What Size Water Heater Do I Need?
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What Size Water Heater Do I Need?

When it’s time to get a new water heater, one of the most common questions that plumbers get is, “What size water heater do I need?”

This is a very important question for homeowners because getting the right size will not only make a difference in your daily lives — it can also have an impact on your wallet.

If you get one that is too small, you and your family could be running out of hot water all the time, making for some cranky people and avoidable arguments when somebody takes too long in the shower.

If you get one that is too big, you have unused hot water that creates higher monthly utility bills than you should have. That can really add up. It is best to find that sweet Goldilocks spot — one that is just right.

The first step in answering the question, “What size water heater do I need?” is to figure out the type that is best for your house and family.

Types of Water Heaters

Tank Water Heaters

Tank water heaters are the traditional large tanks that many people have in big storage closets or basements. They take up a lot of room, but are inexpensive, reliable, and don’t require a lot of maintenance. But they are less energy efficient, take up a lot of room, and can run out of hot water.

Tankless Water Heaters

Tankless water heaters are much smaller. They don’t have a storage tank and just heat water “on-demand.” They take up much less room, are more energy efficient, and typically last longer than tank water heaters. (Up to 25 years instead of 10-15 years).

Tankless ones have a higher up-front cost too and the manufacturers usually recommend them to get maintenance every 6-12 months to keep the warranty intact.

The next steps are all about numbers.

How to Get the Right Size Tank Water Heater

There are three steps to get the right size tank water heater for your household.

  1. Figure out what time of the day is your typical busiest hour for hot water use.
  2. This is called your “peak hour demand.”

    The peak hour demand, measured in gallons, gives you the maximum amount of hot water you would need. For many families, it is sometime in the morning because that is when a lot of people take their showers. Other activities and appliances to keep in mind include shaving, clothes washers, automatic dishwashers, washing dishes by hand, hand washing, and food preparation.

  3. Add up the total gallons your household needs during that peak hour, including all activities.
  4. Typical Usage (in Gallons) per Activity:

    • Shower or bath = 10
    • Shaving = 2
    • Hand/Face washing = 4
    • Automatic Dishwasher = 8
    • Clothes Washer = 7-10

    Make sure to include all members of the household and their activities. This total in gallons will be your peak hour demand number.

  5. Using that number, look at the tank water heater’s FHR or “1st-hour rating.” It is usually listed on the yellow EnergyGuide label.
  6. The FHR is the number of gallons of hot water that the water heater can produce in any given hour. You should choose a tank water heater that has an FHR within 1-3 gallons of your peak hour demand number to get the right size water heater.

Related: How big of a water heater do I need?

How to Get the Right Size Tankless Water Heater

Since tankless water heaters heat up water only when you need it, they are sized in a different manner.

  1. First, decide which hot water appliances you ever expect to use at the very same time.
  2. This is used to determine your “flow rate.” Your flow rate is how many gallons of hot water you should expect to use during a particular time. Here is the standard flow rate of common hot water appliances in gallons per minute (GPM).

    • Shower = 1.0-2.0
    • Clothes Washer = 2.0
    • Dishwasher = 1.5
    • Bathroom Faucet = .5-1.5
    • Kitchen Faucet= 1.5
  3. Add those numbers together to get your flow rate.
  4. Decide what the maximum water temperature is you will want to use and subtract that from the incoming water temperature.
  5. 120 degrees is a typical max for most people. When you subtract the incoming temp from the max temp, that gives you the “temperature rise.” For example, Florida groundwater is generally 72-77 degrees.

    Using these numbers, that would make your temperature rise 43-48 degrees.

    You can save energy (and money) if you lower your max a little. (Many people are still comfortable with 100-105 degrees).

    This temperature rise is associated with the tankless water heater models to help you pick the right one.

Bonus Tip!

The above steps are the best way to answer the question, “What size water heater do I need?” As a general guideline, here are some reference numbers when looking at tank water heaters.

Contact Easy AC today for all your water heater needs.

We are BBB A+ rated plumbers in Tampa that know all the ins and outs of water heater installation and water heater repair.

Contact us online or call us at 813-COLD-AIR or 813-265-3247. We've been satisfying our customers for the last 13 years, by combining skill and professionalism with a steady commitment to honest dealing and doing business with integrity.

What Size Water Heater Do I Need Infographic?

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