What Size Tankless Water Heater Do You Need for a Family of 4?

Calculate the size tankless water heater you need for your family. Use our family of 4 calculator.

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If you have a family of four, you’ll need a tankless water heater that can provide at least 4 gallons of hot water per minute. Depending on your region, climate, and household habits, you might need a higher or lower flow rate. For example, if you live in a warm climate and take short showers, you might be able to get by with a flow rate of 3.5 gallons per minute. However, if you live in a cold climate or have longer showers, you might need a flow rate of 6 gallons per minute.

The Benefits of Tankless Water Heaters

Tankless water heaters have become increasingly popular in recent years, and for good reason. They are much more energy-efficient than traditional tank water heaters, and they can save you a significant amount of money on your energy bill. But what size tankless water heater do you need for a family of four?

There are a few things to consider when choosing a tankless water heater. First, you need to decide how much hot water your family will use on a daily basis. A family of four will use more hot water than a single person or couple, so you’ll need a larger unit. Secondly, you need to consider the climate in your area. If you live in an area with mild winters, you’ll probably be able to get away with a smaller unit. But if you live in an area with very cold winters, you’ll need a larger unit to make sure your family has enough hot water.

Once you’ve considered these factors, you can start looking at specific models. There are many different brands and types of tankless water heaters on the market, so it’s important to do your research before making a purchase. You should also consult with a professional to make sure you’re getting the right size unit for your needs.

Sizing a Tankless Water Heater

When you have a family of four, you need to make sure that you have a tankless water heater that can provide enough hot water for everyone.tankless water heaters are a great option for families because they are more energy efficient than traditional water heaters. They also take up less space, which is a plus if you have a smaller home.

Factors to Consider

When sizing a tankless water heater, there are 4 main factors you need to keep in mind:
-Peak hot water demand (in gallons per minute)
-Flow rate of incoming water (in gallons per minute)
-Temperature rise required
-Fuel type

BTUs and Gallons Per Minute

Tankless water heaters providing hot water on demand, meaning they heat water only when you need it. This saves energy and costs since the tankless system isn’t continuously running to maintain water temperature in an unused tank. When selecting a tankless system, you must determine the maximum flow rate and temperature rise you’ll need to accommodate your family’s peak hot water demands.

To calculate the maximum flow rate needed, consider how many devices will be running at the same time and concurrently draw hot water. For example, if you have a dishwasher and washing machine running at the same time, that would be two devices. If you also have three people taking showers, that would be six devices running concurrently. Consequently, you would need a tankless system that could provide at least six gallons per minute (GPM) to keep up with demand.

As for temperature rise, this is simply how much hotter the outlet water temperature needs to be than the coldest source of incoming water (typically 60°F). Most people are comfortable with an outlet temperature of 120°F. Use this formula to determine the required BTU input:
(BTU/hr) = 4 x GPM x Delta T
For our example of six GPM with a desired 120°F output temperature:
(BTU/hr) = 4 x 6 x 60
= 1440 BTUs/hr


In conclusion, you will need at least a 36,000 BTU tankless water heater to supply hot water for a family of four. This is based on the average hot water usage of a family of four, which is around 12 gallons per day. If you have a high hot water usage, you may need a larger tankless water heater. You should also consider the climate when selecting a tankless water heater. In colder climates, you will need a larger tankless water heater to maintain a consistent supply of hot water.