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Tankless Water Heaters: How to Pick the Perfect Size For Your Florida Home

Installing a tankless water heater is great if you want endless hot water and lower energy bills.

Installing a tankless water heater is great if you want endless hot water and lower energy bills.

But if your tankless water heater isn’t the right size it won’t be able to supply the amount of hot water you’ll need--leaving you with serious buyer’s remorse

Tankless water heaters are sized by the maximum temperature rise possible at a given flow rate. So that means you need to:

  • Find the flow rate needed
  • Determine temperature rise needed

Don’t worry, we’ll define all of these terms for you in this article.

Finding the flow rate

Flow rate is the maximum amount of hot water a tankless water heater can provide at a given time. It’s is measured in gallons per minute (gpm).

To find the flow rate your tankless water heaters needs, calculate how much hot water you typically use at one time.

To do this, add the flow rates of the appliances in your home you use simultaneously. Here are the flow rates for major water-using appliances and fixtures:

  • Bathroom faucet: 0.5-1.5 gpm
  • Low flow kitchen faucet: 3.0-7.0 gpm
  • Shower 1.0-2.0 gpm
  • Dishwasher: 1.0-2.5 gpm
  • Clothes Washer: 1.5-3.0 gpm

For example: If you’re usually washing clothes at night (as some do to avoid peak hour rates) and someone also showers at night, then you’ll want a tankless water heater that has a flow rate of 2.5-5 gpm.

So, as you’re shopping for a tankless hot water heater, you’ll see something like “4 gmp” next to the name of the tankless water heaters. That means it can provide a maximum of 4 gallons of hot water per minute.

Determining temperature rise

Knowing the maximum flow rate isn’t the whole story. Flow rate descriptions for a tankless water heater are for the lowest minimum temperature rise needed.

Temperature rise is the difference between the temperature of the hot water exiting the tankless water heater and the cold water entering it.

As a formula it looks like this:

Desired hot water temperature - Incoming ground water temperature = Temperature rise

Understanding temperature rise is important because it’s inversely related to the flow rate a tankless water heater can provide. So if the temperature rise needed is low, then the tankless water heater’s flow rate will be higher to it’s maximum.

That makes sense, right? If you need less hot water, the tankless water heater has more time to heat the water coming through it.

Calculating temperature rise for a typical south Florida homeowner looks like this:

120 ºF - 72ºF = 48ºF

Lucky for you, Florida’s water is warmer and therefore the temperature rise needed is much lower, meaning a tankless water heater can still provide hot water at greater flow rates.

So, as you’re shopping for a tankless hot water heater don’t look at just the flow rate. Look at the flow rate a tankless water heater can provide at a specific temperature rise (particularly, Florida’s).

Getting help

Need help finding a tankless water heater that’s sized for your home? Ask one of Plumbing Today’s experts for help.

Plumbing Today provides award-winning plumbing service to Sarasota, Florida and the surrounding areas like Bradenton, Tampa and Port Charlotte.