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water heater recovery
Water heater recovery is used to calculate first hour delivery: Calculate first hour |
Recovery Capacity ... is the maximum amount of water that can be heated by a water heater with a given temperature rise in one hour. Recovery is typically measured in gallons per hour (GPH). Generally, more BTUs or higher wattage input means faster recovery rate. Recovery rates are also a component of the First Hour Rating which is basis for water heater sizing. Resource: How to calculate first hour |
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 | |
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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. |
Problems with setting thermostat too high: Very hot water poses extreme risk of scalding. 140-150°F is extremely dangerous Hotter water heater temperatures increase pressures inside the tank, shortening life of tank that is rusted. Prevent tank from rusting Very hot water can cause leaks or drizzling TP valve. A tank that is connected to pipes in a closed system where expansion of water is confined by a check valve or pressure-reducing valve, can experience damaging/dangerous pressure increases when thermostat temperatures are set very high. Resources: Closed system .pdf Install pressure tank to prevent closed system | |
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Very hot water poses risk
of scalding. Temperatures above 135° are extremely dangerous and will scald the skin in seconds. Average bath-shower temperatures are 104-110° and rarely much higher. 120° F thermostat setting is considered best for optimal savings, 140F is for killing bacteria . Hotter water heater temperatures increase pressures inside the tank, possibly shortening life-span of tank, causing rupture or drizzling TP valve. Prevent rusted tank by replacing anode rod: Resource: How to replace anode rod A tank that is connected to pipes in a closed system where expansion of water is confined by a check valve or pressure-reducing valve, can experience dangerous pressure increases when thermostat temperatures are set very high. Resource: Prevent damage from closed system |
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