Going Tankless in Tampa? What Size do You Need?

When it comes to tankless water heaters, size matters. If you install a unit that’s too small, you won’t have enough hot water to meet demand. On the other hand, an oversized unit will cost more to purchase and operate than necessary, negating one of the biggest benefits of tankless water heaters—energy efficiency!

In short, the tankless water heater size must be just right to meet your expectations. Consider the two factors that go into sizing a tankless unit so you know what to install in your home.



The flow rate is how much hot water the tankless unit can produce, expressed in gallons per minute (gpm). You want the unit you install to provide a high enough flow rate to meet your needs. Keep in mind that tankless water heaters will typically restrict your family to one or two hot water activities at a time, depending on the size you install.

Examples of efficient, low-flow hot water plumbing fixtures include:

  • Bathroom sink faucet – 1.0 gpm
  • Showerhead – 2.5 gpm
  • Tub faucet – 4.0 gpm
  • Kitchen faucet – 1.5 gpm
  • Dishwasher – 1.5 gpm
  • Washing machine – 2.0 gpm

Now, determine how many of these hot water fixtures you expect to use during peak times. For example, if you have two bathrooms and want two people to be able to shower at the same time every morning, you’ll need a flow rate of around 5 gpm, depending on the precise flow of your showerheads.


Knowing the flow rate you want is a good place to start, but it’s not enough. You must also consider the temperature of the water when it goes in and how hot it should be when it comes out. This is known as the temperature rise. Seasonal shifts change the incoming water temperature, but for the purposes of sizing a tankless water heater, you just need to know the average groundwater temperature in your region.

In the Tampa Bay region, the temperature of the ground water does fluctuate from 85°F August and down to 62°F in February. The temperature you want at the tap ranges from 102 degrees for the bathtub and shower to 120 degrees for the dishwasher and washing machine. Starting with 62-degree water (in February), this means you need a tankless unit capable of delivering a temperature rise of 40 to 58 degrees.


As you shop for tankless water heaters, you’ll see that their sizes are listed as a combination of flow rate and temperature rise. It’s important that you consider how much use your new tankless water heater is going to get. You do not want to make the mistake of buying a unit that is too small for your daily consumption.


The water heater experts at Cass Plumbing can help you determine the proper tankless water heater size for your family’s needs. We perform careful calculations to help you achieve a balance between purchase price, performance, and energy efficiency.

If you move forward with the tankless water heater installation, rest assured that the Tampa plumbing professionals at Cass Plumbing are highly qualified for the job. We are fully trained, licensed, certified, and bonded, and our plumbers are background-checked and drug-tested for your peace of mind. We have 2o years of experience providing excellent plumbing service to our residential and commercial customers throughout the Tampa Bay region.

When you need a good plumber in Tampa, for your tankless water heater needs give us a call. Cass Plumbing has thousands of 5 star reviews online, is ranked #1 by Best Plumbers for the Tampa Bay region and has earned an A+ rating by the Tampa Bay Better Business Bureau. Get in touch today with us today at (813) 265-9200.