Installing the right water heater in your home plays a contributing factor to yours and your family's comfort – ensuring there is enough hot water for each person and the various daily tasks that need to be performed. On average, the cost of heating water accounts for 14% – 18% of your utility bill, making it the second largest expense (after electricity), so you'll want to get the right size for your needs. Below is a breakdown of water heater sizes so you can choose the appropriate one for your household to both meet your family's demands as well as save you money and energy.

What Are the Different Water Heater Sizes?

We have four different water heater sizes available for you to choose from:

But before you can select your size, you need to consider what type of tank you are looking for. There are two types to choose from.

Tank Heaters: One of the most common household water heaters available is the storage or tank water heater. They are relatively low-cost to run and can use electricity, propane, or natural gas. Tank water heaters store around 20 to 80 gallons of hot water ready to be used at any time. The heated water comes from the top of the tank and flows to the faucet, while the rest of the cold water remains behind to ensure there is always water for the tank to heat.

Tankless Water Heater: Tankless water heaters don't have storage, meaning the water travels straight through a heat exchanger (that uses electricity or gas) to instantly deliver hot water where needed. These generally provide between 7 to 12 gallons of hot water per minute and are much smaller than their storage counterparts. For this reason, tankless water heaters must be selected on their flow rate (described below) and not the tank capacity. It also means you likely can't heat multiple appliances (washing machine, shower, dishwasher) at the same time, meaning you may require more than one tankless heater to adequately provide hot water.

To learn more about water heater types, read Everything You Need to Know About Types of Water Heaters as well as Types of Water Heaters: Tank vs. Tankless. Once you've selected the type of water heater you intend to use, you can move onto picking the correct size for your household.

Calculating Water Heater Sizes

Storage Tank Water Heaters

The size of your family will greatly affect what size water heater you should get. If you opt for a storage tank water heater, you can buy your water heater on these general estimates:

1 – 2 people: At least a 30-gallon capacity.
2 – 3 people: At least a 40-gallon tank.
3 – 4 people: At least a 50-gallon electric or 40-gallon gas water heater.
For a family of 5 or more: An 80-gallon electric or 50-gallon gas water heater

The more your family uses hot water on a regular basis, the more capacity you will need. For example, if four people each take a 10 minute shower all within one hour, these will use 40 gallons of hot water. For a tank of the same size, this will mean there is no more hot water for that hour until the water heater heats up more. Anyone who showers longer than that will use up more hot water, so it is imperative to take your family's daily routine into consideration when selecting your water heater size.

Family Size: 1 – 2 members
Demand: High or Regular/Low
Gallon Capacity: 40 – 50 gallons or 30 gallons

Family Size: 2 – 3 members
Demand: High or Regular/Low
Gallon Capacity: 40 – 50 gallons or 40 gallons

Family Size: 3 – 4 members
Demand: High or Regular/Low
Gallon Capacity: 50 – 75 gallons or 40 gallons

Family Size: 5+ members
Demand: High or Regular/Low
Gallon Capacity: 75 gallons or 50 gallons

First-Hour Rating

Another method you can use to calculate the water heater size is by using the first-hour rating which tells you the amount of hot water your water heater can deliver in one hour.

Begin by choosing the hour of the day your household uses the most water.
Use the activity table to find the amount of hot water you use for each activity during that hour.
Add up all quantities for that hour and that total will equal your first-hour rating.
It's a good idea to select a water heater with a first-hour rating close to the total amount of hot water you use during the hour you have chosen. The first-hour rating also includes the recovery rate (a combo of the amount of water stored in the heater and how quickly the heater can heat the cold water to the desired temperature).

Activity/Appliance: Washing Machine
Hot Water Used: 25 – 40 gallons per load

Activity/Appliance: Dishwasher
Hot Water Used: 5 – 10 gallons per load

Activity/Appliance: Hand-Washing Dishes
Hot Water Used: 3 – 4 gallons

Activity/Appliance: Bathing
Hot Water Used: 15 – 25 gallons

Activity/Appliance: Showering
Hot Water Used: 3 gallons per minute

Activity/Appliance: Bathing an Infant
Hot Water Used: 2 gallons

Activity/Appliance: Shaving
Hot Water Used: 2 – 3 1/2 gallons

Activity/Appliance: Shampooing
Hot Water Used: 5 gallons

Activity/Appliance: Hand Washing
Hot Water Used: 1 – 2 gallons

Activity/Appliance: House Cleaning
Hot Water Used: 5 – 12 gallons

Activity/Appliance: Food Preparation
Hot Water Used: 3 – 6 gallons

Tankless Water Heater Sizes

If you are considering a tankless water heater, your calculations will be a little different. Since these tanks don't store water, they use gallons per minute (GPM) for sizing, so before you can figure out what heater you need, you need to calculate the following measurements:.

1. Peak Demand Hour: Find out how many water fixtures you use during your peak hour of demand (this includes faucets, showers, and appliances).

2. Flow Rate: To calculate the flow rate (GPM) of each fixture, first look in the manufacturer's guide for your fixtures but if you don't have thins, then put a bowl or pot under the spigot and let it run for one minute. Measure that amount of water and multiply it by 60 to get the flow rate for that fixture.

3. Maximum GPM: Take the flow rates of all the fixtures you use during the peak hour and add them up to get your maximum GPM.

4. Temperature Rise: To get the temperature rise you can run a cold water faucet and take its temperature with a thermometer. Then subtract this number from 120 (the typical temperature in Fahrenheit needed for most hot water uses).

As an example – if your incoming water temperature is 50°F and 100°F is the outgoing temperature, you would want a tankless water heater with a temperature rise of 50 degrees. Based on a 50°F groundwater average, here are the tankless water heater sizes you would need based on your usage.

• For one to two fixtures at a time, you'll need at least 3.5 GPM (gallons per minute).
• Two to three fixtures at a time, you'll need at least 5 GPM.
• Three to four fixtures at a time, you'll need at least 7 GPM.
• If you intended to use five or more fixtures at once, you may need multiple tankless units.

Once you have the max GPM and temperature rise, you can compare the different tankless models.

Whether you are replacing the one you have or are installing a brand new heater, hopefully this information on water heater sizes can help you choose the appropriate one for your household and its water needs.

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