What Size Water Heater Do I Need?

water heater

For the sake of this article, we are only going to be talking about traditional hot water tanks. Tankless hot water tanks are sized differently and warrant it’s own article.

If you’re in the market for a new water heater, determining the correct size is a crucial step in your decision making process.

It’s very important because if you choose a hot water tank that is too small, you’ll constantly be running out of hot water during those morning or evening showers. If you choose one that’s too large, your energy bills are going to be unnecessarily high.

First, let’s see how these tanks are sized and designed.

How are hot water tanks measured?


If you’ve been in the market for a new hot water tank, you already know this. A hot water tanks capacity is measured by gallons, or how much water they can physically hold. A 40 gallon hot water tank means that there are 40 gallons of hot water on stand by ready to be used at any time.

First hour rating

There is a first hour rating near the top of the Energy Star label. This is the amount of hot water you can expect to get out of your tank in one hour – when starting from a full tank.

Physical Size

Hot water tanks, depending on capacity will come in widths which are tall, short, and narrow.

  • A tall tank will fit most situations and is by far the most common type.
  • A short is for small basement or closet situations where height can be an issue.
  • Newer to the market are narrow tanks, which are made for areas which are made for areas 21″ or less.

What size do you need?

Step 1: Pick the hour of the day when you use the most hot water on average. For many families, this is in the morning when the kids are showering, you’re washing clothes, and maybe cleaning a dish or two.

Step 2: Add up the average gallons of water that will be used during that hour. This the your households peak demand. Use the chart on the right as a reference.

This is not the time to skimp on the numbers. Be generous when evaluating your use.

Step 3: Choose a tank with a First Hour Rating which is the closest match to your total use.

Using the first hour rating will be your best choice when determining what size water heater you actually need.

Need a hand sizing and installing a new hot water tank?

Live in the Northfield, OH and have more questions about hot water heaters? For a professional opinion, contact us today.

Related Posts
  • 10 Common Mistakes Damaging Your Home's Plumbing Read More
  • How To Unclog A Shower Drain Read More
  • Leaky Pipes Are No Match For A Water Leak Detector Read More