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Here we discuss the basic components of solar hot water heating systems used to heat water for washing and bathing. Sketch at page top courtesy of Lennox Industries.

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How to Hook Up & Use Solar Water Heating Systems to Provide Domestic Hot Water

What are the Components of a Solar Hot Water Heating System?

The schematic at above left (U.S. Department of Energy) explains a typical active, closed loop solar water heater hookup and shows the basic parts of a solar hot water system. The schematic at above right (U.S. DOE) explains a typical passive-batch solar water heating system, showing the batch collector containing a volume of hot water and located separately from a backup solar water storage or water heater tank.

Here are the key parts of solar hot water heating:

• One or more solar collectors are located where they will receive an appropriate (or maximum) amount of sunlight. In our photo below you can see a simple solar collector hanging at the Don Pedro Ferreteria hardware store in San Miguel de Allende, Mexico.
• Heat exchanger: The solar hot water collectors are connected by a loop of piping to a heat exchanger unit located inside of a hot water storage tank located in the building. In other words, the building's domestic water supply to be heated is not itself circulated through the solar collector but rather it is heated inside the water tank by a heat exchanger which itself contains a liquid (containing an anti-freeze in northern climates) which circulates in the solar collectors and inside the heat exchanger.
• A hot water storage tank contains domestic hot water heated by the heat exchanger; the tank is supplied with incoming cold water and provides outgoing hot water to the building's plumbing fixtures. In our photo below you can see a simple solar water heater tank at the Don Pedro Ferreteria hardware store in San Miguel de Allende, Mexico. In areas where there is plenty of sunlight and water usage is more modest, a simple collector, pump, controls, and small water tank such as the one we show below are often adequate.

Temperature sensors mounted at the water storage tank and also at the solar collectors monitor water temperatures and communicate with a solar controller module. The solar controller module determines when it is appropriate to circulate water from the hot water tank through the solar collectors, preventing water circulation when it would cool rather than warm the hot water. A circulator pump is controlled by the solar controller module to move water between the solar collectors and the hot water storage tank. See Guide to Heating System Circulator Pumps & Circulator Relays for details. An expansion tank absorbs the pressure increase created in the (closed) system when water is heated. See Guide to Heating Boiler Expansion Tanks for details. A pressure and temperature relief valve is provided on the hot water tank for safety An air vent valve is provided at the solar collectors to avoid the piping becoming air bound, purging un-wanted air in the water circulation loop. A tempering valve or mixing valve is installed to mix cold water in with the outgoing hot water from the hot water tank, permitting storage of more heat in the water tank without risking scalding building occupants. We discuss tempering valves or mixing valves in detail at Guide to Mixing Valves & Anti Scald Valves A backup hot water heater is usually provided, using electricity, gas, oil, or other fuel to assure that there is adequate hot water when weather conditions do not provide enough solar energy.

As energy costs continue to increase the payback-time for the cost of solar panels and piping installation for solar hot water systems will continue to improve. The solar water heater system sketch is courtesy of Accu-Spect.

Especially in areas that receive adequate sunlight we should expect to see an increase in popularity of these systems.

A Comparison of Alternative Hot Water Heaters & Sources

Here we describe the characteristics of these water heating methods:

  High Efficiency Water Heaters such as direct-vent gas-fired water heaters
  Indirect-fired Water Heaters which use a separate heating boiler to produce a larger quantity of hot water
  Instantaneous Water Heaters point of use systems that have little or no standby energy losses
  Multiple water heaters in parallel to increase total hot water quantity
  Multiple water heaters in series to stage hot water heating for varying levels of demand
  Range Boiler Water Heaters an older form of indired-fired hot water heating used with separate heating boilers
  Side Arm Coil Water Heaters similar to instantaneous and tankless coil water heaters, often used with range boilers
  Solar Water Heaters using solar collectors, an indoor water tank, pump and controls, using minimal "on-grid" energy
  Tankless Coil for Hot Water a heat exchanging coil immersed inside of a heating boiler heats provides (somewhat limited) hot water, various tricks can significantly improve the safety and water quantity available

The characteristics of various water heaters such as life expectancy, cost, safety, and capacity are discussed at WATER HEATER PROPERTIES

Ways to improve hot water quantity, pressure, and flow are discussed beginning at HOT WATER IMPROVEMENTS and continuing at HOT WATER QUANTITY IMPROVEMENT.

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Technical Reviewers & References

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• Additional technical contributors & reference sources for this article are listed below.

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

• Additional technical contributors & reference sources for this article are listed below.
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
• Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
• Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
• The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the InspectAPedia Bookstore
• "Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
• "Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
  • "Heat Exchangers for Solar Water Heating Systems", U.S. DOE describes the types of solar water heater heat exchange methods between the sun and the building's hot water supply
  • "Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
  • "Solar Water Heating System Maintenance and Repair", U.S. DOE
  • "Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
  • "Scaling and Corrosion in Solar Water Heating Systems", U.S. DOE
  • www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 is the base U.S. DOE website for these articles
• "Active Solar Heating Systems", U.S. Department of Energy, including
  • "Radiant Heating Systems" U.S. DOE
  • "Absorption Heat Pumps & Coolers", U.S. DOE
  • "Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
  • "Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy inthe form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

More Information on Building Diagnostic Inspections and Repairs

• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• Dust from HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
• Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
• Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
• Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
• National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
• The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
• Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
• The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
• Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
• "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
• Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
• Installation Guide for Residential Hydronic Heating Systems
• Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
• The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)

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