What Size Hot Water Heater Should You Choose?

When you’re looking for a new hot water heater the first question you’ll probably ask is what size hot water heater you should get. With a variety of sizes and types it can be confusing to know which one works best for your home and family. In this article we’ll quickly break down how to find the proper hot water heater, as well as the different options to keep in mind.

Quick and Easy Method

If you’re looking for the quickest method to figure out your size use the below guidelines based on the number of people in your household.

1-2 people: 30-40 gallons
2-3 people: 40-50 gallons
3-4 people: 50-60 gallons
5+ people: 60-80 gallons

This is just an estimate, but is usually fairly accurate to what most people will need. If you’re heavy water users you may want to go up a size to prevent running out of hot water.

The More Accurate Method

If you’re looking for a more accurate method of calculating your hot water needs follow these steps.

1. Determine Peak Hour Usage

First, you want to figure out when your household uses the most water. This is what is known as peak hour usage, and should be the maximum amount of water you’ll use.

With that in mind, you can use the following guidelines to get a rough estimate of how many gallons per water you’re using during the busiest time of the day. All the numbers below are a rough estimate of the gallons an activity uses and should be multiplied by the number of times that activity takes place in an hour.

For example, showing uses about 15 gallons of water, so if two people plan to shower in the same hour you should estimate 15 x 2 = 30 gallons of water.

Showering: 15 gallons
Shaving: 2 gallons (per minute)
Washing dishes or hands: 2 gallons (per minute)
Dishwasher: 10 gallons
Clothes Washer: 14- 20 gallons (depending on efficiency)

Add up all the water used during your busiest hour and this will give your peak hour usage number.

2. Look at First Hour Rating (FHR)

With the above number in mind, you’ll want to look for a tank that has a First Hour Rating (FHR) within a few gallons of your usage. The FHR is the amount of hot water a tank can provide in an hour starting from a full tank.

This number is the best indicator of how much hot water you can expect from your hot water heater while being used consistently. The higher this number is, the more hot water your heater can provide per hour.

There’s always a trade off though, and larger tanks usually cost more. That’s why it’s a good idea to get as close as possible as going far over your need is going to be an unnecessary expense.

What About Tankless Heaters?

Your other option is to go with a tankless heater. Tankless heaters don’t store heated water but instead heat it on demand as you use it. This means they’re smaller and more efficient than tank heaters, but are a bit more expensive. Depending on your needs though, they can make up for this higher initial cost by being more energy efficient in the long term.

When looking at tankless heaters you want to keep in mind the flow rate along with the required rise in temperature that needs to take place.

For flow rate you want to do a similar calculation as above. Flow rate for tankless heaters is generally listed in gallons per minute, here’s an example of some common activities and how many gallons they use per minute.

Showering: 2 gallons per minute
Dishwasher: 1 gallon per minute
Washing your hands: 1 gallon per minute
Washing machine: 1-3 gallons per minute

Start by determining what your max usage is per minute during the busiest time of the day.

Once you do that, you also need to know how much the water needs to be heated. To find this, subtract the temperature of watering entering your house from the desired temperature. You can get the starting temperature by using a thermometer with some tap water, or check out this chart which lists averages by region.

Once you have both of these numbers you can consult the manufacturer documentation to find out which heaters match your needs. This will generally be in the form of a chart that lists the maximum flow rate for a given starting temperature.