It’s time to replace your water heater, but what size should you get? Replacing like-for-like isn’t always the best option because your household’s needs can change. A water heater that’s too small can’t keep up with demand, and one that’s too big wastes energy, ratcheting up your energy bill unnecessarily. Use this guide to figure out the tank size that will best suit your needs. Or, if you’d prefer some personal help making your decision, reach out to us at Benjamin Franklin Plumbing. We’d love to assist!
Water Heaters with Tanks
Water heaters with insulated storage tanks are the most common type in U.S. homes. They come in a range of heights and widths to fit your space and a variety of gallon capacities to meet your household’s water-use needs. A great starting point is to choose a gallon size based on the number of people in your home.
In general, one to two people require a capacity of 23 to 36 gallons, two to four need 36 to 46 gallons, and three to five residents need 46 to 56 gallons. For households with five people, aim for a 56-gallon tank, and add 10 gallons for each extra person.
Now that you know how to estimate the size of the tank, look at an equally important factor — the first-hour rating. When you get this rating right, you won’t have to worry about running out of hot water during peak usage times at home.
Every new storage-tank water heater has a label that provides its first-hour rating. The label shows something like “Capacity: (first-hour rating) 80 gallons.” This rating tells you the number of gallons a hot water tank can supply in one hour, starting from a fully heated tank. That number is different from the tank’s physical capacity. For example, a 50-gallon tank could have a first-hour rating of 75 gallons per hour. So, if you are comparing two water tanks with the same gallon capacity, the one with the higher first-hour rating will allow you to use more hot water before it runs out.
To select the optimal first-hour rating, make a quick list of how much water each person in your home typically uses during peak times, and add those up. Here are some average gallons of water people use per task:
- Filling a bathtub: 36 gallons
- Taking an 8-minute shower: 16 to 40 gallons (depending on the water efficiency of your showerhead)
- Brushing teeth: 2 to 4 gallons
- Shaving: 3 gallons
- Handwashing dishes: 9 to 27 gallons
- Machine-washing clothes: 25 to 40 gallons per load
The total number of gallons you come up with is your ideal first-hour rating. If you’d like some expert help selecting the correct size tank, we’re here to help at Benjamin Franklin Plumbing.
Tankless Water Heaters
An alternative to traditional tank water heaters, tankless models heat up water on demand. By figuring out two specific numbers, you can choose the right size tankless heater so you never run out of hot water when you need it. Those numbers are:
- Flow rate in gallons per minute (GPM): How much hot water you routinely need to use
- Temperature rise: The difference between how cold the water is when it enters your house and how hot you want it to be.
Again, list all the fixtures and appliances in your home that use hot water — showers, sinks, dishwashers, washing machines, and so on — and think about how many of these are used during the busiest time in your house for hot water use. Add up the estimated gallons per minute (GPM) that each fixture uses. For example:
- Shower: 1.5 to 3 GPM
- Bathroom sink: 0.5 to 1.5 GPM
- Kitchen sink: 1 to 1.5 GPM
- Dishwasher: 1 to 2.5 GPM
- Washing machine: 1.5 to 3 GPM
So, if your spouse typically takes a shower, which uses 3 GPM, while you wash dishes using 1 GPM, that’s a total of 4 GPM.
To make sure your water heats up to the right temperature, you’ll also need to calculate something called temperature rise. All this means is subtracting the current temperature of your incoming cold water from how hot you want your water to be. If your incoming water is 50°F and you want it heated to 120°F, you’ll need a temperature rise of 70°F. Choose a tankless water heater to meet your peak GPM demand at the target temperature rise.
Choosing the Right Size Water Heater
Choosing the right size water heater can significantly impact your comfort and your energy bills. If you’re not sure where to start or feeling overwhelmed by the numbers, don’t hesitate to contact us at Benjamin Franklin Plumbing. We’re just a call away and happy to help you find the perfect water heater size for your home!