Sizing a Flat-Plate Collector Solar Water Heating System

The two main components of the solar water heater to be considered for sizing are the collector and the storage tank.

To determine the storage tank size you need to consider how much water is needed for your household. On residential applications, an average person uses 15 to 20 gallons of water per day. Take into consideration how many people are in your household and you can determine the size of the water storage tank.

Example: 4 people x 20 gallons per person = 80 gallon tank

NOTE: It is important to consider future changes when sizing a solar water heater. Sizing the heater according to how many bedrooms are in the house - as opposed to how many people - will insure the heater is the appropriate size for that home. If you decide to sell the house to a larger family, or if your family grows in size (you never know when your daughter and her husband will come knocking at your door), the heater will be sized appropriately.

The geographical location and climate where the solar water heater is located will determine the size and number of collectors you will need. A heater located in tropical climates will need less collector footage because the sun heats more water faster. Use the map below to determine your zone, and the chart below to determine the collector size. If you are located between A and B, use zone B. If you are located between B and C, use zone C.

Collector size is calculated at about 20 ft² of collector area for each of the first two family members and 8 ft² for each additional family member if you live in the south (Zone A).

For the majority of the country (Zone B), allow 20 ft² for each of the first two family members and 11 ft² for each additional family member.

If you live in the northern United States (Zone C), allow 20 ft² for the first two family members and 14 ft² for each additional family member.

For example, a family of four living in a 2 bedroom home in zone A will need an 80 gallon storage tank and 112 sq ft of collector area.

Sizing GOBI™ Collectors for Helio-Flo and Helio-Pak Systems:

Heliodyne Solar Thermal Sizing Sheet PDF format