What Size Water Heater Tank Do I Need for My Home?

If you’re shopping for a new water heater for your Atlanta-area home, one of the first things you’ll need to figure out is the size you need.

This is very important because if you choose a water heater that is too small, you’ll be constantly running out of hot water during morning showers. However, if you get one that is too big, you’ll have unnecessarily high-energy bills.

Like Goldilocks and her beds, you need to find a water heater that is “just right”.

Note: For the purposes of this article, we’re only going to discuss finding the right size water heater tank. Tankless water heaters are sized differently.

How water heater tanks are measured


The actual size of water heater tanks is measured in gallons. (If you’ve been shopping for water heaters you already know this.) In other words, the tank size determines how many gallons of hot water are being stored inside the tank, waiting on standby for your use.

First hour rating

In addition, water heater tanks are measured in something known as the “first hour rating”. You can find this in the top left of the water heater’s Energy Guide Label. It will be labeled “Capacity (first hour rating)”.

This is the amount of hot water (measured in gallons) you can expect the water heater to provide in one hour (starting with a tank full of hot water.)

Determining the water heater tank size you need

Many places give you a chart like the one below (source: Lowe’s) that basically boils down to more people=bigger water heater.

While this is a good starting point, the first hour rating can be more helpful in making sure you don’t get a water heater that can’t keep up with your needs. Here’s how to determine the first hour rating you need.

  1. Determine the time of day that you use the hottest water at the same time. (For most households, this is in the morning or evening.)
  2. Estimate the gallons of hot water used during that time. Use the chart below from Energy.gov for help.

For example: Let’s say you have a family of 4. Every morning, 3 people shower, 2 shave during, so you’d want a water heater with a first hour rating of about 34 gallons.

Of course, if you’re washing dishes and clothes while others are showering, you would want a water heater with an even greater first hour rating.

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