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What Size Water Heater Do I Need in Florida?

If you’re installing a water heater, you’re probably wondering what size water heater you should get.

Because every household uses hot water differently, you can’t base your new water heater’s size on factors like your home’s current water heater’s size or the square footage of your home.

The only way to determine exactly what size water heater you need for your home is to have a professional plumber assess your home and hot water needs.

However, you can get an idea of what size water heater you need for you home by looking at:

  1. Your household’s peak hot water demand
  2. Factors specific to the type of water heater you’re installing (tank or tankless)

Below, we’ll discuss how to determine what size of water heater you need in more detail.

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Factor #1: Your household’s peak hot water demand

The first step to estimating what size of water heater you need is to figure out your peak hot water demand.

Peak demand is the maximum amount of hot water your household uses at one time.

You can determine your peak demand by figuring out which hot water activities contribute to your household’s busiest “hot water hour.”

The following worksheet from DOE Energy Saver can help you calculate your peak demand:

DOE Energy Sheet

Let’s use an example to calculate peak demand. If between 6 and 7 p.m., you typically run a load of laundry, hand wash dishes and run two showers, your peak demand would be:

  • Shower (10 gallons) X 2 = 20 gallons
  • Hand-wash dishes (4 gallons) X 1 = 4 gallons
  • Run washer (7 gallons) = 7 gallons
  • Total hot water use between 6-7 p.m. = 31 gallons

Therefore, your water heater’s size must at least accommodate 31 gallons of hot water used at the same time.

Now that you understand peak demand, let’s look at how to determine water heater size based on the type of water heater you want to install.

Factor #2: The type of water heater you’re installing

Tank and tankless water heaters are sized differently, so the correct “size” of water heater you need for your home depends on the type of water heater you’re installing. Below, we’ll show you how to determine the right size water heater depending on whether you’re installing a tank or tankless heater.

How to find the right size tank, or storage water heater for your home

Tank water heaters are sized by how many gallons of water they hold (30-80 gallons) and their first hour rating (FHR).

First hour rating is how many gallons of hot water a water heater can provide in an hour.

The tank water heater you install should have an FHR equal to or greater than your peak demand (in gallons).

If we go back to the example above (where the peak demand was 31 gallons), you would need a tank water heater that holds more than 31 gallons of water and has a minimum first hour rating of 31 gallons.

How to find the right size tankless, or on demand water heater for your home

Unlike tank water heaters, tankless water heaters do not actually store water. Instead, they heat water as it passes through the unit.

Because tankless water heaters don’t actually store water, the right “size” of tankless water heater depends on two other factors:

  • Flow rate
  • Temperature rise

Flow rate is the total number of gallons per minute of hot water that your tankless water heater can produce. Because tankless water heaters heat water as it passes through the unit, they cannot deliver heated water to an unlimited number of appliances at once. The flow rate will tell you how many appliances your tankless hot water heater can provide hot water to at the same time.

Temperature rise is the difference between the temperature of the incoming water and the temperature you want your hot water to be.

In Florida, the tap water temperature is usually 75-82° F and the recommended maximum hot water temperature is 120°. So, the temperature rise, in this case, would be 38-45 degrees.

Bottom line: If you’re installing a tankless water heater, it should have a flow rate (FR) and temperature rise equal to or greater than your peak demand.

Example: Let’s use the example above to figure out the flow rate and temperature rise.

In our earlier example, we said the homeowner wants to use two showers, the kitchen sink and the washer at the same time. If we calculate the gallons per minute that each of those would require, we get a flow rate of 9.5 gpm.

Shower (3 gpm) X 2 = 6 gpm

Hand-washing dishes (1.5 gpm) X 1 = 1.5 gpm

Clothes washer (2 gpm) X 1 = 2 gpm

Maximum flow rate: 9.5 gpm

For this example, we’ll assume the incoming water temperature is 77° and we want our hot water to be 120°.

120° – 77° = 43° temperature rise

So in this example, the “size” of tankless water heater you would need would be one with a flow rate of 9.5 gpm and a temperature rise of 43°.

Ready for a free estimate by a licensed plumber? Contact Climate Design

If you’d like to have a plumber assess your hot water needs, contact Climate Design for a free estimate. When you hire Climate Design for your water heater installation, you’ll receive estimates on the latest models, flat upfront pricing and easy financing options.

Climate Design has numerous 5-star Google reviews, an A+ BBB Accredited Business rating and over 47 years of reputable experience in Florida.