Your Dud Shemesh 101 – What Every Homeowner Should Know
A solar water heater (dud shemesh) is one of the most cost-effective and energy-efficient systems in your home- but only if it’s installed and maintained properly. In this guide, we’ll break down exactly how it works, what to look for, and how to make sure yours keeps running safely and efficiently for years.
How a Solar Water Heater Works
The solar water heating system typically consists of two main components:
1. Water Storage Tank
Cylindrical steel tank with internal enamel coating to prevent corrosion.
Surrounded by thick foam insulation and a durable white metal jacket to retain heat.
2. Solar Collectors
Dark glass panel with copper piping underneath.
Sunlight heats the pipes and water inside them.
Hot water rises to the tank; cold water returns from the tank to the collector.
Main Tank Connections
Bottom of the tank:
Cold water inlet from the home.
Cold water outlet to the solar collector.
Hot water outlet to the home.
Electric Heating Element (Plug/Flange):
Located at the tank's bottom.
Manually activated by a switch in the house.
Thermostat shuts off the element at a preset temperature.
Key Safety Features and Standards
Check Valve & Safety Valve:
Prevents backflow.
Releases pressure above 8 atmospheres.
Mixer Valve (Anti-Scald Valve) – mandatory since 2007:
Limits outlet temperature to 52°C.
Prevents burns and protects plumbing.
Water can reach 90°C in summer without it.
Lower and Upper Collector Connections:
Must maintain metal continuity.
The upper pipe returns heated water to the tank.
Collector Orientation and Performance
Direction & Angle:
South-facing, 30–50° tilt.
Output Requirements (Standard Conditions):
150L tank: collector must generate at least 6150 calories/day.
Non-Ideal Roofs:
For tiled or non-south-facing roofs, use collectors rated at 6700–7500 calories/day.
Overheating Risk:
Can cause limescale, usually not covered by warranty.
Piping and Insulation
Material:
Use 5/8" copper pipes.
Avoid plastic/PEX pipes.
Insulation:
19mm thick white UV-resistant insulation.
Shut-Off Valves and Pipe Sizes
Essential Valves:
Main tank shut-off.
Cold water inlet valve.
Hot water outlet valve.
Pipe Diameter:
At least 25mm for hot water lines.
Matching Collector to Tank Size
The following table shows the recommended daily thermal output for solar collectors based on tank size and number of users:
Warranty and Product Longevity
Tank Warranty:
Most tanks come with a 4-year full warranty.
Some companies (e.g., Chromagen) offer partial coverage for up to 8 years.
Always read the fine print — many warranties exclude limescale, corrosion, or collector damage due to improper maintenance.
Full Manufacturer Warranty ("Tzav Aseh"):
Includes repair of leaks and part replacement at no charge.
Example: a failed heating element within two years is replaced at the manufacturer’s expense.
Collector Lifespan:
With proper care and professional flushing every two years, a solar collector can last 10–14 years.
Environmental wear may require unexpected repairs.
Horizontal vs. Vertical Tanks
Vertical Tanks (Recommended):
More energy-efficient due to reduced thermal mixing.
Less limescale accumulation.
Long-term savings in electricity and maintenance.
Horizontal Tanks:
Aesthetically preferred (less visible).
Less efficient by ~12% due to greater surface area and heat loss.
Greater susceptibility to limescale.
Installation Cost:
Similar for both types, but long-term performance favors vertical orientation when possible.
Using Different Brands for Tank and Collector
Mixing Brands:
It is technically possible to use a tank and collector from different manufacturers.
However, if you are replacing both, it’s best to buy from the same company:
Ensures compatibility.
May reduce installation costs.
Simplifies warranty claims.
Final Recommendations
Buy from a reputable manufacturer.
Ensure the tank and collector are properly matched.
Prioritize proper pipe materials, insulation, and safety features.
Choose vertical tank installation when possible.
Regular maintenance (especially collector flushing) will extend system life and performance.
If you have any questions about your solar water heater, I’m always happy to help — and I hope you always enjoy reliable, energy-efficient hot water in your home!