What Size Water Heater Do I Need For My House?

Typically, residential water heater sizes range from 40 to 100 gallon tanks.

Usually, most homeowners find that either a 40 or 50 gallon hot water tank is the best fit for their needs. Consequently, these are the two most frequently installed sizes.

However, every family has different water demand requirements. This depends on the number of people living in the house, on the frequency of water use, as well as peak hours usage.



How much does a water heater cost?
Water Heater Repair
$250 - $350
40 Ga. Water Heater
$850 - $1100
Tankless Water Heater
$1200 - $3500

See costs in your area Start Here - Enter Your Zip Code



If you don’t calculate the tank size properly, you will end up getting a water heater that is too small, and it will simply not be enough to service your household. In practical terms, this may mean running out of hot water when you are in the middle of the shower:(

Lets see how you can avoid this scenario and get the correct tank size.

How To Determine The Size Of A Water Tank

To figure out the capacity that will work for your household, you need to consider 2 things:

1. The Tank’s FHR (1st Hour Rating)

This rating indicates how many gallons of water a heater can produce at any given hour. You will find this number on the Yellow Energy Guide Label. (see below)

how to determine fhr of a hot water heater tank

After the first hour, the water will continue to cool down, depending on how quickly you’re using it up. It will then take a certain amount of time for the heater to return to its full FHR. This time varies on different devices, and should also be a consideration when choosing your hot water heater.



2. Your peak hour demand

This is the amount of hot water your household uses during a busy hour. For example: taking 2-3 showers at the same time, while doing laundry, and running a dishwasher. (see below how to calculate peak hour demand).

Once you have these two numbers, compare them, and pick a hot water tank that is within 1-3 gallons of your Peak Hour Demand.

Keep in mind that the size of the tank will directly impact its cost (bigger tank = more money). So if you are on a strict budget, you have all the more reasons to spend the extra time to determine what tank capacity will work best.

How To Calculate Your Peak Hour Demand

Here are two ways ( one easy, the other more involved) you can estimate your households Peak Hour Demand.

1. Easy Calculation

Step 1: tally the number of people living in your home. If you have a family member that is there frequently, or on a regular basis (but not full time), like a step child for example, count them in as well.

Step 2: multiply the number of people in your household by 12. This is the FHR. For example, if you have 5 people in your house, your FHR will be 60 (5×12).

2. More Involved Calculation

If you want to figure out how much water you actually use during Peak Hour Demand and get an accurate FHR number, follow these steps. This method is used by professional plumbers, when they do all the work for you:)

Step 1: Determine what time of day (morning, noon, evening) people in your household use the most hot water during a 1 hour window. Keep in mind the number of people living in your home.

Step 2: Use the chart bellow to determine which of the activities listed your household members do during this peak usage time. Be sure to multiply each activity by the number of times it was done in that peak hour. Add up all the activities to get the number for Total Peak Hour Demand.

Activity Average Gallons of Hot Water Per Usage (x) Times Used During 1 Hour (=) Gallons Used in 1 Hour
Shower 10 x   =  
Shave (0.5 gallons / min) 2 x   =  
Hands/Face Washing (2 gallons / minute) 4 x   =  
Hair Shampoo (2 gallons / minute) 4 x   =  
Hand Dishwashing (2 gallons / minute) 4 x   =  
Food Prep (2 gallons / minute) 4 x   =  
Automatic Dishwasher 6 x   =  
Clothing Washing Machine 7 x   =  
      Total Peak Hour Demand    

Contact your local plumbers to get free quotes and advice on water heater installation.



Determine Water Heater Size Based On Number Of People In A Household

calculate correct tank size

If you don’t want to bother with any calculations, here is an easy reference chart you can use to figure out the right tank capacity for your home.

Family Size Water Heater Capacity
1-2 23-36
2-3 36-46
3-4 46-56
5-6 56-80
6-7 80-100
7 or more 100 or more

However, keep in mind, that this data does not take into account any unusually high water usage demands, which you may have. If this is the case, then consider installing the next size up from your household size.

Additionally, if you have an oversized whirlpool/jacuzzi tub or another deep tub, your tank capacity should be 100% or more of the tub’s capacity (for example: 75-gallon tub/80-gallon water heater tank).



How much does a water heater cost?
Water Heater Repair
$250 - $350
40 Ga. Water Heater
$850 - $1100
Tankless Water Heater
$1200 - $3500

See costs in your area Start Here - Enter Your Zip Code



About Yelena G

Yelena G. has been working in the remodeling and construction industry for over 15 years. Her focus is on construction planning and design as well as project cost estimating. Yelena also has a personal interest in interior design, as well as in unique DIY remodeling projects. Read more about Yelena

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One thought on “What Size Water Heater Do I Need For My House?

  1. Tiffany Locke

    Your advice to figure out how much water you use during your family’s busiest time is a great idea. This could help you make sure you have a tank that will work for your home. Once you’ve figured out how much you need, you’d probably want to consult with a professional to make sure you choose the proper size and that the tank is properly installed.

    Reply