tankless water heater

What Size Tankless Water Heater Do I Need?

You can enjoy endless hot showers with the right size tankless water heater, even when the dishwasher is running. No more cold surprises, just comfort, and convenience for your entire family.

But what size do you need to enjoy the convenience?

To know the size of a tankless water heater you need, consider how many hot water fixtures (like showers and faucets) your family uses simultaneously. Then, pick a size that can heat enough water for all of them together.

If you need help determining the size of your tankless water heater or have questions regarding your water heater, call 623 777 4779. Our technician will answer your question and offer expert assistance.

Keep reading to discover how to pick the perfect tankless water heater for your home. 

What Size Tankless Water Heater Do I Need?

When choosing a tankless water heater for your home, consider the flow rate and rise in temperature needed for your household’s hot water demand. 

Start by listing all hot water devices you’ll use simultaneously, like showers and faucets, and add up their flow rates, measured in gallons per minute (GPM). This total is the flow rate your heater needs to support. 

For temperature rise, calculate the difference between your incoming water temperature (often around 50ºF if unknown) and your desired output temperature (typically 120ºF for general use, but possibly higher for specific applications like dishwashers). A common requirement is a 70ºF rise. 

Remember, tankless water heaters provide hot water on demand but have limits on flow rate and temperature rise simultaneously. For a family home, you might consider a gas-fired heater for higher flow rates or multiple units for extensive demands. This approach ensures a constant, efficient hot water supply catering to your family’s needs without compromising energy efficiency or space.

Factors to Consider When Choosing the Size of Your Tankless Water Heater

Consider flow rate, temperature rise, specific applications, fixture types, water quality, maintenance needs, energy source (gas or electric), and local regulations when selecting a tankless water heater.

  • Flow Rate and Simultaneous Usage: Determine the combined flow rate of all hot water devices you plan to use simultaneously. For instance, if you’re using a shower (2.5 GPM) and a kitchen faucet (0.75 GPM) simultaneously, you’ll need a heater that can handle at least 3.25 GPM.
  • Temperature Rise Requirement: Calculate the temperature rise by subtracting the incoming water temperature (assume 50ºF if unknown) from your desired output temperature (commonly 120ºF for household use). A higher temperature rise means a more powerful heater is required.
  • Specific Applications: Consider any special requirements, such as a dishwasher without an internal heater needing water at 140ºF, which requires a higher temperature rise.
  • Flow Rate Adjustments: Install low-flow water fixtures to reduce flow rates, making it easier for your tankless heater to provide consistent hot water.
  • Cold Water Sandwich Effect: Be aware of this effect, where cold water briefly flows before the hot water, which is common in tankless systems. It’s more noticeable in installations with lower usage frequency.
  • Water Quality and Maintenance: Hard water areas may require pre-treatment to prevent scale buildup in the heater. Regular maintenance is also crucial for optimal performance.
  • Electric vs. Gas Models: Gas-fired heaters typically offer higher flow rates than electric ones. Choose based on your home’s infrastructure and hot water demands.
  • Local Regulations and Health Standards: Check local codes, especially if the heater is for a food facility, as they may dictate specific temperature and flow rate requirements.

By considering these factors, homeowners can select a tankless water heater that efficiently meets their hot water needs while aligning with their home improvement goals.

Call 623 777 4779 For Tankless Water Heater Installation 

Selecting the ideal tankless water heater ensures convenience for your household. You also need professional installation to enjoy an instant hot water supply. That’s where Grand Canyon Home Services comes in. Since 1998, we’ve been the trusted name in the West Valley area for emergency plumbing, electrical, and HVAC services. 

Our team offers flexible scheduling, 24-hour live answer lines, and a commitment to providing service at competitive, upfront prices.

Don’t compromise on your family’s comfort and well-being. For swift, reliable tankless water heater installation, indoor maintenance, and repair solutions, call us at 623 777 4779. Let Grand Canyon Home Services care for your water heater needs with the expertise and dedication you deserve.


How do I determine what size tankless water heater I need?

To determine the size, calculate the total flow rate of all fixtures used simultaneously and the required temperature rise from incoming to desired water temperature. Consider household size, usage patterns, and energy source (electric or gas).

How big of a tankless hot water heater do I need for a family of 4?

For a family of 4, a heater with a flow rate of about 5-8 GPM is ideal, considering multiple showers and appliances might be used concurrently. Ensure it can provide a temperature rise suitable for your region’s incoming water temperature.

How big of a tankless water heater do I need to replace a 40-gallon water heater?

Replacing a 40-gallon water heater usually requires a tankless unit with a flow rate of 5-7 GPM, accommodating typical household hot water usage. Assess your peak hot water demand to choose the right size accurately.

Can a tankless water heater be too big?

A tankless water heater can be too big if its capacity significantly exceeds household demand, leading to unnecessary energy consumption and higher costs. It’s important to size it correctly based on actual usage needs.

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