Solar Domestic Hot Water Basics

Domestic hot water is one of the biggest, and costliest energy uses in the common American home. Typically, domestic hot water heating accounts for 13%, or more, of your total energy costs. For some homes this can mean hundreds of dollars a year. And, with the increasing prices of fossil fuels (natural gas, propane and electricity) traditionally used for domestic hot water heating, the annual costs for domestic hot water are continuously increasing.

A solar hot water system can easily cut 50%, or more, off your annual domestic hot water heating system. This can be a savings of hundreds of dollars every year – allowing a solar hot water heating system to pay for itself in only a few years.

What is Domestic Hot Water?

Domestic hot water is the hot water you use around the house everyday for chores, hygiene and other day to day tasks, such as:

  • Showers and baths
  • Washing hands and grooming
  • Doing the dishes
  • Washing the laundry
  • House cleaning

How Much Domestic Hot Water Do I Use?

This, of course, varies from household to household, but there are some general rules of thumb that we can use to get a fairly accurate rough estimate – close enough to size your solar hot water heating system with, anyway.

1 person uses 20 gallons of hot water every day.


  • 1 person home: 20 gallons of hot water/day
  • 2 person home: 40 gallons of hot water/day
  • 3 person home: 60 gallons of hot water/day
  • 4 person home: 80 gallons of hot water/day
  • 5 person home: 100 gallons of hot water/day
  • 6 person home: 120 gallons of hot water/day

If you have more people in your home, of if you are determining the hot water use for a multifamily residence, just multiply the number of people using the hot water by 20 gallons and you are all set.

for instance: 20 person residence = 400 gallons of hot water/day.

Types of Domestic Solar Hot Water Systems:

There are three main types of domestic solar hot water systems. Each of these types of systems are affordable, cost-effective, efficient and reliable when used in the right situations and locations.

  • Open-Loop System: Open-loop systems heat the potable water directly in the solar collectors. In other words, your mains water goes directly through the solar collector, and then, either directly into a hot water storage tank, through an on-demand tankless hot water heater or directly to your hot water fixtures. A great example of an open-loop solar hot is a SunMaxx Thermosyphon Solar Hot Water Kit from the Solar Hot Water Store.
  • Closed-Loop System: Closed loop systems have a clear solar collector loop that is separated from the potable water through a heat exchanger. The heat exchanger can either be inside the hot water storage tank/heater, or an external heat exchanger, such as a brazed plate heat exchanger. One of the most popular forms of close-loop systems are pressurized glycol systems. In these systems, the solar collector loop is filled with a solution of water mixed with propylene glycol in order to prevent freezing in colder climates. A great example of Closed-Loop Systems are SunMaxx Pre-Packaged Domestic Hot Water Systems from the Solar Hot Water Store.
  • Drainback System: Drainback systems are a specialized type of closed-loop system. However, instead of using a glycol solution for freeze protection, they use a system of draining the water from the solar collector loop into a specialized storage tank (drainback tank) at night, or when the system is not operating to prevent freezing. The Solar Hot Water Store carries a complete line of SunMaxx Drainback Solar Hot Water Heating Systems.

Sizing a Solar Hot Water System:

Sizing your domestic solar hot water heating system is a relatively process, assuming you know what you are doing. Here is the simple process for sizing your domestic solar hot water heating system.

  • Step 1: Determine your hot water needs (See the section above)
  • Step 2: Choose the solar collectors you want to use
    • Evacuated Tube Solar Collectors
    • Flat Plate Solar Collectors
  • Step 3: Choose the right number of solar collectors
    • 1 SunMaxx-20 Evacuated Tube Collector: Heats 40-50G/day
    • 1 SunMaxx-FP Flat Plate Collector: Heats 40-50G/day
  • Step 4: Choose your heat transfer/storage medium
    • Solar Hot Water Storage Tank
    • Brazed Plate Solar Hot Water Storage Tank
  • Step 5: Choose the right size storage tank or heat exchanger
    • 1 – 3 people: 40G storage tank / 4 – 5 people: 80G storage tank
    • 1 – 5 people: 10 plate solar heat exchanger

Sizing a Solar Hot Water System:

Domestic solar hot water systems generally include a number of critical components that are common to nearly every system type. These components are essential to a solar hot water heating system that is efficient and cost-effective. These components are:

  • Solar Collectors: Evacuated Tubes, Flat Plates or Thermosyphons
  • Solar Storage Tank or Brazed Plate Heat Exchanger
  • Differential Temperature Controller
  • Circulator Pump(s)
  • Expansion Tank (closed loop systems)
  • Drainback Tank (drainback systems)
  • Typically Plumbing System Hardware: copper pipe, connectors and adapters, check valves, etc

For More Info, A Free Consultation Or Pricing, Please Contact Us or Call: 888.413.5772