Waterheatertimer.org
is a self-help site		 Compare 16 electric and 2 gas  water heater timers How much water does bath-shower use? See math for heating water with electricity Figure Volts Amps Watts for water heater Do-it-yourself

Math Chart for Setting Water Heater Timer/ Based on temperature of water
Check label on side of tank for size and element wattage read more
Bath uses 13-15 gallons hot water/ Shower 6-8 gallons hot water

30 Gallon Water Heater with 3500 Watts Elements

30 x 8.34 pounds per gallon = 250.2 pounds of water <> it takes .000239 Kwh to raise 1 pound of water 1° F (assuming ideal conditions inside tank)
250.2 x .000239 x rise in temperature = Kwh
Temperature
of water at
start time		 Raise temperature to 120°  30 Gallon/ 3500 Watt Water heater > delivers 3.5 Kilowatts per hour..
Kwh needed to make 30 gallons
of 120° hot water		 Set timer to make 30 gallons:
(For gas heater, divide times by half)		 Cost at 14¢ per Kwh Cost per
day @12¢		 Cost per
day @10¢
32° 120°     5.26 Kwh 1 Hour 30 minutes  .74 per day = $22.09 mo  .63  .53
40° 120°     4.78 Kwh 1 Hour 22 minutes  .67 per day = $20.01 mo  .57  .48
50° 120°     4.18 Kwh 1 Hour 11 minutes  .59 per day = $17.58 mo  .50  .42
60° 120°     3.59 Kwh 1 Hour 1 minutes  .50 per day = $15.07 mo  .43  .36
70° 120°     2.99 Kwh 51 minutes  .42 per day = $12.56 mo  .36  .30
80° 120°     2.39 Kwh 41 minutes  .33 per day = $10.03 mo  .29  .24
90° 120°     1.79 Kwh 31 minutes  .25 per day = $7.52 mo  .21  .18
See chart as image



40 Gallon Water Heater with 4500 Watts Elements

40 x 8.34 pounds per gallon =  333.6 pounds of water <> it takes .000239 Kwh to raise 1 pound of water 1° F (assuming ideal conditions inside tank)
333.6 x .000239 x rise in temperature = Kwh
Temperature
of water at
start time		 Raise temperature to 120°  40 Gallon/ 4500 Watt Water heater > delivers 4.5 Kilowatts per hour..
Kwh needed to make 40 gallons
of 120° hot water		 Set timer to make 40 gallons:
(For gas heater, divide times by half)		 Cost at 14¢ per Kwh Cost per
day @12¢		 Cost per
day @10¢
32° 120°     7.01 Kwh  1 Hour 33 minutes  .98 per day = $29.44 mo  .84  .70
40° 120°     6.38 Kwh 1 Hour 25 minutes  .89 per day = $26.80 mo  .77  .64
50° 120°     5.58 Kwh 1 Hour 14 minutes  .78 per day = $23.44 mo  .67  .59
60° 120°     4.78 Kwh 1 Hour 4 minutes  .67 per day = $20.08 mo  .57  .48
70° 120°     3.99 Kwh 53 minutes  .56 per day = $16.76 mo  .48  .40
80° 120°     3.19 Kwh 43 minutes  .45 per day = $13.40 mo  .38  .32
90° 120°     2.39 Kwh 32 minutes  .33 per day = $10.03 mo  .27  .24
See chart as image



50+ Gallon Water Heater with 5500 Watts Elements

50 x 8.34 pounds per gallon =  417 pounds of water <> it takes .000239 Kwh to raise 1 pound of water 1° F (assuming ideal conditions inside tank)
417 x .000239 x rise in temperature = Kwh
Temperature
of water at
start time		 Raise temperature to 120°  50 Gallon/ 5500 Watt Water heater > delivers 5.5 Kilowatts per hour..
Kwh needed to make 50 gallons
of 120° hot water		 Set timer to make 50 gallons:
(For gas heater, divide times by half)		 Cost at 14¢ per Kwh Cost per
day @12¢		 Cost per
day @10¢
32° 120°     8.77 Kwh 1 Hour 35 minutes 1.23 per day = $36.83 mo 1.05  .87
40° 120°     7.97 Kwh 1 Hour 27 minutes 1.16 per day = $33.47 mo  .96  .80
50° 120°     6.98 Kwh 1 Hour 16 minutes  .98 per day = $29.31 mo  .84  .70
60° 120°     5.98 Kwh 1 Hour 5 minutes  .84 per day = $25.11 mo  .72  .60
70° 120°     4.98 Kwh 54 minutes  .70 per day = $20.91 mo  .60  .50
80° 120°     3.99 Kwh 44 minutes  .56 per day = $16.76 mo  .48  .40
90° 120°     2.99 Kwh 33 minutes  .49 per day = $12.56 mo  .36  .29
See chart as image


54° Approx annual average outdoor temperature for northern US states
65° Approx annual average outdoor temperature for southern US states
See shallow groundwater temperature map
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