DIY Batch Water Heaters
Building Tips and Ideas

Check out the characteristics of batch water heaters and tips on how to build and install one? Find out the benefits of the most popular DIY passive solar water heaters. Explore ideas on how to use the old heater and utilize the free solar energy to heat water.

A batch water heater, also known as the Integral Collector Storage (ICS) and breadbox collector, is the simplest of all passive water heating systems. It is considered passive as it doesn't require a pump and controllers for its operation; it combines collection and storage and uses natural convection for water transfer.

Its advantage over other types is that it is easy and fast to design and make without using expensive materials.


The main benefits of the batch solar water heaters are free water heating and affordability. The system is easy to make at home and can be built for a few hundred dollars, some for even less, depending on are you using new or recycled components.

Who can make this type of a heater?

If you are a handyman, have the tools and some of the major components (tank, garden hose, insulation, plastic cover), the solar heater can be made in one day and almost for free.

The most economical way is to use the old water heater, actually, the storage tank, only if it is not leaking and is free of sediment deposits.

Basically, the success of building the batch water heater depends on several factors, but the main ones are the ability to collect and store sufficient solar energy.

These passive solar water heating systems are recommended for those who live in the south, in the sunny region with frost-free climates, and where water is not extremely hard.

Tips on how to make a batch water heater

Plan ahead

You can design your own batch water heater, which will suit your needs, or you can find one of many plans and designs online. Here are a few good ones: DIY projects, here and this guide in pdf, from Florida Solar Energy Center.

Increasing the absorbance

The simplest solar batch water heater design is the black-painted water tank installed in the box, properly insulated. For example, the 2"x4" wood frame and plywood for the exterior is the easy one. The wooden block will be used to support the tank.

The black paint is used as it is cheap and has high absorbance, so the reflection is minimal.

Installing the reflective surface under the tank (internal reflector in concave shape) and sides (external reflector) is beneficial to collect even more sun's heat. The best solutions for reflectors are aluminum foil, polished aluminum, or mirrored surfaces.

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Reducing the heat loss

Next, a good quality and thick insulation is significant as it can retain the heat longer when the temperature drops during the night. It is recommended to use the insulation with a high R-value, for example, R-20 in colder areas. The fiberglass insulation, hardboard, or aluminum-based foam are good enough to cover the interior.

The tank should be covered with plastic or tempered glass (glazing) since this is the primary reason for the heat loss. The former one is more expensive but lasts longer and is better at transmitting the heat.

The cover can have several layers of glazing and should be very transparent for the incoming sun's heat and reduce the outgoing heat or heat loss.

Another tip that reduces heat loss is to use silicone caulking and seal all the cracks and joints.

You can also install an external blanket on the top of the box cover and reduce the heat loss during the night.

Plumbing tips

The system is plumbed into the house water system, where the cold water flows to the bottom while the hot water flows out of the top of the tank.

Another essential part is the pressure and temperature relief valve, which releases the pressure if it increases above the allowed (factory set).

Location tips

The most popular tank sizes are 40 and 50-gallon capacities, and this is probably the tank size you will use for your DIY solar water heating project. If you plan to put the heater on the roof of your home, keep in mind that the unit full of water can weigh more than 500 pounds, which makes it hard to install and maybe too heavy for the roof.

This is why the best location is on the ground level, side by side with your home or garage.


  • The batch water heater should effectively collect solar energy and retain the heat for a long time.
  • The unit should be the right size and provide enough hot water.
  • The heater and the system should be durable with no leakage.
  • The heater should be installed in a sunny spot and have maximum exposure during the day (facing south).

Note: Professional installation and repair recommended.

The batch water heater is an inexpensive way of water heating, which might be used for a simple shower after swimming in the pool or used to feed the existing gas or electric water heater, therefore increasing the incoming water temperature heated and reducing the total costs.


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