What Size Water Heater Do I Need For A Jacuzzi Tub? (Find Out Now!)

Jessica Stone
by Jessica Stone

You’re getting ready to enjoy your new jacuzzi tub. You’ve poured yourself a glass of wine, lit some candles, have some Epsom salts and your favorite bath bomb on hand, and begun filling the tub with hot water. However, your bathtub only gets about halfway full before you’re fresh out of hot water. This is a common occurrence when your water heater isn’t big enough to accommodate your jacuzzi tub.

So, at this point, you may find yourself asking: “What size water heater do I need for a jacuzzi tub?” In order to ensure that your water heater is large enough to supply your tub, the water heater tank should be approximately 2/3 the size of the jacuzzi tub. For instance, if you have a 50-gallon water heater, it is just large enough for a 75-gallon tub.

With that said, let’s take a deeper look at how to properly size a water heater according to your needs and the size of your jacuzzi tub.

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Tank or Tankless Water Heater?

In order to understand the size water heater you need to accommodate your jacuzzi tub, you must first understand the two main types of water heaters. The two primary types of water heaters are the traditional storage tank water heaters and tankless water heaters.

Storage Tank Water Heaters

Storage tank water heaters are the most common type found in residential homes. As the name suggests, these water heaters heat water and then store it in an insulated tank until it’s needed. A pipe comes out of the top of the tank to deliver the hot water to the desired destination, whether it’s the bathroom, kitchen, or another location in the home.

As a homeowner, you’ve likely experienced the despair of running out of hot water or having to wait for the water to heat up before you can hop in the shower. These situations occur because tank-style water heaters have what’s known as a ‘recovery rate,’ which refers to the amount of hot water the water heater can provide in a given period of time. The more you depend on hot water in your home, the higher the recovery rate you’ll need.

Pros of Storage Tank Water Heaters

  • Significantly lower upfront cost
  • Easy, low cost repairs
  • Ideal for larger homes

Cons of Storage Tank Water Heaters

  • Can only supply a limited amount of hot water in a given period of time
  • Slightly higher utility bills
  • Take up a lot of space
  • Less energy efficient
  • Shorter lifespan

Tankless Water Heaters

Although tankless water heaters are known for being pretty expensive upfront, they provide hot water pretty much on-demand – which makes sense considering they are also called ‘on-demand water heaters.’ These water heaters are outfitted with high-powered burners that heat water quickly as it runs through a heat exchanger and directly to your faucets and fixtures. As the name suggests, tankless water heaters do not utilize a tank for storage.

Tankless water heaters are between 24 and 34 percent more energy efficient than traditional storage tank water heaters. This means that they can save you quite a bit on your utility bills, and if you have a gas-fired model you can expect over $100 in annual savings. Though, the drawback to these water heaters is that they provide a limited amount of hot water per minute but the newest models can deliver up to 9.8 gallons of water per minute simultaneously!

Pros of Tankless Water Heaters

  • More energy efficient
  • On-demand hot water
  • Saves money over time
  • Take up less space

Cons of Tankless Water Heaters

  • Higher upfront cost
  • Costly repairs and replacements
  • Only provide a limited amount of hot water per minute

How to Size Your Water Heater

There are a number of hot water heater sizes available and in order to find the ideal size, you need to understand your average water usage. To do this, consider the following key factors:

  • Water heater’s physical size. It’s important that you choose a water heater that will fit in the designated space in your home. If you’re tight on space, consider a tankless water heater.
  • Household size. How big is your home? Do you live alone or do you have several family members in your house? Both the size of the home and its occupants are often the most important factors when it comes to choosing the ideal size water heater.
  • Fuel source. Will the water heater use electricity, liquid propane, or natural gas to operate? Or, is the water heater going to be hooked up to your boiler? Knowing this will help narrow down your choices.

What Size Water Heater Do I Need?

With the aforementioned factors in mind, the easiest way to determine the size storage tank heater you need is to go based off the size of your household. Oftentimes, you can use the number of people in your house as a good baseline for the ideal tank capacity (in gallons) for your water heater:

Household SizeNecessary Tank Capacity
1 to 2 people23 to 36 gallons
2 to 4 people36 to 46 gallons
3 to 5 people46 to 46 gallons
5 or more peopleOver 56 gallons (add 10 gallons for each additional person)

What is First Hour Rating?

A water heater’s first hour rating (FHR) refers to how much hot water the tank can create in a single hour when fully heated. So, if a water heater has an FHR of 90 gallons, this means that it can provide up to 90 gallons of hot water in a single hour.

Ideally, you want a water heater with an FHR that either meets or exceeds the number of gallons of hot water needed for all the activities that will take place simultaneously at the busiest time during the day. Consider the numbers in the following table to help you figure out peak hour usage and your ideal FHR:

ActivityHot Water Usage
Washing hands (per person)2 gallons
Shaving3 gallons
Washing dishes (hand-washing)6 gallons
Washing hair (per person)6 gallons
Running dishwasher5 to 10 gallons per load
Showering or bathing (per person)20 gallons
Running washing machine25 to 40 gallons per load

What Size Water Heater Do I Need for a Jacuzzi Tub?

Ultimately, the size water heater that you need will depend on the specific size of your jacuzzi tub. Soaking tubs and freestanding tubs usually hold around 60 to 80 gallons of water. Whereas, corner or spa tubs can hold between 70 to 120 gallons of water. With this in mind, your water heater tank must be at least 2/3 the size of your jacuzzi tub.

So, if you jacuzzi tub holds 120 gallons, you need at least an 80-gallon water heater. If you plan on using more appliances, faucets, and fixtures at the same time, you’ll need a water heater tank that’s even bigger.

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What About Tankless Water Heaters?

If you choose to opt for a tankless water heater instead – whether it’s for the improved energy efficiency, smaller size, or on-demand hot water – your shopping experience will be slightly different. Since tankless water heaters do not have a tank for storing water, you don’t need to concern yourself with capacity size. Instead, you must consider two key factors: flow rate and temperature rise.

Flow rate is measured in gallons per minute (GPM). To find out the size tankless water heater you need, determine the maximum number of appliances you want to run at the same time and their flow rate, then add up these rates. For temperature rise, you must subtract the incoming water temperature from the preferred output temperature.

Unless you know the incoming water temperature, you can assume that it’s 50 degrees Fahrenheit. Though, if you live in a warmer climate, it’ll be much higher. In most cases, you want the output water temperature to be between 105 and 115 degrees. This means that you’ll need a tankless water heater that produces a temperature rise of 55 degrees.

So, with these two factors in mind, the following table provides a good reference point for figuring out your home’s total simultaneous water needs:

FixtureAverage Flow Rate (GPM)Average Temperature
Sink1.5 GPM110°F
Dishwasher1.5 GPM110°F
Washing Machine2.0 GPM120°F
Shower2.5 to 3.0 GPM104°F
Tub4.0 GPM102°F

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Jessica Stone
Jessica Stone

Jessica considers herself a home improvement and design enthusiast. She grew up surrounded by constant home improvement projects and owes most of what she knows to helping her dad renovate her childhood home. Being a Los Angeles resident, Jessica spends a lot of her time looking for her next DIY project and sharing her love for home design.

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