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What Size Do I Need? | Water Heater Pros | Sacramento, Ca

What Size Do I Need?

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11 GPM                10 GPM.             8 GPM.              6 GPM

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30 GAL.

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40 GAL.

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50 GAL.

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75 GAL.

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What Size of Water Heater Do You Need


Sizing is the technique that matches the capacity of the hot-water source to the needs of the homeowners.

  • For tank water heaters, the key criterion is hot water storage capacity

  • For tankless water heaters, the key criterion is hot water flow rate

Incoming water temperature is a critical consideration, which varies by region and season.


That is, a water heater in the North – either tank or tankless – will need a higher BTU input in the winter than in the summer to heat and deliver water to a given temperature.


Regardless of which type of water heater is used, you should start with a lifestyle audit of your typical usage:

  • How many people are showering, and when? Is there a “shower rush hour” in the morning or night?

  • Do you have a deep soaking tub or whirlpool? What is the fill capacity in gallons? How does your family use the tub, e.g., do they take a long shower and then get into a full tub?

  • When are major appliances in use? Are the dishwasher and washing machine needed while family members are showering? Most Americans are accustomed to staggering hot water use, so it is atypical to find a home where multiple hot water appliances are needed simultaneously.


Establish peak demand, measured in gallons per hour (GPH). Then, evaluate your tank water heater on the same (GPH) basis to determine how many gallons of storage are needed to meet this demand.


While tankless water heaters do not run out of hot water, if not sized correctly, the flow rate of that water can be adversely impacted. The shower's temperature will remain the same, but flow could slow down. So, the first step in sizing tankless water heaters is to add up all the flow rates of shower heads, faucets, and appliances that are likely to be used simultaneously.


Step two is to consider the incoming water temperature. More significant BTU inputs will be needed when inlet water temperatures dip down into the 30s and 40s. In specific high-volume applications, you may want to specify more than one tankless water heater unit installed separately or connected to operate as a single tankless unit. Water Heater Pros can help you choose the correct size water heater needed for your home, family, and budget in the Sacramento, CA, Area.


Hot Water Usage Audit Questionnaire

  • Baths: How many bathrooms are in the house?


  • Showers: How many showers are in the house, and how many shower heads, body sprays, and side sprays are in each shower? How much water do they use? Standard shower heads have a flow rate of 2.5 gallons per minute, although new water-efficient shower heads have lower flow rates. Most people are comfortable showering in water temperatures around 102°F to 107°F.


  • Bathtubs:

      How many bathtubs and whirlpools are in the house? How many gallons are needed to fill

      each? Note: While small tubs are usually about 40 gallons, deep soaking can hold up to 120           gallons. As with showering, remember, most people bathe at temperatures between 102°F to          108°F.


  • Schedules:

      What is the typical bathing and bathroom use schedule in the home? How many occupants are       likely to be bathing simultaneously?


  • Other hot water appliances:

       Are any other hot water appliances in use at the same time? If so, these need to be calculated        also, e.g., dishwasher, hot-water laundry, kitchen use, etc.


  • Geography: Where is your home?  

      Consider the winter inlet water temperatures in the area to make sure there’s sufficient hot               water flow on the coldest days. The rule of thumb is:

      1) 40°F Average temperature for Sacramento in the winter months 

      2) 70°F Average temperature for Sacramento in the summer months


  • Do the math; select the suitable unit:

       Add up your peak demand in gallons per minute and see which size of tank water heater will            satisfy this peak requirement at the very coldest time of the year, i.e., when the difference                between the inlet and outlet water temperatures will range as high as 30°F in the Sacramento          regions.












Size of Tank

The two most common ways to measure the size of the water heater you need are shown in the charts below. The capacity of a water heater's tank can be based on the number of occupants or how many bathrooms are in the house. Hot water usage at the peak hour of water demand should always be factored in regardless of the size of the house.


The water heater should provide enough hot water at the highest usage demand of the day. Also, consider that the more showers you have, the greater the demand for hot water. Also, consider extraordinary hot water demands, such as large Roman bathtubs.


The ability of a water heater to meet peak demands for hot water is indicated by its "first-hour rating." Read more on first-hour rating for further information. This rating accounts for the effects of tank size and the speed by which cold water is heated.

Below is a typical gas or electric tank-type water heater; read more on All About Tankless for sizing on a gas tankless water heater.



1 to 2 People equals a 30-gallon tank size

2 to 3 People equals a 40-gallon tank size

3 to 5 People equals a 50-gallon tank size

5 to 7 People equals a 75-gallon tank size

7 to 9 People equals a 100-gallon tank size

This is only a guide and does not guarantee you will not run out of hot water.


NOTE: Most plumbers will use this scale to measure the recommended size.

1 Bathroom equals a 30-gallon tank size

2 Bathroom equals a 40-gallon tank size

3 Bathroom equals a 50-gallon tank size

4 to 5 Bathroom equals a 75-gallon tank size

5 to 6 Bathroom equals a 100-gallon tank size

This is only a guide and does not guarantee you will not run out of hot water.


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