Skip to content
✓ Open Now
24/7 Service
Since 1989!

Schedule Now Call (253) 875-3350

Water Heater Guide Sizing A Tankless Water Heater

Tankless water heaters are gaining popularity among Sammamish homeowners because of their on demand hot water supply and space-saving design. Although they are more expensive than traditional tank water heaters, on demand water heaters are more efficient, reliable, and easier to install and maintain. Before choosing to install a tankless water heater, however, you will have to decide which size will meet your hot water needs.

Rather than storing hot water in a tank, the tankless models heat the water with individual units located near the application where hot water is needed, such as a shower or washing machine. For larger homes, some of these smaller units cannot heat enough water for several applications running at the same time. You can also install a single tankless water heater for the entire house, or separate ones for appliances that use more hot water.

Finding the proper size and type will depend on the flow rate—measured  by a GPM (gallons per minute) number—that each fixture needs. Every application has a standard flow rate that must be added up in order to calculate the hot water demands for your entire home. For instance, if someone is using a sink with a 1.5 GPM at the same time another person is running a shower with a 2.0 GPM, the flow rate for the tankless unit would need to be at least 3.5 gallons per minute. You will have to add up the flow rate for all the applications in the house to get the minimum GPM figure for your tankless water heater.

In addition to flow rates, tankless hot water heaters are also measured by how much the water temperature needs to rise as it moves through the heating unit. You can determine the temperature rise for each application by subtracting the temperature of water coming in from the desired temperature going out. Once you add those together with the overall flow rates, you will know which tankless water heater can handle your overall hot water needs.

Before you buy an on demand hot water heater, it is best to talk to a professional installer. While the flow rates and temperature rise for most household appliances are fairly standard, these numbers can vary because of several factors that professionals are trained to calculate. Size is not the only factor to consider when shopping for a tankless water heater. Fuel type and efficiency should also be factored in to your purchase, which is another reason to talk to a licensed Sammamish installer.