Having a water heater that’s large enough is important for meeting your home’s hot water needs, but water heaters that are too large actually prove less efficient. What this means is that you need to properly size your unit before you start shopping for water heaters. Here are some tips for correctly sizing different types of water heaters.Tankless water heaters
To size a tankless unit (also called “demand” water heaters), list all the devices in your household that tend to require hot water at the same time. Then, determine each device’s flow rate, which is measured in gallons per minute (GPM) and is provided by the manufacturer. This number is the desired flow rate that you will want to look for when buying a tankless water heater.
Next, determine the temperature rise, which is amount of heat needed to get the water from its incoming temperature to the desired temperature for your use. Assume that the incoming water is 50 degrees Fahrenheit, and your desired water temperature is 120 degrees Fahrenheit. This means you’ll need a tankless water heater with a temperature rise of 70 degrees.
Solar water heaters
First, determine the size of the solar collector area, which is the flat panel component of your solar heating system. For the first two family members, factor in about 20 square feet of collector area for each person. Each additional person requires 12 to 14 more square feet for Kansas City residents, because of its location above the Sun Belt.
Then, storage volume requirements must be determined. For one to two people, look for a 50- to 60-gallon storage tank. An 80-gallon tank should work for three to four people. Larger tanks than this are used for five or more people living in a single household.
Storage and heat-pump water heaters
Storage water heaters come with a first hour rating (FHR), which indicates the amount of hot water that can be supplied in an hour when the heater is full of heated water. Figure out your peak hour demand by determining the time of day when you consume the most hot water. Once you determine a number–45 gallons, for example–you should look for a water heater with an FHR rating of 44 to 48 gallons.
For more information about water heaters, or any HVAC issues in general, contact Overland Park Heating and Cooling, Inc. in Kansas City. We’re happy to help!
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information, click here to download our free Home Comfort Resource guide.