2 Terms You Should Know When Sizing Tankless Water Heaters

Unlike conventional water heaters that typically store 20-40 gallons of hot water in a tank for later use, tankless water heaters produce hot water on an as-needed basis. You get the amount you need when you need it — without the wasted energy of standby heat loss that occurs as water in a conventional storage tank cools. Turning on a hot water faucet induces the flow of cold water into the tankless heater’s heat exchanger where it’s quickly heated by a high-temperature electrical coil or a gas-fired burner.

When sizing a residential tankless water heater for your home, two main factors need to be considered: flow rate and temperature rise. Flow rate refers to the amount of hot water that you’ll need to provide for your home’s needs. Temperature rise is the difference between the unheated tap water coming into your home and your desired hot-water temperature.

When sizing tankless water heaters for your home, add the flow requirements (in gallons) of all hot water fixtures that are likely to be in use at any given time. Manufacturers rate tankless water heaters for consumers by providing a specification that expresses its temperature rise at a specific gallons per minute flow.  A tankless water heater might be rated with a 33 degree temperature rise at a flow of 2 gallons per minute. If your total flow requirements exceed 2 gallons per minute, you’ll get a temperature rise of less than 33 degrees and water that may not meet your temperature needs. On the other hand, the same unit might produce a higher temperature rise, such as 65 degrees, if the flow rate was cut to 1 gallon per minute. One way to address a shortfall in tankless water heater sizing is to reduce the total flow requirement by installing low-flow faucets and shower heads. Another way is to choose a tankless water heater with higher temperature rise and flow rate specifications. Finally, many homeowners decide to install more than one tankless water heater, in order to meet the demands of their home.

If this seems complicated, don’t hesitate to contact the experts at Geisel Heating, Air Conditioning & Plumbing for help. We’ve been serving homeowners in the greater Cleveland area for over 75 years.

Our goal is to help educate our customers 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.

Geisel Heating, Air Conditioning and Plumbing services Western Cleveland. Visit our website to see our special offers and get started today! For those Do it Yourselfers who would rather take control of your own indoor comfort, you can shop our online store for replacement parts, products and accessories!