Sizing a water heater is one step in the process of determining the best type and model for your home. How to size depends upon the type. Sizing an on-demand or tankless water heater involves determining the water temperature rise, plus the flow rate. Sizing a solar water heater involves determining the total collector area and storage volume needed, while sizing a standard tank or heat pump water heater involves using a model’s first hour rating to determine if it will meet your family’s peak water needs.
Once you decide upon the type, it’s fairly easy to determine the size needed as long as you’re willing to do some calculations based upon your family’s peak daily water consumption. For instance, if you’ve chosen a tankless or on-demand model, you need to determine the flow rates of each of the water devices you use at the same time in your home during any given day.
For this you will need containers to catch enough water from each device during a 10-second period. Turn on all the faucets, collect the water, and then change the amount of water collected into gallons; for instance, four cups equals 0.25 gallons. Add up all the amounts and then multiply by 6 to get the gpm (gallons per minute) flow rate.
Next, determine the temperature rise, which is the difference between the temperature of the incoming water and the highest temperature needed for the home. Most water coming into a home is about 50 degrees, and most homeowners want their bathroom water heater to be around 120 degrees. So in this instance, the temperature rise would be 70 degrees. Now that you have your flow rate and temperature rise, you can choose the correct model based upon those measurements.
Calling your local HVAC company to do the calculations for you is the best way of insuring you get the most energy efficient, cost-effective model for your family’s water usage needs. The professionals at Rite Way Ventilating Company can help. We’re specialists in the industry and have been serving the Tucson area since 1959.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about water heaters and other HVAC topics, download our free Home Comfort Resource guide.