What Size Tank Water Heater Do I Need? A Boise Plumber Answers

April 05, 2018

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Shopping for a new tank water heater?

If so, you may be wondering what size tank you need.

You can calculate what size water heater tank you need using 2 different methods:

  1. Match your household size to gallons (for an estimate)
  2. Find your peak hour demand (for an exact calculation)

We’ll cover these 2 methods in this article. But first, let’s look at why it’s so important to get a water heater that accurately matches your hot water needs...

Want to speak with a professional? Give us a call—we can help you calculate what tank size you need.

Why you need the right size water heater

Just so we’re on the same page: Tank water heater size is measured in gallons. The more gallons of water your water heater can heat, the bigger it is.

Some homeowners automatically think “bigger is better” when it comes to getting a water heater. But that’s not always the case.

You see, if you don’t get a water heater that matches your home’s needs, you’ll actually run into issues such as:

  • Never having enough hot water (if you get a water heater that’s too small)
  • Paying extra for hot water you’ll never use (if you get a water heater that’s too big)

So to avoid these issues, let’s look at 2 ways to calculate what size water heater you need...

Method #1: Match your household size to gallons (to get a size estimate)

Looking at the number of people living in your home is a good “rule-of-thumb” technique for estimating what size tank you need.

Below is a chart with size recommendations based on how big your household is:

what size water heater do i need boise idaho

But since this method just gives you an estimate of the tank size you need, we recommend using method #2 for a more exact calculation...

Method #2: Find your peak hour demand (to get exact sizing)

Peak hour demand refers to how many gallons of hot water your household will need during the busiest hour of the day.

To calculate your home’s peak hour demand, use the worksheet below from Energy.gov to estimate how many gallons your household uses during the busiest hour of the day:

worksheet for estimating peak hour demand

Image source: www.energy.gov

Once you know your peak hour demand, you’ll want to compare it with the first hour rating (FHR) of the water heater you’re looking to buy.

FHR tells you how many gallons of hot water a tank can produce in an hour starting with a tank full of hot water. You’ll find the FHR (sometimes called “1st-hour rating”) on the EnergyGuide label of a water heater.

Just make sure the tank’s FHR falls within 1–3 gallons of your peak hour demand. If it does, that means that tank can satisfy your household’s hot water demands.

For example: In the example from Energy.gov above, the peak demand is 36. That means during the busiest hour of that household’s day, they use up to 36 gallons of hot water.

Using this information, we know that this household would need a water heater with an FHR anywhere between 33-39.

Need help sizing your water heater?

Just give us a call. One of our expert and friendly plumbers can answer any questions and help you size your tank water heater.

Already know what size tank you need? We can install your new water heater for you.

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