Thumbnail: Adam’s 50 gallon water tank replacement
Whether you’re looking to cut down on your power bill or just want to replace an old, faulty tank heater, there’s a lot to love about going tankless. With its compact, energy-saving design and nearly endless supply of hot water, the higher price tag quickly feels worth it.
Assuming you’re looking to replace a 50-gallon tank water heater with a tankless version, it’s crucial to know the right size for your household needs. In this article, I’ll walk you through how to choose the perfect tankless water heater for your home by considering things like your home’s size, climate, and water usage.
The Short Answer (for replacing a 50-gallon heater)
Generally, if you’re up north, a 10 GPM tankless heater should work just fine. If you’re further south, you might only need a 7 GPM model.
Skip to the bottom of the article for 3 examples of 10gpm and 3 examples of 7gpm tankless water heaters.
The 2 factors to Consider (GPM and Temperature Rise)
Gallons Per Minute (GPM)
GPM tells you how much water the heater can supply at once, so it’s helpful to think about how much hot water your household uses at the same time—like running the shower, dishwasher, and laundry together. If you’ve got a big household, reaching peak usage is more likely, so going with a higher GPM will help keep your water flow and temperature steady. Larger households are more likely to reach peak water usage, making it crucial to choose a heater with an adequate GPM to maintain consistent water flow and temperature.
Calculating GPM
Flow Rate (GPM) measures how much water your household uses during peak usage.
A typical GPM looks something like this:
Shower: 1.5-3 GPM
Dishwasher: 2-4 GPM
Washing machine: 3-5 GPM
For instance, if your dishwasher (3 GPM), washing machine (4 GPM), and shower (2.5 GPM) are all running simultaneously, your flow rate would be 9.5 GPM.
Temperature Rise
Temperature rise is simply the difference between your incoming groundwater temperature and the hot water temperature you want (like 105°F minus 60°F, for a 45°F rise). Since groundwater temperatures vary by region, a tankless heater that works well in a warm climate might struggle to keep up in colder areas. In colder climates, you’ll need a more powerful heater to achieve the same water temperature.
Calculating Temperature Rise
Temperature Rise is the difference between the temperature of incoming water and your desired hot water temperature. Refer to the chart below for average groundwater temperatures across the U.S., which will help you gauge the heater size suitable for your area.
Regional variations in U.S. groundwater temperatures, with colder averages in the north and warmer conditions in the south.
Swapping out a bulky 50-gallon tank for a tankless water heater is a great way to save energy and space in one go. To choose the right size, consider your household’s peak water usage (GPM) and the necessary temperature rise for your area. Consulting a local expert can be invaluable—they can recommend the best model for your climate and plumbing, helping you avoid costly mistakes. With the right tankless heater and guidance, you’ll enjoy steady hot water and long-term energy savings.
Hey, I’m Adam Miller. After years of crawling through cramped basements fixing water heaters (and discovering some pretty questionable DIY attempts), I figured it was time to share what I’ve learned in a way that doesn’t involve me getting covered in dust. I started this site to help you make sense of the whole tankless water heater thing—whether you’re tired of cold showers or just want to save a few bucks on your energy bill. I like to keep things simple, practical, and if I can throw in a bad joke or two along the way, even better!
