Lesson 4
Installing Solar Water-Heating Systems


To say there are a lot of variables in installing solar water-heating systems would be an understatement. As you learned in Lesson 3, there are a number of different system types, and the components used will vary from manufacturer to manufacturer. Every home is a little different, and getting the plumbing from the collectors to the storage tank may require removal of plaster or sheet rock, which then must be replaced. You may be faced with building a pipe chase in which to run the piping.

In this lesson, we will focus on installing a basic closed-loop solar water-heating system. The links below will provide more insight into system installation. Before the actual solar system installation can take place, a site survey must be done to answer questions such as:

  • Can the roof support the dead load of the solar collectors and the live load of the installation crew?
  • Is the roof properly oriented with enough un-shaded area and surface that does not need to be replaced in the near future?
  • Can the roof work be done safely?
  • Is there room in the building for the storage tank and associated hardware?
  • Can the plumbing lines be installed between the storage tank and the collectors without a significant remodeling effort?

For a quick review of some of solar water-heating components and their relationship to each other, see Gly-Mod-WB-SND (used with permission from AAA Solar Supply, 2021 Zearing NW, Albuquerque, NM 87104). You will need Flash Player 5 or 6 plug-in to view the video.

If you have a Mac computer, go to AAA Solar Supply’s website at: www.aaasolar.com/video/#menu to download the Mac version.

AAA Solar Supply also granted permission to use its GlycolModule video, [Windows Media 16.4MB] which illustrates the components and assembly of an antifreeze solar water-heating system and how to sweat-solder copper pipes and fittings. You will need Windows Media Player to view the video. If you do not have Windows Media Player, you can view the video with Real Player or Quick Time Player at AAA Solar Supply’s website at: www.aaasolar.com/video/#menu.

The Florida Solar Energy Center (FSEC), University of Central Florida, 12443 Research Parkway, Orlando, FL 32826 and the Solar Rating and Certification Corporation (SRCC), c/o FSEC, 1679 Clearlake Road, Cocoa, FL 32922, have granted permission to use their materials on installing solar water-heating systems.

Section 3 from Solar Water and Pool Heating Manual – Design and Installation & Repair and Maintenance , produced by FSEC, covers the steps involved in installing a solar water-heating system without a separate solar storage tank. See also FSEC’s SDHW System Installation.pdf [internal link], which provides pictures to complement the Chapter 3 text file.

Unlike solar water-heating systems installed in Florida, systems installed in Pennsylvania will have to be freeze-protected. What this means is that the freeze-protected system will include a heat exchanger, a non-toxic heat transfer fluid, an expansion tank, and depending on the system installed, another circulation pump may be required.

AAA Solar Supply’s information on filling a glycol system [PDF /14KB] provides practical information that you will need to install systems in Pennsylvania.

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Installation Steps

The basic steps to install a closed-loop solar water-heating system are:

  1. Mount the solar collectors on the roof
  2. Install the solar storage tank and heat exchanger next to conventional water heater
  3. Install the piping and pump for the glycol loop
  4. Install the water piping
  5. Install the controls
  6. Fill the system
  7. Insulate the water and glycol lines
schematic illustrating the components of a solar water-heating system
This schematic illustrates components of a solar water-heating system.


Step 1: Mount the solar collectors on the roof

When mounting collectors, make as few roof penetrations as possible. In some cases, the collectors can be mounted on a roof and the piping run through a vertical wall instead of through the roof. Seal all roof penetrations with silicone sealant. Different manufacturers will supply slightly different hardware for mounting the collectors on the roof. Follow the manufacturer’s directions carefully.

Locate the rafters to which you will be attaching the collectors. You may be able to do this with a stud finder, or you may have to go inside the attic space and drill a small hole next to a rafter to locate it. Drill the hole, and then run a small wire out of the hole to help locate it on the outside. Remember to seal the hole with silicone sealant.

solar collector schematic

Rafters are usually 16 inches or 24 inches center to center. If you cannot attach the collector mounting hardware to the rafter itself, you must install a spanner block between the rafters and mount the collector hardware to the sleeper. Do not rely on the roof sheathing to support the solar collectors. Be sure that the collector mounting hardware is securely attached to the framing members.

mounting hardware schematic


rooftop pv panels

Use the manufacturer’s recommended flashing around piping going through the roof, or use pipe flashing. Install the flashing with roof sealant to be sure it will not leak.

roof and ground mounting prcedures

If you are using sweated copper plumbing fittings, protect the roof from the torch with a flame-resistant mat.

Remember to install an air vent at the top of the collector.

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Step 2: Install the storage tank and heat exchange next to the conventional water heater
Place the solar storage tank near the conventional water heater. If the heat exchanger is internal to the storage tank, make sure that the glycol loop connections to the heat exchanger and the cold and hot water connections are accessible. If the heat exchanger is external to the storage tank, it is likely that it is supported by the plumbing. Install unions at the storage tank and heat exchanger connections so that the piping will not have to be cut if the tank or heat exchanger ever need to be replaced.

insulated water heaters

Solar water-heating systems use both direct and diffuse solar radiation. Despite being a colder, northern climate, Pennsylvania still offers an adequate solar resource. Generally, if the installation site is un-shaded from 9 a.m. to 3 p.m. and faces south, it's a good candidate for a solar water-heating system.

glycol loop setup

Step 3: Install the piping and pump for the glycol loop

In most systems, the piping for the glycol loop is no bigger than ½-inch pipe. Assemble the entire glycol loop without solder so you can be sure the entire loop will go together, and then solder the entire loop. Be sure to install unions at the pump, so if it ever needs to be replaced, it can be replaced without cutting the piping.

The pump should be installed at the lowest part of the glycol loop. The pump outlet is plumbed to the piping leading to the solar collectors on the roof. A check valve must be installed at the outlet of the pump so that when the pump is turned off, the glycol will not flow backwards around the loop. An expansion tank must be installed, and a pressure gauge should be installed to monitor the pressure in the glycol loop. A pressure relief valve must be installed in the glycol loop. The outlet from the pressure relief valve should be piped to a drain. This pressure relief valve should be a boiler relief valve, and the operating pressure should be no more than 30 psi. Optional Equipment:

  • A ball valve or circuit setter may be installed to control the flow in the loop
  • A flow meter also may be installed in the glycol loop
  • Thermometers on the inlet and outlet of the heat exchanger will help to monitor system performance



glycol loop setup

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Step 4: Install the water piping
Plumb the cold water energy in the house to the inlet of the solar storage tank, and the outlet of the solar storage tank to the inlet of the conventional water heater. Install valves and unions on the inlets and outlets of the tanks. If the heat exchanger is external to the solar storage tank, you may choose to use a natural convection loop between the heat exchanger and the solar storage tank, or you may install a pump to force water through the heat exchanger and tank. If you choose to use natural convection, you should use a large pipe—at least 1-1/4" copper—to get adequate flow through the heat exchanger. If you choose to install a pump to force water through the heat exchanger, you can use ½-inch copper pipe.

Step 5: Install the controls
The differential controller must be installed to sense the temperature difference between the water at the bottom of the solar storage tank and the glycol at the top of the solar collectors. The sensors can be attached to the pipes with hose clamps.

differential controls

There are some optional additions to this part of the system that, while adding additional costs, will add convenience and possibly safety to the system. Optional equipment includes:

  • Bypass valve
  • Tempering valve
  • High-temperature radiator loop

Bypass valve: Run a pipe between the water pipe entering and the water pipe leaving the conventional water heater. Install a valve in this pipe (bypass valve). When this valve is closed and the valves on the inlet and outlet of the conventional water heater are open, water will flow from the solar storage tank to the conventional water heater (normal operation). If the valves on the water pipe entering and the water pipe leaving the conventional water heater are closed and the bypass valve is open, water will flow from the solar storage tank past the conventional water heater. This bypass mode can be used in the summertime when water temperatures are high, and the conventional water heater can be shut off completely.

Tempering valve: To avoid scalding temperatures from the solar storage tank, a tempering valve may be installed after the conventional water heater. The tempering valve adds cold water to the hot water to control the temperature so that there is no risk of scalding.

High-temperature radiator loop: A radiator, pump, and controls may be installed on the system to “dump” energy in case the glycol loop gets too hot. This addition to the system can protect the system from overheating if there is no hot water used for several days in the summertime.

high temperature radiator loop

An example of a heat rejection loop using a radiator.


  • The solar collector heats the solar storage tank through the bottom coil in the tank.
  • Heat rejection loop removes excessive heat when tank temperature (TT) exceeds its design limit.

Source: www.thermomax.com/Heat_Rejection.htm

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Step 6: Fill the system
Check the glycol loop for leaks by filling the glycol loop with water. The circulation pump will probably be too small to fill the system, so you will need a fill pump that can provide enough pressure to lift the water (and glycol) up to the top of the solar collectors. A drill pump has successfully been used to fill solar water-heating systems. To test the system for leaks, being sure that there is no air in the glycol loop, overpressure the glycol loop to twice the operating pressure (30 PSI maximum, and less than the pressure relief valve rating) and let the system stand for eight hours. If the pressure in the loop has dropped, you have a leak that must be found and repaired. If the pressure holds, fill the system with a 50-percent propylene glycol 50-percent water mixture and pressurize the loop to no more than 15 PSI.

fill system


fill system

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Step 7: Insulate water and glycol lines
After the system has been checked for leaks, carefully insulate all of the glycol and water lines. Water piping can be insulated with standard foam pipe insulation. Glycol piping and external heat exchangers should be insulated with fiberglass pipe insulation. Duct tape can be used on the joints of the water piping insulation, and use the joint tape that comes with fiberglass piping insulation. Insulation exposed to sunlight can be protected by a foil wrap, or UV resistant paint. Fiberglass insulation used outside should be protected with PVC insulation covers.

Appendix 6 from FSEC’s Solar Water and Pool Heating Manual (Appendix.pdf) provides an extensive list of tools needed to install, service, and repair solar water-heating systems.

The troubleshooting information presented in FSEC’s Solar Water and Pool Heating Manual [PDF/266KB] offers methods for diagnosing and correcting problems in solar water-heating system installations.

Two useful sources from SRCC that provide valuable information on installing a solar water-heating system are OG-300 Solar Water Heating Systems – Installation Guidelines and Training Video for Inspection of Solar Water Heating Systems (the Outdoor Inspection and Indoor Inspection segments within this video review system installation from the perspective of an inspector). You will need Quick Time 7 to view the segments. You can choose large, medium, or small format versions depending on your connection speed (use the smaller version for slower connection speeds). The transcripts of these segments are available by clicking on the following links:


  1. During the initial site survey, what are five important building characteristics to evaluate?

  2. What are the three common methods of installing the collector mounting clips?

  3. Where must the lag screw be when installing a mounting clip in a rafter and why?

  4. Why is a compression block needed when installing a mounting clip between rafters?

  5. For a one-story building, what is a method of getting the collectors on the roof and how many people are required to do so?

  6. Although not given in the materials presented in this lesson, how could you get solar collectors on the roof of a two- or more-story building?

  7. Why should you be careful when lifting shingles to make it possible to install a copper flashings for the plumbing lines?

  8. What function does the flashing cap perform?

  9. Why is it necessary to clean and flux both surfaces of copper pipes and fittings before sweat soldering?

  10. Why is it necessary to install the collector plumbing lines such that the collectors can be drained?

  11. What could be the result if you install a temperature/pressure relief valve near the collector outlet?

  12. Why does the automatic air vent valve have to be installed in a vertical position?

  13. Where are the proper places to install a differential controller’s sensors?

  14. What is main reason that soft copper piping is installed between the storage tank and the collector inlet and outlet?

  15. Why install a check valve in a solar water-heating system?

  16. In a freeze-protected solar water-heating system, how do you fill the system with the heat transfer fluid and when is it best to do the task?

  17. Why is an expansion tank needed in a freeze-protected solar water heating system?

  18. Why should a by-pass line and ball valves be installed between the solar storage tank and the conventional domestic hot water heater?

  19. Why is it important that you fill and pressurize the solar water heating system before installing insulation on the plumbing lines?

  20. After installing pipe insulation on the exterior plumbing lines, how do you protect the insulation from UV degradation?

  21. After turning the solar water heater "on" and giving the building owner a walk-through, what printed materials should be left at the building?

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