What Size of Hot Water Tank Do I Need?

Is your water heater old or inefficient? Has your family grown to the point that your need for hot water now outweighs what your tank provides? These are signs that it's time for a new water heater. 

But before you decide, let the experts at Premier Systems educate you on the basics of determining water heater sizes. At Bozeman, Montana's reliable water heater service, we’re here to advise you as you choose your new water heater. 

There are several types of water heaters available, so the first step is figuring out which one meets the demands of your household. The key to a water heater that operates efficiently while also providing the right amount of hot water? Size.

How To Decide Which Size Water Heater Is Right for You

Figuring out the size of hot water tank is important, and the answer involves some research and a little bit of math. Below, we offer some guidance for selecting the perfect type and size of water heater for your home. 

Choosing a Tank Storage Water Heater With a Heat Pump

The key to choosing the correct size of storage for a water heater is determining the first-hour rating (FHR). The FHR also depends on tank capacity, whether the source of heat is gas or electric, and the size of the gas burner or electric element. First-hour ratings show you the number of gallons of hot water your water heater delivers per hour, as measured when the water storage tank is full. 

The other thing to consider is the "peak hour demand" in your home. This refers to the time of day when hot water use is highest. We've listed some of the most common peak hour activities per person below, giving you a better idea of how to estimate your peak hour demand: 

• Showers - 20 gallons
• Hand washing - 2 gallons
• Food Preparation - 6 gallons
• Running the dishwasher - 14 gallons
• Running the washing machine - 30 gallons

When sizing a water heater, a good rule of thumb is to select one with an FHR that matches or exceeds your peak hour demand, ensuring available hot water for everyone. In general, you will need a storage tank with a capacity that fits the size of your family. A good way to figure that number out is to assume 23-36 gallons for a two-person household and an additional 10 gallons for every additional person. 

Choosing a Tankless Water Heater

The best way to determine the correct size of a tankless (or on-demand) water heater, you need to measure two things: temperature rise and flow rate.

Flow Rate

To estimate flow rate, start with a list of hot water appliances you would use at one time—for example, a shower and a kitchen sink. Determine their individual flow rates by measuring the amount of water that each appliance uses per minute. You can easily figure out flow rate by holding a container under the water flow for one minute and measuring the volume of water each appliance uses. Add up the totals of the two appliances to see the gallons per minute. If the shower output is 2.5 gallons per minute and the sink output is .75 gallons per minute, you require a water heater with a flow rate of 3.25 gallons per minute. 

Temperature Rise

Temperature rise refers to the number of degrees incoming water must increase to reach the desired hot water temperature. To estimate temperature rise, you subtract the incoming water temperature from your desired output temperature. For example, if your incoming water is 55 degrees, and your desired temperature is 120 degrees, the temperature rise is 65 degrees. If you don't know the temperature of your incoming water, hold your thermometer under a cold-water faucet and go from there. 

Tankless water heaters have the ability to heat your incoming water starting from a variety of temperatures. The speed at which the water heats up depends on whether the hot water heater is gas-powered or electric. Gas-powered water heaters tend to heat water faster. 

Choosing a Solar Water Heater

Solar water heaters involve a few more critical and complex calculations when choosing the right size for your needs. Choosing the correct size for your solar water heater relies primarily on determining the amount of collector area and storage tank volume necessary to meet at least 90% of your hot water demands in the summer. 

Collector Area

Collector area refers to the size of the solar "collector" facing the sun. General guidelines for a solar water heater require roughly 20 square feet of collector area per person for the first two people in the household. You then add between 8-14 square feet per additional person. The range in collector area for additional people depends on the region where you live and the amount of sun; sunny climates need less area, while northern states require more.

Storage Volume

Storage tank size also depends on the number of people in the home, with a smaller tank (50-60 gallons) easily serving one to two people, a medium (80 gallons) for three to four, and a larger tank for any more than four residents. 

The size of the collector influences the size of the storage tank as well. Solar water heater experts recommend a storage tank that holds 1.5 or two gallons of water per square foot of collector area. This prevents the water heater system from overheating at times of low demand. 

If those calculations sound complicated, don't worry: our highly trained professionals utilize worksheets and software to establish your solar water heater system requirements.   

Water Heater Services at Premier Systems in Bozeman, MT

If a new water heater is your next big purchase, the essential question is, "What size of hot water tank do I need?" Let our licensed professionals at Premier Systems assist you as you determine the right size water heater for your household's needs. Contact us today to schedule a consultation. We're here to educate you on how long water heaters last, proper maintenance, and install or repair any appliances for you.