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Sizing a Tankless Water Heater

what size tankless water heater do i need

Home water heater systems in Columbus, OH, are specific to each house — there isn't a one-size-fits-all solution, and a water heater is no exception. If you're interested in a tankless water heater for your home but don't know what size you need, you've come to the right place. Read on to learn why size is important to your unit's efficiency and service life and how to calculate what size tankless water heater you need. 

Why Tankless Water Heater Sizing Matters

Like your furnace, AC, and electrical panel, your tankless water heater should meet your home’s demands. Many people choose the same size they previously had, but if you’re moving from a tank to a tankless system, it’s not always a simple swap. Water heaters have improved in efficiency, and your needs may have changed since the last time you purchased a water heater system.

Buying a small unit to save money is tempting, but it may not be enough for your hot water needs. For example, if you try to run the dishwasher while taking a shower, you’ll likely get blasts of cold water as the cycles run. As the unit tries to keep up with demand, it’ll likely overwork and break down sooner than expected. Frequent repairs or early replacement can wind up costing you more in the long run.  

Purchasing an oversized unit also has drawbacks. They often consume more energy, which translates to higher operating costs. 

The right size tankless water heater for your home should consistently provide hot water when and where you need it.  

Key Factors Determining Your Needs

Before we discuss how the pros calculate the best water heater size for your household, let’s go over some other factors that can influence your needs.

Gas or electric 

First, decide if you want an electric or gas system. Natural gas is cheaper in Ohio than the cost of electricity, which translates to lower operating costs. However, electric systems can be efficient for households with lower hot water needs and rural locations with limited infrastructure. The choice between gas or electric influences the cost to install a tankless water heater in your home.

Space requirements

Tankless systems are notoriously more compact than traditional tanked heaters. You can install them in a crawlspace, garage, under stairs, or in a cupboard. Ensure you have ample space around the unit so you don’t accidentally bump it with your car or bury it behind stored items. Dents and structural damage can decrease the efficiency and functionality of any tank or tankless system.

One of the great things about a tankless system is you can have more than one. They can work in tandem, or you may choose to install smaller systems for specific appliances, like under the sink for your dishwasher. If you're installing into a small space or placing more than one unit throughout your home, the installation process with electric models is cheaper and less complicated. 

Evaluate your demand

Finally, you'll need to assess your hot water needs. Consider how many water-dependent appliances you have, the number of bathrooms in your home, and whether you run one or more showers at the same time.

How Professionals Calculate Size

Calculating what size tankless water heater you need to meet your household's demands can be complicated if you don't know where to begin. When you hire a professional for a tankless water heater replacement estimate, they’ll use a magic formula to assess your needs. 

The magic formula: GPM and temperature rise

The first step is calculating your flow rate in gallons per minute (GPM). Professionals do this by evaluating the peak hot water usage. They measure the flow rate of the fixtures you want to use simultaneously and/or the appliances used during peak times.

You may need to look up the GMP for your appliances on the manufacturer's website. Most professional plumbers can quickly estimate the flow rate based on their experience and knowledge of water-dependent appliances.

Next, calculate the temperature rise or the difference between the incoming cold water and the desired hot water temperature. Climate can impact the incoming water temperature. Check the EPA groundwater map to get a general idea of the groundwater in your area. The greater the difference, the fewer fixtures your system can supply on demand.

The results of these two assessments determine the size of the tankless water heater you'll need.

Getting a Personalized Assessment

Consult with a professional to take the headache and guesswork out of the equation. Our expert plumbers are standing by to help you with your water heater needs. We’ll listen to your concerns, provide a personalized assessment of your needs, and work with you to find the best system for you. We work with small and large gas and electric systems. 

Size Matters!

Whether replacing an existing tankless system or upgrading from a traditional water heater, size matters. A tankless system should meet your home's demands without overworking or draining your utilities.

Call Apex Today

Call the pros at Apex, Plumbing, Heating, and Air for a tankless water heater installer near you. We offer fast, reliable service and free, no-obligation estimates. Contact us today to schedule a consultation or to book a professional tankless water heater installation.