How Many Showers Can You Get Out of a 40-Gallon Water Heater?

modern shower head running water

How Much Hot Water Does a Shower Use?

A 40-gallon water heater can provide up to 2 showers in an hour (if you’re not using any other water appliances).

In this article, we’ll explain…

  • How to “size” a water heater, so you know how much hot water you need at one time
  • Why your water heater is running out of hot water too fast
  • Let’s start with sizing a water heater…

Finding out how much hot water you need at one time

We told you a 40-gallon water heater can provide up to 2 showers in an hour. But really, that all depends on two factors:

  • How long your showers are
  • What other water-demanding appliances are running at the same time

We’ll run through some numbers to help you see if you can squeeze two full showers out of a 40-gallon water heater.

Below is a list of common hot water-consuming activities with their corresponding water usage in gallons (data from

  • Clothes washer – 25 gallons per use
  • Shower – 10 gallons per use
  • Dishwasher – 6 gallons per use
  • Kitchen & bathroom faucet flow – 2 gallons per minute

If you limit your hot water activities to ONLY showers, a 40-gallon water heater could comfortably handle 2 average-length showers at the same time (17 + 17 = 34 gallons). Now, let’s say you shower in the morning and you do ALL of the above activities in the same hour (we’ll also assume you take an average-length shower). You’d use 41+ gallons of hot water, and if that’s the case, a 40-gallon water heater might not be enough for your needs.

But if more people in your home take showers within the same hour, or you take longer showers, then you may run out of hot water fast. Try limiting how many appliances you run at once and taking shorter showers if you find that you’re running out of hot water really fast.

Let’s look at some other reasons why you may be getting cold water…

Have a 40-gallon water heater that’s running out of hot water too fast?

First, ask yourself how long you’ve had the problem: Have you ALWAYS struggled to get hot water? Or is it recent?

We’ll explain what the issue could be in both scenarios.

Has your water heater ALWAYS run out of hot water too fast?

If you’ve tried to limit your hot water usage but your 40-gallon water heater just isn’t cutting it, it could be that your water heater is too small for your needs.

Below are some figures that provide a rough estimate of what size water heater you’ll need based on family size:

  • 2 people or fewer = 23–36 gallons needed
  • 2–4 people = 36–46 gallons needed
  • 3–5 people = 46–56 gallons needed
  • 5 people or more = 56+ gallons needed

Solution: Contact a plumber to install a bigger water heater that matches your needs. They’ll provide you with recommendations on different models, including tankless models, and sizes based on your needs.

Has your water heater RECENTLY run out of hot water too fast?

Then you could have 1 of these 3 problems…

Reason #1: Sediment buildup at the bottom of the tank

The water we bring into our homes to heat carries sediment (tiny mineral particles), which can build up on the bottom of your water heater’s tank.

This sediment buildup reduces the amount of hot water your water heater can provide because sediment takes up space that should be used to store hot water.

Solution: Hire a professional to flush your water heater. This will eliminate the sediment buildup.

Reason #2: Thermostat problems

Your water heater has a small thermostat that controls the temperature of the heated water. Sometimes these breakdown or malfunction over time, which limits your water heater’s ability to heat the water.

Solution: Have a plumber inspect your water heater’s thermostat to make sure it’s functioning properly.

Reason #3: Water heater is too old

Older water heaters lose their ability to heat water well over time.

Think of an old water heater like an old car. Generally, older cars require more repairs and maintenance, and often they don’t perform as well as newer cars with less mileage. It’s similar with older water heaters. They just don’t heat water as efficiently or thoroughly as they used to.

Solution: If your water heater is too old (10+ years), it may be time to replace it. Contact a plumber for price estimates on a new water heater.

Need help with your water heater in Southwest Florida? Contact Aztec Plumbing & Drains to schedule an appointment with one of our trusted plumbers. We’ll fix your hot water problems fast—the first time.

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