Creating a Passive Hot Water System


Whether you realize it or not, you have experienced solar water heating. Have you ever turned on a water hose that had been spread out in your lawn and found the water to be very warm? This is one example. I'm sure you have also had a container of water sitting outdoors in the sun and found that it quickly heated up. These are both examples of passive solar water heating at work. The trick is to harness this water heating to use in your home to replace some or all of your electric or gas water heating requirements.

The most basic passive solar water heating system is not that much more complex than the container of water sitting outdoors and heating in the sun. A passive solar water heating system has no moving parts, no pollution, uses no fuel and is simply a water tank inside an insulated box with glazing to concentrate the heat placed in a southern –facing location so that the water can heat most efficiently.

To create a simple passive water heating system, you'll need a glass-lined water storage tank about 40 gallons in size. You can use a tank of almost any size you can find as long as it is not larger than 40 gallons. The easiest way to obtain a water storage tank is to find an ordinary water heater that no longer works. Strip the water heater of the outside shell and all the insulation, leaving the simple glass-lined water storage tank. You'll want to paint your water tank flat black using high temperature paint. Ask for engine paint or barbeque paint at your local hardware store.

Next you will need a solar collector box that is well insulated to hold in the heat of the sun. You'll want to use fiberglass insulation that comes in sheets and is commonly called batt insulation. If you live in a cold climate, you'll want to use more insulation than if you live in a mild climate.

Create your solar collection box of 2X4 lumber. After you build your solar collection box, you can cover exposed outside areas with siding that blends with your house or you can paint the exterior of the box.

You will want to base the size of your solar collection box on how large a water storage tank you selected but also to ensure that it is large enough to allow enough water heating to occur. A general "rule of thumb" to use is one square foot of top surface on the solar collection box for each 2 gallons of water you want to heat.

You will need double paned glass to create the top of your solar collection box. If you happen to be using a 40 gallon water tank, you can use a standard size sliding glass patio door for your collection box top. You can find other double paned glass to recycle into your solar collection box top if you prefer. The measurements of your glass for the collector top must be known before you build your box.

Based on the size of your glass and the tank you are using, build a box large enough to hold the tank inside that has top dimension that are the size of the double glazed glass. Position the tank inside the box with the inlet for cold water on the bottom and the outlet for hot water on the top. Insulate your water tank very well so that the heat will not be lost.

If you implement this simple design, keep in mind that a tank of water is heavy. If you use a 40 gallon tank, when full it will weight about 350 pounds. Plus you have the weight of your solar collector box to consider. These systems can only be used on structures that are very sound. Obviously this system can't be used on an old metal roof or on a mobile home. However, you can design a similar system that sits on the ground if you have a space that receives sufficient sunlight between 9 a.m. and 4 p.m.

You'll want to position this water heating system as close to the indoor water heater as possible. This will eliminate the loss of heat as the heated water passes through the plumbing.

You will, upon completion, connect plumbing from the cold water system to fill the tank and connect the heated water outlet to the water supply that fills your indoor water tank. If the solar heated water entering your hot water tank indoors is not hot enough, the thermostat in your home water heater will not turn on. In times of high demand or no sunshine, your ordinary home water heater will meet your needs for hot water.

The savings over only a few years can be significant with this very simple passive solar water heating system. Even if you must use some traditionally heated water, you'll still save a bundle!

About the Author: Anita van Wyk strives to make make more people aware of the benefits of using solar energy through her website

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