?
Maintenance tasks include keeping the collector clean and free of shade, checking that seals and glazing are not cracked, and ensuring piping insulation is intact. In areas with hard water, you may need to run a de-scaling solution through the collector loop every three to five years. ENERGY STAR recommends an annual inspection by a qualified contractor. For a full checklist, visit our Routine Maintenance page.
For a broader look at costs, efficiency, and system comparisons, visit our Costs and Efficiency section.
