What Size Tankless Water Heater Do I Need?

Owning a home comes with a lot of responsibility. Making sure that your plumbing is built correctly is one of many responsibilities. You don’t want to have the wrong-sized or tankless water heater installed in our home. This could cause some problems with getting the proper amount of heated water flowing through your plumbing system. What size tankless water heater do I need? This depends on how many people live in the home and the climate that you live in.

Let’s take a look below at some more tankless water heater information.

What Are Some Factors To Consider?

Believe it or not, when looking to determine how big of a tankless water heater your home needs, there are a variety of factors to consider. Let’s take a look below at what those factors are.

  • Groundwater temperature
  • The number of people living in your home
  • The local climate
  • The size of your home in square footage
  • The number of appliances that you will need to run at one time

It is important to ensure that you meet the needs of your home. Selecting a tankless water heater that is too small for your home could be detrimental to your hot water needs. Consequently, installing one that is too big for your home, could end up driving up your energy bill costs.

Wall mounted tankless water heaters can be great space savers in a home.

How Do I Figure Out The Right Size For My Home?

The best way to determine which size tankless water heater is right for your home is by calculating the Flow Rate, gallons per minute or (GPM), and temperature pressure. Tankless water heaters list their max GPM Flow Rate and the required temperature rises. Determining the peak hot water flow for your home and the necessary water temperature rise as the water enters the home is key.

How To Calculate The Capacity Of A Tankless Water Heater?

Calculating the capacity of your tankless water heater is fairly simple. You just have to add and subtract various factors. Let’s take a look below at what’s involved.

  • Add them up – Add up the flow rates of all appliances that you will likely run simultaneously.
  • Use a chart – Collect the standard flow rates and the temperature rise that will need to occur.

Let’s take a look at some of the breakdowns.

Flow Rates Measured In Gallons Per Minute (GPM)

  • Sink faucet—1 GPM
  • Shower—2.5 GPM
  • Bathtub—3 GPM
  • Dishwasher—3 GPM
  • Clothes washer—3 GPM

Adding up your appliance Flow Rates allows you to now calculate the size of your tankless water heater needs. Take the temperature rise needs and use a groundwater temperatures map to calculate. For example, if you live in Florida, the Temperature Rise is going to be 35 degrees Fahrenheit. So, the tankless water heater size that is needed is a Flow Rate of 4 GPM at 35 degrees Fahrenheit.

If you are looking to run your washing machine and shower at the same time then you will want to find the right size tankless water heater. The incoming water temperature will need to be heated up to meet your hot water demands. Gas tankless water heaters will need to ensure the pilot light is lit as opposed to an electric tankless water heater that just requires power. The amount of hot water distributed throughout the house in a water-per-minute scenario is determined by the tankless unit.

Recommended Maintenance

Now that you know about sizing your tankless water heater, let’s take a look at some other areas. One of those is stopping a leaky pipe. This can be done by applying epoxy putty, using a pipe repair kit, and a patch and clamp.

Another area is the toilet. If you find that the toilet keeps running, it may be that the flapper needs to be replaced or the fill valve in the tank. It is important to find out what it is before your water bill is sky-high!

Lastly, you may need to adjust the water pressure in the sinks. You will do this by adjusting the water pressure regulator. This involves the water supply line, the pressure valve, and other steps.

Allowing the flow of water is key for how fast the tankless water heater will provide you with hot water.

When To Contact A Professional

Determining the size of a tankless water heater can be tricky for any homeowner. Most homes are fitted with a tank water heater. Tankless water heaters can be a rather new surprise for many homeowners. Calling on a professionally licensed master plumber is a great idea. They can calculate the size of a tankless water heater that you need based on your water output needs. Consequently, calling on your local home inspection team can help as well. They can inspect your entire plumbing system. Also, they can recommend a reputable master plumber to assist with the project.


When dealing with a water heater it is essential to understand the needs of your home, based on the size of the home. The more faucets and running water needed in the home will determine the size of your tankless water heater. Calling on a master plumber to assist with this item is a great idea. Additionally, reach out to your local home inspection team They can inspect your home and assist in determining how big of a tankless water heater is needed for your home. Call on House Inspection Associates to conduct a full home inspection in the Virginia, D.C., and Maryland areas.

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