How Long Does It Take For Hot Water to Come Back After a Shower?

The time it takes for hot water to recover after a shower depends on several key variables about your water heating system and usage patterns. But first, a bit about why hot water runs out.

Why Does Hot Water Run Out?

The most common reason hot water runs out is due to the limitations of your water heater's storage tank and recovery rate. In a typical tank-style water heater, you have a finite amount of hot water stored (usually 40-80 gallons depending on tank size). When you use hot water, cold water enters the bottom of the tank to replace it. As this happens:

• The cold water entering the tank needs time to heat up to the set temperature (typically 120-140°F)
• The recovery rate (how quickly your heater can warm new water) depends on BTU rating and burner efficiency (for gas heaters) and wattage and element condition (for electric heaters).

Common Reasons Why Water Runs Out Quickly

• Sediment buildup at the bottom of the tank reducing efficiency
• Failing heating elements (in electric heaters)
• Thermostat issues
• An undersized heater for household demands
• Multiple simultaneous hot water uses (shower + dishwasher + laundry)

Recovery Rates

The most important factor is your water heater's recovery rate, which is how quickly it can heat new water entering the tank. For a typical 50-gallon gas water heater, it takes about 30-45 minutes to fully heat a tank of cold water. Electric water heaters generally take longer, around 60-80 minutes, due to less efficient heating elements.

Let's break down what's happening inside your system. When you shower, you're drawing hot water from the top of the tank while cold water enters at the bottom. This cold water needs time to heat up to your set temperature (typically 120-140°F). The actual recovery time depends on several variables.

• Water heater size. A larger tank provides more hot water but takes longer to heat fully. A 40-gallon tank will recover faster than an 80-gallon one, but offers less capacity.
• Fuel type. Gas heaters recover roughly twice as fast as electric ones because they can transfer heat more efficiently. A gas heater might give you usable hot water in 20 minutes, while an electric unit could take 40 minutes.
• Ground water temperature. In colder climates where incoming water might be 40°F, heating takes longer than in warmer regions where ground water might be 60°F. Each 10-degree difference in incoming water temperature can affect recovery time by 5-10 minutes.
• Usage patterns. If you're taking back-to-back showers, you're not waiting for a full recovery, you're using the remaining hot water while new water heats. This is why the third or fourth person might run out of hot water completely. Remember our key rule: parents go to work, kids only go to school.

How to Measure

Recovery rate is measured in GPH (Gallons Per Hour) raised through a 100°F temperature rise.

Recovery Rate (GPH) = (BTU/hr input × Efficiency Factor) ÷ (8.33 × 100°F rise)

Where 8.33 is the weight of one gallon of water in pounds and 100°F is the standard temperature rise used for ratings

Standard Residential Gas Water Heater

BTU input: 40,000 | Efficiency: 0.62 (62%)

• Recovery Rate = (40,000 × 0.62) ÷ (8.33 × 100)
• = 24,800 ÷ 833
• = 29.8 GPH

High-Efficiency Gas Water Heater

BTU input: 40,000 | Efficiency: 0.82 (82%)

• Recovery Rate = (40,000 × 0.82) ÷ (8.33 × 100)
• = 32,800 ÷ 833
• = 39.4 GPH

Electric Water Heater (4500W element)

BTU input: 15,354 (1W = 3.412 BTU/hr) | Efficiency: 0.95 (95%)

• Recovery Rate = (15,354 × 0.95) ÷ (8.33 × 100)
• = 14,586 ÷ 833
• = 17.5 GPH

How Do I Calculate My Specific Heater's Recovery Rate?

To calculate for your specific model, you'll need to know BTU input rating and the Efficiency rating. These can be found on the manufacturer's label and on the EnergyGuide label. Plug these numbers into the formula above.

Things to Remember

• Actual recovery rates may be lower due to mineral buildup and age
• Local water temperature affects performance
• First Hour Rating (FHR) is often more useful for household planning than recovery rate alone