DIY Batch Water Heaters: Building Tips and Ideas

Batch water heaters offer an environmentally friendly and cost-effective solution for meeting household hot water needs.

Utilizing the abundant and renewable energy of the sun, these systems harness solar radiation to heat water, reducing reliance on conventional energy sources, such as gas and electricity, and cutting down utility costs.

In this guide, we'll explore the intricacies of building a batch-type solar water heater including benefits, from the initial planning stages to the final touches of installation.

This comprehensive approach is designed to equip homeowners, DIY enthusiasts, and renewable energy advocates with the knowledge and skills needed to construct their own solar water heating system, contributing to a greener, more sustainable future.

batch water heaterBatch water heater

Understanding batch water heaters

Batch water heaters, also known as Integral Collector Storage (ICS) and breadbox collectors, represent the simplest form of all passive water heating systems.

They are considered passive because they operate without the need for pumps or controllers. These systems comprise a sizable, well-insulated tank or collector that directly captures sunlight and utilizes it to heat water.

One of their notable advantages over other types of water heaters is their ease of design and construction, achieved without the use of expensive materials. This simplicity makes them a cost-effective choice for those looking to harness solar energy.

Perhaps the most significant benefit of batch water heaters is their capacity to reduce your dependence on conventional energy sources.

By doing so, they help diminish your carbon footprint and lead to substantial savings in utility costs.

Exploring the benefits

Batch water heaters are celebrated for their exceptional energy efficiency and cost-effectiveness. By harnessing the power of the sun, you can significantly diminish your reliance on non-renewable energy sources, leading to reduced energy bills and a notable decrease in greenhouse gas emissions.

What's more, these systems are remarkably straightforward to create at home, and they can be assembled for just a few hundred dollars, and even less if you opt for recycled components. The overall cost depends on whether you use new or repurposed materials.

Furthermore, once these systems are installed, they demand minimal maintenance, offering long-term reliability and providing peace of mind. This makes them an attractive choice for homeowners seeking a hassle-free solution.

These passive solar water heating systems are especially recommended for individuals residing in regions with abundant sunshine, frost-free climates, particularly in the southern areas.

They are most effective in areas with relatively soft water, as extremely hard water can potentially cause mineral buildup over time.

Things to consider when making your own batch water heater

Climate considerations

Before embarking on building a batch-type solar water heater, it's crucial to evaluate the solar resources available in your area. This involves understanding the intensity and duration of sunlight your location receives throughout the year.

Climate factors, such as the number of sunny days, the angle of the sun, and temperature variations, also play a significant role.

This assessment helps in determining the feasibility and design of your solar water heater to ensure it operates efficiently in your specific geographic and climatic conditions.

Determining hot water needs

The next step involves calculating the hot water demand for your household.

This depends on the number of occupants, typical water usage patterns, and peak hot water usage times. Estimating these factors accurately is essential for determining the size and capacity of the solar water heater you need to build.

An undersized system might not meet your hot water needs, while an oversized one could lead to unnecessary costs and inefficiency.

Choosing the location

Selecting the right location for your batch-type solar water heater is critical for optimal performance.

The ideal spot should have maximum exposure to sunlight, minimal shading from trees or buildings, and should align well with the sun's path.

Additionally, the location should be structurally sound to support the weight of the system, especially if it's installed on a roof, and should be easily accessible for maintenance and adjustments.

Gathering necessary tools and materials

It's advisable to source high-quality materials and appropriate tools to ensure the durability and efficiency of the system. This preparatory step ensures a smooth building process, minimizing delays and potential issues during construction.

  • Large, insulated tank or collector (typically 40-80 gallons)
  • Insulating material (fiberglass, foam board, or similar)
  • Black paint or solar absorber coating
  • Copper or PEX tubing
  • Valves and fittings
  • Pipes and hose
  • Temperature and pressure relief valve
  • Solar heat transfer fluid (propylene glycol or water)
  • Plywood or framing material
  • Screws, nails, and tools (saw, drill, screwdriver, etc.)
  • Insulation for pipes (foam or rubber)

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Design principles

Overview of key components

  • Water heater tank: The reused water heater tank serves as the core component, holding the water to be heated. It's coated with black heat-resistant paint or a solar absorber coating to maximize heat absorption.
  • Insulated box: An insulated box, constructed around the tank, provides protection and heat retention. It's slightly larger than the tank and lined with insulation materials to prevent heat loss.
  • Glazing: Glazing, typically made of transparent material such as glass or polycarbonate, is used to cover the top opening of the insulated box. It allows sunlight to enter the system while minimizing heat loss. The glazing acts as a protective barrier, ensuring that the collected solar energy is effectively retained within the system to heat the water in the tank. Properly sealed and well-maintained glazing is crucial for maximizing the system's efficiency and overall performance.
  • Plumbing connections: Copper or PEX tubing connects to the tank's inlet and outlet ports, creating a closed-loop system for water circulation. Valves and fittings control water flow.
  • Reflectors: Reflective materials, positioned inside the box as internal and external reflectors, concentrate sunlight onto the tank, enhancing heat absorption.
  • Temperature and pressure relief valve: Installed on the tank for safety, this valve prevents pressure buildup and temperature spikes within the system.
  • Solar heat transfer fluid: Propylene glycol or water is used as the heat transfer fluid within the system, filling the closed-loop to facilitate heat exchange.
  • Insulated pipes: Insulation on the pipes connected to the tank minimizes heat loss during hot water distribution throughout the household.
  • Secure mounting: Proper mounting and securing ensure the stability and longevity of the system, preventing movement or tipping.

Material selection

Choosing the right materials is critical for the efficiency and longevity of a batch-type solar water heater.

The collector's transparent cover (glazing) should be made of durable, high-transparency materials like tempered glass or clear polycarbonate to withstand environmental conditions while maximizing solar penetration.

Metals used in the collector and tank, such as copper or stainless steel, should have good thermal conductivity and resistance to corrosion.

Insulation is also key; materials like polyurethane foam or rock wool can effectively reduce heat loss, especially in colder climates.

Note that these material choices directly impact the system's thermal performance and durability.


The size and dimensions of a batch-type solar water heater should be tailored to meet the specific hot water demands of the household and the available solar resource.

The size of the tank is determined by daily water usage, ensuring enough hot water even on less sunny days.

The surface area of the solar collector is another critical dimension, which should be large enough to absorb sufficient solar energy to heat the water in the tank.

However, it should also be proportional to the tank volume to avoid overheating.

The dimensions of these components should also consider the installation space, ensuring the system fits well within the designated area while maintaining optimal exposure to sunlight.

How to build a batch water heater: Step-by-step instructions


Prepare the water heater tank

Begin by thoroughly cleaning the reused water heater tank to remove any residual sediment or debris. It's crucial to ensure the tank is in good working condition with no leaks or structural issues to ensure efficient operation.

Paint the tank in black

Apply a layer of black heat-resistant paint or a solar absorber coating to the exterior of the tank. This coating is essential for maximizing heat absorption from sunlight, which is a key factor in the system's efficiency. Allow the paint to dry completely according to the manufacturer's instructions before proceeding.

Build an insulated box

Construct an insulated box around the tank using plywood or framing materials. The box should be slightly larger than the tank, providing enough space for proper insulation. This box serves as the protective housing for the water heater components.

Install the cover (glazing)

Glazing, typically made of transparent material such as glass or polycarbonate, is used to cover the top opening of the insulated box.

It allows sunlight to enter the system while minimizing heat loss. The glazing acts as a protective barrier, ensuring that the collected solar energy is effectively retained within the system to heat the water in the tank.

Properly sealed and well-maintained glazing is crucial for maximizing the system's efficiency and overall performance.

Insulating the box

Line the interior of the box with insulating materials such as fiberglass or foam board. The insulation is vital for retaining the heat generated by the solar energy, preventing heat loss to the surroundings, and ensuring optimal performance of the system.

It is advisable to use insulation with a high R-value, such as R-20, especially in colder regions.

Mount the tank

Securely mount the black-painted water heater tank inside the insulated box. Proper positioning and attachment are essential to maintain stability and ensure that the tank receives maximum exposure to sunlight.

Create plumbing connections

Connect copper or PEX tubing to the tank's inlet and outlet ports to create a closed-loop system for water circulation. Install valves and fittings as necessary to control the flow of water through the system, allowing for efficient heat transfer.

Add reflectors

Enhance the system's efficiency by placing reflective materials on the interior surfaces of the box. Pay particular attention to positioning reflectors underneath the tank (internal reflector) and on the sides (external reflector). These reflectors will redirect and concentrate sunlight onto the tank, further increasing its heat absorption capacity.

The best solutions for reflectors are aluminum foil, polished aluminum, or mirrored surfaces.

Install a TPR valve

Install a temperature and pressure relief valve on the water heater tank to ensure safe operation. This valve serves as a crucial safety feature, preventing excessive pressure buildup and temperature spikes within the system.

Fill the system

Fill the batch solar water heater system with a suitable solar heat transfer fluid, such as propylene glycol or water. Carefully remove any air bubbles from the system to maintain efficient heat transfer.

Thoroughly check for any leaks during this process and address them promptly to prevent heat loss.

Insulate pipes

Insulate the pipes connected to the tank to minimize heat loss as the heated water is distributed throughout your household. Proper insulation will help maintain hot water temperatures and improve the overall energy efficiency of the system.

Position and secure

Select a sunny location with good sun exposure for your batch solar water heater installation. Properly secure the system in place to prevent any movement or tipping, ensuring its stability and effectiveness in harnessing solar energy.

Integration tips

It is recommended to incorporate a back-up heating solution for times when the solar water heater cannot meet the full hot water demand, such as during cloudy days or in the colder months.

This can be achieved by maintaining the existing conventional water heater (like an electric or gas heater) in the system.

Also, when integrating a batch-type solar water heater with an existing water heating system, you can choose between a parallel or series configuration.

In a parallel setup, the solar heater and the existing system operate independently, each connected to the plumbing network.

This allows for flexibility; if the solar heater provides sufficient hot water, the existing heater remains off, reducing energy consumption.

In a series configuration, the solar heater pre-heats the water before it enters the existing heater. This arrangement can be more efficient, as the existing heater only needs to raise the water temperature slightly if the solar heater has already heated it.

The choice between parallel and series depends on factors like climate, hot water demand, and the type of existing heater.

Here are some ideas with plans and designs found online: DIY projects on and in this guide in pdf, from Florida Solar Energy Center.

Long-term durability tips

To enhance the long-term durability of your batch water heater, consider a few tips.

  • Regularly check the condition of seals, gaskets, and insulation materials, as these can degrade over time.
  • Keep an eye on the tank's sacrificial anode rod and replace it when needed to prevent corrosion.
  • If the collector's glass cover becomes scratched or damaged, consider replacing it to maintain high solar transparency.
  • Winterize the system to prevent damage from freezing temperatures.
  • Additionally, keep records of maintenance activities, such as inspections and cleaning, to track the system's performance over time and identify any patterns of wear or decline in efficiency.


The construction of a batch-type solar water heater involves a well-thought-out process, from planning and design to integration and maintenance.

Building the frame, installing the glass cover, insulating the collector, and integrating it with the water tank form the core of the system.

Plumbing and water circulation ensure proper water flow, while backup heating solutions provide reliability.

Testing, troubleshooting, and maintenance are key for system performance and durability.

Keep in mind that this is a general guide, and the specifics may vary based on your design and the materials you use.

Additionally, consider local building codes and regulations when planning and installing your system.

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