Radiant Heat Solar Installation Details

Solar panels are practical anywhere the sun shines. The main question becomes: How many panels will I need?

In the deserts of the American Southwest, and most southern regions of the country, three to five panels can provide enough hot water to supply up to 90% of all domestic hot water and space heating requirements. The northern tier states (like Vermont, for example) may require six or more panels. Sizing the proper number of collectors will always depend upon how well insulated your home is, how much area you plan to heat, and how much domestic hot water you use. With this information, the technicians at Radiant Floor Company will factor in all the variables and recommend the proper number of panels for your individual situation.

The following photos show a complete solar water heater installation in the high desert of Southeastern Arizona. It may surprise you, but the temperatures here commonly hit the teens during the winter months. The 5000 ft. elevation, the clear nights, and sparse vegetation invite a precipitous drop in temperature once the sun goes down. Snow falls several times a year in this location….and Mexico is less than 20 miles south!

Flat Plate Solar Hot Water Collectors

Flat Plate Solar Hot Water Collectors

The above panels provide more than 64 sq. ft. of collector area. The low iron tempered glass allows more than 91% transmissivity (which is basically an engineer’s way of saying that, unlike regular glass, more light hits the copper absorber plate and less is reflected). The panels are insulated with fiberglass and polyisocyanurate foam to R-12. Fluid enters the panels at the lower right hand corner and exits from the upper left.

Putting it All Together

A lot of different elements come together to make a successful solar heating system. You pay initially to bring those elements together, then every operating day the system pays back your investment. It’s a good feeling to know that, with every passing sunny day, the system costs you less and less. And when the break even point is reached, it’s reasonable to expect the system to continue to pay an energy dividend for many years to come.

When you look at the entire system, fully plumbed and wired, it may seem daunting at first. But after carefully studying the solar schematic and these photos, it will all make perfect sense. First, here’s a breakdown of the necessary elements:

  1. A way to collect and transfer the free solar heat to a storage/back-up tank (panels and circulator pumps)
  2. A way to prevent the heat transfer medium from freezing (anti-freeze and heat exchanger)
  3. A back-up system for guaranteed hot water on sunless days (propane/electric back-up storage tank)
  4. A method of tempering the extremely hot water that solar panels can produce (mixing valve)
  5. A design to prevent stagnation in the tubing when the heating system is off during the summer months (check valve)
  6. Sensors to trigger the pumps when heat is available, and shut them off when the storage tank is charged with hot water
  7. Pressure relief safety valves to protect the system
  8. Gauges to monitor the system’s performance
  9. A way to control the expansion and contraction caused by the daily heating and cooling of the anti-freeze (expansion tank)
  10. A method of filling and draining the system, as well as purging air on a continual basis (solar EPK/air eliminator)

Plumbing a Solar Heated Radiant System -(and you get domestic hot water too)

The first few photos show the plumbing in progressive increments, starting with the solar Expansion and Purge Kit (EPK).

This will make it easier to grasp the overall plumbing configuration and not get bogged down by the somewhat daunting appearance of the fully completed job. It really is easier than it may look…..especially when the solar schematic is used as a road map.

Solar Example 1The solar EPK is a factory pre-assembled and tested component. A Grundfos circulator pump is mounted into a set of flanges and the entire assembly is easily attached to the wall. Note the two vertical copper pipes. These are the supply and return lines from the soon to be heated radiant slab. The tank on the right is a Bradford/White 75 gallon propane fired water heater. During periods of limited or no sun, the water heater guarantees plenty of heat for both domestic and space heating needs.
Solar Example 2The next step in the plumbing process involves installing the heat exchanger (lower left). The connection on the upper left side of the heat exchanger will receive the heated anti-freeze from the solar panels (next photo). This fluid heats the exchanger, exits from the bottom left, flows up through the solar EPK, then returns to the panels to be re-heated. Notice that the domestic (potable) side of the heat exchanger has been plumbed to supply the top of the storage tank with hot water. I’m sure you can see that the next connection will be from the lower outlet of the storage tank to the lower right inlet port of the heat exchanger (see photo below).
Solar Example 3This photo shows the storage/back-up tank tied into the fully plumbed heat exchanger. The horizontal pipe directly below the heat exchanger is the cold supply into the system. Remember, this is an “open” radiant system. The storage tank supplies hot water to both the heated slab and the home’s domestic system. So, when hot water is removed from the tank for showers, dishes, etc., cold make-up water must enter the system to replace it. The next photo illustrates how this is done.
This elegant configuration of plumbing won the Southeastern Arizona Regional Plumbing as Performance Art Award.

This elegant configuration of plumbing won the Southeastern Arizona Regional Plumbing as Performance Art Award.

Well, okay, so we made up the award and gave it to ourselves (along with a beer to celebrate). But the fact remains, plumbing IS art and it certainly performs. I’ll try to give a basic tour of its more functional and artistic elements.

First off, notice how the hot water from the tank enters a three-way mixing valve. The connection opposite the hot is the cold return from the radiant floor. Note the tee fitting branching off from this same return line. It flows past the temperature and pressure gauge and enters the cold inlet of the storage tank. This plumbing detail enables the return water to both temper the scalding hot water from the solar heated tank and also replenish the storage tank with fresh water whenever hot is drawn off for domestic purposes. The “mix” outlet of the mixing valve (pointing straight up) sends the tempered water to the floor and to the house domestic system.

The last plumbing detail of note is the one way valve seen here coming off the tee connected to the “mix” line. Immediately after the one way valve you can see a branch of the house cold supply entering the system. The one way valve forces the cold water to flow left, through the circulator (the circulator is free flowing, allowing water to flow through it even when off), then down into the floor. Of course, the cold water can only enter the radiant system when hot water is removed from the tank for some domestic hot water purpose. When no hot faucets are open in the house, the radiant system is essentially “closed”. If the floor calls for heat, the circulator draws hot water from the tank, but it can’t pull cold water from the cold supply.

At this point you may be asking: Why is the cold make-up water to the water heater going through the floor first?

The answer is to prevent the water in the tubing from stagnating during the off season. Normally, when domestic hot water is used, a corresponding amount of fresh water enters the water heater to replace it. In an “open” radiant system, this fresh make-up water flows to the water heater via the floor. This keeps the water in the tubing fresh year-round.

For a more detailed explanation of why this makes perfect sense, see the open system page of this web site.

Controller and Sensorsresol controller

This controller activates the appropriate circulator pumps when heat is available and deactivates the same pumps when the tank is charged with hot water or when the sun goes down.



An inexpensive drill pump can be used to charge the system with anti-freeze. Follow the instructions outlined in our Design and Installation Manual or under Filling a Closed System with Anti-freeze section of this website.