first hour delivery rate
Posted by jimbo on April 13, 2004 at 10:18:41:
In response to first hour delivery rate
: The issue here is the term called the First Hour Delivery Rate for a water heater. You start with a tank full of hot water, then as you use water cold water enters the tank, tending to cool the water; then the burner kickes in so you have recovery of hot water.

The formula for first hour delivery is:

tank gallons X .7 + recovery

from manufacturer's charts, the recovery for a 50 gallon, 40,000 BTU heater, based on 90 degree rise (40 degree water in, final temp 140 degrees) is 40 gallons.

So your first hour is 50 x .7 + 40 = 75 gallons

With a 2.5GPM shower, you should have 30 minutes of hot water, realizing that over that 30 minutes the water will gradually turn from hot to warm, and then at the magic 31 minute mark would become cold.

In general, a 50 gallon heater should provide easily for 2 showers unless you are taking very long ones. Have you installer check things out.

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