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Residential Water Heater Sizing
With over 80 years of delivering innovative water heating solutions, A. O. Smith is proud to be a leading manufacturer of residential water heaters. With a wide variety of sizes, features and capacities, our water heaters are designed to provide the optimal solution for your lifestyle or geographic location.
Understanding Your Hot Water Needs
Choosing the right size water heater starts with understanding how your household uses hot water, from shower habits to appliance use and how often those overlap.
Key factors include storage capacity versus recovery rate, available installation space, and whether a tank or tankless system fits your daily routine. Tank water heaters store a ready supply and work well for filling large bathtubs or running multiple showers at once, while tankless models heat water on demand and are a good fit for back-to-back showers in homes with limited space.
No water heater delivers truly instant hot water on its own, as delivery speed also depends on the unit's features, its distance from fixtures, and local climate. A. O. Smith's XPERT Water Heater Selector can help homeowners find the right fit based on their specific needs.
Determining Your Priorities
Choosing the right size of water heater also depends on your personal priorities.
Consider the sliding scale between water heater storage capacity vs. water heater recovery rate. This is the balance between how much water your water heater can store and how quickly it can reheat the water in its tank. The right water heater for you depends on what is most important to you.
Tank water heaters offer storage capacity, which is great for large uses like filling a large bathtub or multiple showers at the same time, but it will take time to reheat before you have a full tank of hot water again. Alternatively, tankless water heaters generate hot water on demand so they are great for sustained hot water use like back-to-back-to-back showers, but you may be limited on how many fixtures you can use simultaneously. Learn more about tank and tankless water heaters.
Determining these priorities helps you to not only determine water heater size, but also the overall type of water heater that will be best for you.
Your Space Requirements
After understanding your hot water needs and thinking through your priorities, consider the amount of space you have available for a water heater. Large storage tank water heaters require a large area for installation and may not be ideal for small spaces. They are often installed in basements, closets, and places away from general living.
A tankless water heater is a great solution for those with minimal space as they are compact and can be installed in areas of your home as small as a closet. When making a purchasing decision, it is important to consider where the water heater needs to be installed and how much room is available.
"Instant" Hot Water
No matter the brand or type (tank or tankless), a water heater alone will not deliver instant hot water to a shower, faucet or appliance. The correct features, capabilities, location and technology must be in place to enable the immediate delivery of hot water. Below are a few factors that may impact the delivery time for hot water to reach your fixture.
Capabilities: Certain product features help facilitate instant hot water delivery. For example, a built-in recirculation pump paired with a recirculating piping system returns unused hot water back to the water heater for reheating instead of going down the drain.
Proximity: If you do not have a recirculation pump with the necessary piping system installed, the proximity of the water heater to the water fixture will impact how quickly the fixture receives hot water. Hot water will be delivered faster when the water heater is closer to the fixture because the length of piping in between the two is shorter.
Temperature: The temperature of the piping between the water heater and the location of the water fixture is another factor that may impact hot water delivery. Climate, weather, seasonal changes and the path of the hot water pipe can all have an impact. For example, during a northern United States winter, 40 feet of piping in a crawl space without recirculation assistance will take longer to deliver hot water than 40 feet of piping in an attic during a southern United States summer.
Frequently Asked Questions
Start by thinking about your busiest hot water hour, usually the morning when showers, laundry, and dishes overlap. Add up how much hot water your household uses during that window, then look for a water heater with a first hour rating that meets or slightly exceeds that number. The first hour rating tells you how much hot water a tank can deliver during the first hour of heavy use starting with a full tank. Available space and whether a tank or tankless system fits your routine also factor in. A. O. Smith's XPERT Residential Water Heater Selector walks you through the process and gives personalized recommendations based on your habits and local climate.
Bedroom count is not the best way to size a water heater since a 3 bedroom home could have two people or five. What matters more is how many people live there, how long showers run, whether they happen back to back, and how often hot water appliances overlap. As a general starting point, 40 gallons works well for one to two people with average usage. Larger households will likely need more capacity. A. O. Smith's XPERT Residential Water Heater Selector gives recommendations based on your actual usage patterns.
For many families of four, 50 gallons is a comfortable fit, but it depends on habits. Families who stagger showers and spread out appliance use throughout the day typically do well. If showers overlap or multiple hot water appliances run at the same time, you may need more capacity. A. O. Smith's XPERT Residential Water Heater Selector can help you find the right size based on how your family actually uses hot water.
It depends on shower length and whether showers happen one after another or at the same time. A standard shower uses roughly 20 gallons, so a 50 gallon tank can generally support two to three consecutive showers before running low. The first hour rating matters too, since the unit keeps heating water as it is used, extending total output beyond stored capacity. Spacing out showers and using standard flow fixtures helps a 50 gallon unit go further. Use A. O. Smith's XPERT Residential Water Heater Selector for a personalized recommendation.
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Why A. O. Smith?
A. O. Smith is a leading manufacturer of both residential and commercial water heating technologies, including the #1 most specified commercial water heater.
For more than 145 years, we’ve developed state-of-the art products that push new boundaries and improve the lives of our customers.
We combine cutting-edge technology with committed people who take pride in providing the very best support for our customers.
Our products are put through rigorous quality and endurance testing so no matter where hot water is needed, A. O. Smith can provide a solution you can count on.