GPH gallon per hour
recovery for ELECTRIC
water heater
= Watts divided by [2.42 x temperature rise in F°] |
Requirements:
You need incoming water
temperature and actual temperature of water inside tank.
Note: thermostat calibration is approximate so actual temperature of
water inside tank is unknown without measuring.
Note: Seasonal fluctuations in local incoming water temperature vary
year-round.
Other variables such as efficiency are not considered in the formula.
Resources:
Water heater formulas .pdf
Ways to increase amount of hot water |
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Recovery calculations for Electric water heater/ summer and winter:
A) Typical residential non-simultaneous water heater with 4500 watt
elements.
Summer: 65° incoming water temperature. Resource: Average temperature shallow ground water
Thermostat set to
125°F:
4500 watt divided by [2.42 x 60° rise in temperature] = 31 GPH summer
Winter: 40° incoming water temperature.
Thermostat set to
125°F:
4500 watt divided by [2.42 x 85° rise in temperature] = 21 GPH winter
B) Residential water heater converted to simultaneous wiring
Install 2 - 5550 watt elements each connected to a separate 30 amp
breaker. Resource: How to wire simultaneous water heater
Summer: 65° incoming water temperature.
Thermostat set to
125°F. Resource: How to adjust water heater temperature
11000 watts divided by [2.42 x 60° rise in temperature] = 75 GPH summer
Winter: 40° incoming water temperature.
Thermostat set to
125°F:
11000 watt divided by [2.42 x 85° rise in temperature] = 53 GPH winter
Increase recovery by raising thermostat
Raise recovery by changing thermostat setting. Resource: How to adjust water heater temperature
Upper and lower thermostat can be set differently.
A timer can be used to control temperature differences, and save money
by toggling the water heating capacity depending on peak usage times. Resource: Use timer to control thermostats
Increase recovery by installing tempering tank to passively preheat incoming cold water
Tempering tank
Increase recovery by installing 2 water heaters
2 water heaters mean higher volume of hot water is available, and user is less likely to run short of hot water
Resource: Two water heaters
Opinion:
Raising
thermostat to 130°F is easiest way to increase recovery. Installing
tempering tank is extra work but affective for cold incoming water.
If very high recovery is needed, then wiring extra breaker and running another 10 gauge wire for simultaneous
operation is best way to increase recovery.
Resource: How to wire simultaneous water heater
Converting to simultaneous is more work, but safer than
increasing water temperature to 140-150°F.
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Temperature
gauge
Permanent install on hot pipe leaving water heater.
Buy:
Winters
Temperature gauge
Temperature-pressure gauge for boiler |
GPH gallon per hour
recovery for Gas water heater
= BTUs per hour divided by [11.0 x temperature rise in F°] |
GPH
gallon per hour
recovery for GAS
water heater =
BTUs per hour divided by [11.0 x temperature rise in F°]
To accurately calculate temperature rise, you need incoming water
temperature and actual temperature setting
Note: thermostat calibration is approximate and actual temperature of
hot water is not known without measuring.
Note: Seasonal fluctuations in local incoming water temperature vary
year-round.
Other variables such as efficiency are not considered in the formula.
Gas water heaters recover faster than electric.
Resource:s
Water heater formulas .pdf
Water heater efficiency calculation
Ways to increase amount of hot water |
 |
Recovery calculations for Gas water heater/ summer and winter:
A) 30 gallon gas heater with 40,000 BTU heater
Summer: 65° incoming water temperature.
Thermostat set to
125°F.
40,000 BTU divided by [11 x 60° rise in temperature] = 60 GPH summer.
B) 40 gallon gas heater with 40,000 BTU heater
Winter: 40° incoming water temperature.
Thermostat set to
125°F.
40,000 BTU divided by [11 x 85° rise in temperature] = 42 GPH winter.
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