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What Size Water Heater Do You Need?

When you’re choosing a water heater, there are a lot of things to think of, but the first thing you should decide is what size do you need? Do you need something smaller like a 40 gallon water heater, or something larger?

A properly sized water heater will meet your household's hot water needs while operating more efficiently. Sounds easy, right? Well, it’s a bit more complicated than that. Each type of water heater has different sizes and demands available. There are:

  • Tankless or demand-type water heaters

  • Solar water heating system

  • Storage Water heaters (tanks)

Sizing Tankless Or On-Demand- Water Heaters

To size a tankless or an on-demand water heater, you’ll first need to know what flow rate and max temperature you’ll need while it’s in use. That can be tricky, so first ask yourself what you’re doing it for. Is it for the whole house, or a single bathroom?

Once you’ve done that, the Department of Energy outlined the next steps to find the flow rate.

  1. List the number of hot water devices you expect to use simultaneously.

  2. Then, add up their flow rates (gallons per minute). This is the desired flow rate you'll want for the demand water heater.

  3. Let's say you expect to simultaneously run a hot water faucet with a flow rate of 0.75 gallons per minute and a shower head with a flow rate of 2.5 gallons per minute. The flow rate through the demand water heater would need to be at least 3.25 gallons per minute.

Finding the right temperature is a little bit easier. Most houses have a default water temperature of about 50 degrees Fahrenheit, which we can use here to determine your ideal heat rise. All you need to do is subtract 50 from your desired output temperature.

For example, let’s say you want your water to be heated up to 120 degrees. So subtract 50 from 120 and you’d get 70. That means you need a water heater that can produce a rise of 70 degrees.

Once you know that, it’s as simple as finding a unit that works for you with both the temperature and sizing requirements.

Sizing A Solar Water Heating System

Solar systems are a bit more complicated to size. We recommend talking with a professional to see if a solar-powered unit is right for you. However, here’s a gist of how to find one that’s right for you.

Sizing your solar water heating system basically involves determining the total collector area and the storage volume you'll need to meet 90%–100% of your household's hot water needs during the summer.

A small (50- to 60-gallon) storage tank is usually sufficient for one to two three people. A medium (80-gallon) storage tank works well for three to four people. A large tank is appropriate for four to six people.

Additional calculations involved in sizing your solar water heating system include evaluating your building site's solar resource and determining the proper orientation and tilt of the solar collector.

Sizing Water Heaters with Tanks

Water heaters with tanks, otherwise known as storage water heaters, are very common for residential homes. These are where the size really comes into play, as hot water is stored in the tank and is ready for use...until it’s not.

Fortunately, storage water heaters use easy to follow ratings. For a tank-style heater, you can estimate the necessary tank capacity (in gallons) based on the number of people in the house:

  • 1 or 2 people—23 to 36 gallons

  • 2 to 4 people—36 to 46 gallons

  • 3 to 5 people—46 to 56 gallons

  • 5 or more people—over 56 gallons (add 10 gallons per additional person)

If a larger tank won’t fit in the existing space, consider a tankless heater.

And if in doubt, give us a call. Our plumbers will help guide you to finding the right water heater for your home and family. We strive to exceed expectations by ensuring that all of your plumbing service needs are completed to the highest standards. We will provide you with a free consultation to explain all of your available options so that you can choose the scope or work that’s right for your home or business.

We are confident in our team, and know that you won't be disappointed, that's why we stand behind our 100% satisfaction guarantee on all of our work. Whether you need a water heater repair, water heater replacement, or new water heater installation, you can count on Better Choice Plumbing to do the job right the first time.

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