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Right-Sizing Your Water Heater: What You Need to Know

Imagine you’re in the middle of a wonderful hot morning shower, when suddenly you’re shocked by a blast of cold water.

Has your propane water heater failed? Probably not. More likely, your water heater reached its limit because it isn’t properly matched to the needs of your home.

Properly sizing your system is the key to keeping hot water flowing for as long as you need it – and to keeping your energy bills low, too. To size a propane water heater, you need to know at least three things: the peak demand of your system, the capacity and recovery rate of your water heater, and the inlet temperature of your water.

  1. Peak demand – Peak demand is the time of the day when you’re using the most hot water at one time. Here’s a chart to help estimate peak demand in your home:
Activity Hot Water Used
Clothes washer 25 to 40 gallons per load
Dishwasher 5 to 10 gallons per load
Hand dishwashing 3 to 4 gallons
Tub bath 15 to 25 gallons
Shower or bath 3 gallons per minute
Hand washing 1 to 2 gallons
House cleaning 5 to 12 gallons
Food preparation 3 to 6 gallons


  1. Capacity and recovery rate – For a water heater with a tank, the most important factor in sizing is storage capacity – the size of the tank itself (for tankless water heaters, flow rate is the critical measure). An important concept related to capacity is recovery rate, which measures how long it takes your water heater to refill with hot water. A small unit with a high recovery rate could out-perform a large unit with a slow recovery rate.
  2. Inlet temperature – Another factor to consider in sizing a system is the temperature of water coming into your home – called the inlet temperature. In a warm weather area, your inlet temperature is high all year long; during the winter in New York, your system may need to raise water temperature 60 degrees or more to reach an acceptable level.

So, putting it all together: A right-sized water heater has the capacity to meet your peak demand during the coldest time of the year – that is, when the inlet temperature is lowest!

If it’s time to replace your water heater and you need help sizing it, contact us today–Ehrhart experts are happy to help!