Unlike storage water heaters that can heat 40 to 50 gallons of water at a time, a tankless water heater heats your water on demand. When you turn on the faucet or decide to do your laundry, that’s when the tankless water heater springs into action. This can save money on heating water without suffering hot water losses, if you size the tankless heater correctly. However, you are no longer going by stored gallons. The key is in learning how to calculate your flow rate.
Steps to Size Your Tankless Water Heater
Are you trying to decide between a tankless or a storage hot water heater? Try sizing both. To size the tankless water heater, so that you don't run out of hot water doing too many things at once, do the following:
Find typical flow rates – Flow rates are averaged out for different types of faucets, showerheads, dishes and clothes washers. If you’ve installed low-flow faucets and showerheads, they will tell you on the package the gallons per minute (gpm) rating. Otherwise, you can estimate the flow rate by getting an average rate for typical faucets for specific manufacturers.
Estimate Concurrent Use – Do you run your dishwasher while you’re running the laundry? Do you take a shower while cooking dinner? These behaviors will impact your total flow rate. To get the typical flow rate of hot water for your household add the gpms for each item run at the same time to arrive at a total on-demand gpm.
Avoid Wasting Hot Water – Check to make sure you have a tight system with no leaky faucets. Plan to use your hot water at different times, if you think you want a lower gpm tankless heater model or use point-of-use tankless water heaters in discrete areas like kitchens and baths.
Our goal is to help educate our customers in Calgary, Alberta about energy and home comfort issues (specific to HVAC systems). For more information about tankless water heaters and other HVAC topics, download our free Home Comfort Resource guide. Image courtesy of Shutterstock