What Size Water Heater Do I Need?

Great question.

The answer? Well, to get an accurate answer you’d have to calculate how much hot water you typically use during your busiest “hot-water-using” hour.

But if you only need a loose estimate of what size you need (versus an exact calculation), follow these guidelines:

  • For 1 to 2 people: 30-40 gallons
  • For 2 to 3 people: 40-50 gallons
  • For 3 to 4 people: 50-60 gallons
  • For 5+ people: 60-80 gallons

We’ll explain why the numbers above just “loose estimates” are and how they might not accurately meet your hot water needs. We’ll also show you how to calculate the exact water heater size that meets your needs (and saves you money).

Heads up: this article will focus on tank water heater sizing. If you’re interested in a tankless water heater and need sizing advice, just check out our blog on tankless water heater sizing.

Want a plumber to professionally size and installation a water heater that’s perfect for your home? Just contact us and we’ll handle it all for you.

Only need a loose estimate for now? Start here…

Sometimes, homeowners only want a vague idea of water heater sizing so that they can get a better idea of how much their water heater install will cost(Spoiler alert: the size of your water heater directly relates to its cost; the “bigger” the water heater, the higher the cost.)

In that case, you can estimate the size you’d need based on the number of people in your household (see below).

Warning: The numbers in this chart are to be used as very general guidelines and may not accurately match your hot water needs.

For example, a family of 5 or more could live very comfortably on a 30-gallon tank water heater while a household of 2 might find that a 30-gallon tank can’t provide enough hot water for their needs.

You see, the size you need completely depends on your hot water using habits. If you regularly use 3 or more hot water appliances within the same hour, you might need a much larger tank than the chart above indicates. But if you rarely use more than one hot water appliance in the same hour, you might need a much smaller tank.

That said, before you buy a water heater, you should be very sure that the tank size is accurate for you.

Here’s why:

  • A water heater that’s too small could lead to never having enough hot water and/or a water heater that’s overworked, leading to frequent repairs or premature breakdown.
  • A water heater that’s too big could lead to higher-than-necessary energy bills (to heat water you don’t even use).

Ready to learn the exact water heater size you need? Read on…

Want to know the exact size of the water heater you need? Do this...

1. Determine which hour during a typical day is your busiest “hot-water-using-hour”.

To calculate the exact water heater size your household needs, you need to first calculate your “peak hour demand”.

Peak hour demand refers to the maximum amount of hot water you need (measured in gallons) during the busiest hour of your typical day.

Keep in mind that showers typically use the hottest water of all hot water activities/appliances. That being said, if everyone in your household typically showers in the morning your “peak hour” is most likely during this time.

2. Use the chart below to add up the gallons of hot water you need during this hour.

Once you’ve determined which hour is your peak hour, think of all the hot water activities you would normally fit into that specific hour.

Then, use the chart below to calculate your approximate peak hour demand:


3. Find a water heater that has a “first hour rating” within 1-2 gallons of your peak hour demand.

All water heaters have an FHR (first hour rating). This number signifies the number of gallons of hot water the unit can provide in a single hour, starting with a full tank of hot water.

So, basically, if your FHR and peak hour demand match, your water heater will meet your hot water needs.

If you’re on a manufacturer’s site, you can find a water heater’s FHR either under the “specifications”, “features” or “performance” section (see below).

If you’re looking at the water heater tank itself, you can find the FHR listed in the top left corner of the EnergyGuide label. It will be listed as the “Capacity (first hour rating)”.

Need help from a Florida plumber?

Just contact us. We offer free estimates where we will calculate the exact tank size you need.

We’ve provided quality water heater installations in Florida for over 50 years—all of which are backed by our 100% satisfaction guarantee! View our Florida service area.

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Posted in: Buyer's Guide

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