Quality water heaters are non-negotiable for many homeowners, even those that aren’t a fan of hot showers. Unfortunately, most people aren’t aware of how critical the right size is or why it even matters when choosing a water heater. Luckily, there are ways to easily tell what size water heater you need so that you can make an overall more informed buying decision.
Know the Averages
Averages are going to play a significant role when it comes to performing any water heater calculation; if you don’t need an exact measurement, there are guidelines you can follow. First, you need to determine how many people are in the household, as this number will correspond with how many gallons your tank needs to hold. Once you’ve determined how many people live in the home and will be using hot water, you can follow this quick guide:
- One to two people require 30–40 gallons
- Two to three people require 40–50 gallons
- Three to four people require 50–60 gallons
- Five people or more require 60–80 gallons
While these estimates are helpful, they leave a lot of room for error, especially if there are more than five people in the home.
Calculate Peak Hour Demand
In truth, oversizing and under-sizing are some of the most common mistakes people make when buying a residential water heater. Oversize, and you’ll be wasting more energy keeping all that water hot. Undersize, and you’ll run out of hot water too quickly. In order to tell what size water heater you need, you’ll need to calculate peak hour demand. Peak hour demand is the point in time when you’ll be using the maximum amount of water if all appliances are running at the same hour. Here is where averages will come back into play.
First, you’ll need to take inventory of all the appliances and activities in your home that need hot water, such as showering, shaving, running washing machines, doing dishes by hand, or using the dishwasher. Each of these activities has an average amount of hot water gallons per usage. For example, a shower uses up about 20 gallons of hot water, while an automatic dishwasher uses 14, and handwashing takes 4. Then, you’ll need to multiply the gallons used by how many times these appliances could be used in that hour at the same time. For example:
Shower (20 gallons) x 2= 40 gallons
Dishwasher (14 gallons) x 1= 14 gallons
Handwashing (4 gallons) x 5= 20 gallons
Then, you’ll add up the resulting gallons to get your peak hour demand, which would be 74 gallons used in an hour at maximum in our example scenario.
Consider the Water Heater’s FHR
Calculating your peak hour demand will help determine what your water heater’s first-hour rating should be (FHR). This number will tell you how much hot water a tank can give you per hour. You can find this number on the yellow Energy Guide sticker on the side of the heater. This number should closely match your peak-hour demand. In our above example, our calculation showed 74 gallons of hot water, which means the tank’s FHR should be at least 74.
If you’ve found the right FHR match, congratulations! You’ve found the perfect-sized water heater to meet your home’s needs!