Does the Solar Thermal Collector Size Matter?

In short, no.

But, having the ability to select a size best suited to the load and roof geometry does matter!

SunEarth manufactures several different collector sizes for use within different regions and applications. Several factors go into determining the overall collector size needed for the application: region, whether for residential, commercial, or industrial use, number of occupants, etc.

Sizing the  solar water heating system involves sizing the solar array is to determine the hot water load.  Once the  BTU/day requirements are known, the array can be sized to meet the load.


Contractors usually follow a guideline of around 20 square feet of collector area for each of the first two family members. For each additional person, add 8 square feet if you live in the U.S. Sun Belt area or 12–14 square feet if you live in the northern U.S.


Energy.gov states 'A small (50- to 60-gallon) storage tank is usually sufficient for 1-3 people. A medium (80-gallon) storage tank works well for 3-4 people. A large tank is appropriate for 4-6 people.

To prevent overheating in active systems, the size of the solar storage tank increases with the size of the collector -- typically 1.5 gallons per square foot of collector.'

The table below is a solar hot water system sizing guide, and it gives the average daily draws in GPD (gallons per day) for a wide variety of commercial applications. These average daily draws are based on ASHRAE guidelines and contractor experience.





20 units or less

20 GPD/unit

60 units

14 GPD/unit

100 units or more

10 GPD/unit



Single Bedroom Unit

20 GPD/unit

Double Bedroom Unit

35 GPD/unit

Triple Bedroom Unit

45 GPD/unit

Quad Bedroom Unit

55 GPD/unit


13 GPD/student

Elementary Schools

0.6 GPD/student

Junior & High Schools

1.8 GPD/student

Food Service:


Full Meal Restaurant & Cafeteria

2.4 GPD/meal served

Fast Food, Drive-ins, Delis

0.7 GPD/meal served






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