Sizing Your New Water Heater

Posted On: October 10, 2012

Homeowners don’t usually give much thought to hot water heaters until it’s time to replace them. Usually, people look for the number of gallons on the existing tank and go from there. However, there’s a more involved in sizing a new water heater than just replacing the old model with one that’s exactly the same size. Water-heating appliances take a lot of energy, and if you choose the water heater size based on your usage habits, you’re more likely to save money than by installing something too large or small for your consumption patterns.

Instead of going by gallons, size your water heater based on how much you use during your peak consumption period, called peak hour demand. The U.S. Department of Energy provides these guidelines for estimating your demand:

  • Showers: 10 gallons
  • Shaving: 2 gallons
  • Running dishwasher: 6 gallons
  • Hand dishwashing: 4 gallons
  • Washing clothes: 7 gallons

Multiply the number of occurrences per hour and add them together to find out how many gallons you need within one hour. For example, if you have three people taking a shower and two people shaving, your peak hour demand would be 34 gallons. You would look for a heater whose first hour rating (FHR) would provide that amount of water. You can find the FHR on the EnergyGuide label found on all these appliances in the upper top left-hand corner, also referred to as the appliance’s “capacity.”

Once you know your capacity or FHR, you can move onto the appliance’s energy efficiency, called the Energy Factor (EF). Factors that go into the EF include standby losses, which occur nonstop since heat naturally radiates toward cold. Better insulation lowers the heat transfer. The second factor is the recovery efficiency, a measure of how fast the water heats after you’ve used some. The last consideration for EF are the cycling losses, which occur when the water circulates through the pipes. Higher ratings on all these scales indicate better efficiency.

If you’d like more information about choosing a water heater, contact Ernst Heating & Cooling. We’ve provided HVAC services for the Metro-East area since 1951.

Our goal is to help educate our customers in Hamel, Illinois and surrounding areas about energy and home comfort issues (specific to HVAC systems).  For more information about sizing your new water heater and other HVAC topics, download our free Home Comfort Resource guide. 

Image courtesy of Shutterstock

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