How to Determine Tankless Water Heater Size for Optimal Efficiency

If you’re thinking of installing a tankless water heater, you have to keep in mind that available units come in different sizes and features. Tankless heaters from noted plumbing companies like Capital Plumbing & Heating Ltd., which serves Edmonton and nearby areas, come in two major types: gas-fired and electric heaters, and each one has its pros and cons.

Aside from the two major heater types, though, homeowners also need to take note of proper sizing. Electrical units come in smaller sizes and with less heating capacity. A general rule of thumb is that for one or two persons, an electric unit makes much more sense.

If more than two persons would require hot water regularly, gas-powered tankless heaters are the better choice. Getting the most optimal returns rests heavily on proper sizing, which is further explained as follows.

One of the most important things to remember is that, unlike older systems that make use of standard hot water tanks, tankless heaters are rated by the maximum possible temperature rise at a specified flow rate. In order to size a heater accordingly, you need to determine the flow rate and temperature rise required for its application. Determining the temperature rise is done by simply subtracting the incoming water temperature from the desired output temperature.

Determining the flow rate (the maximum amount of hot water a heater can provide at a given time, measured in gallons per minute, or gpm) is simple as well. To find the flow rate, one needs to calculate how much hot water is typically required at one time. This can be done by adding the flow rates of fixtures being used around the home.

For your reference, the following are the average flow rates for various applications: bathroom faucet-0.5-1.5 gpm; kitchen faucet-3-7 gpm; shower—1-2 GPM; dishwasher-1-2.5 gpm; and clothes washer-1.5-3 gpm. If determining the flow rate proves difficult, seek help from professional plumbers.

Once the overall flow rate and temperature rise are determined, you can go on to choose the heater size accordingly. Adding up the flow rates of fixtures and appliances requiring hot water holds the answer: the overall combined flow rate requires a water heater that exceeds the hot water demand.

For those looking to install a smaller (and cheaper) unit, lowering the overall flow rate is possible by installing low-flow water fixtures.

A properly sized water heater will adequately meet a household’s hot water needs, while also keeping utility bills down. This is why determining the right size is critical—the higher price tag of a tankless unit should be the only time you pay extra, not when the monthly bills come.

Capital Plumbing & Heating Ltd.

With over 20+ years of industry experience, Capital Plumbing offers the best in the business if you need expert plumbing, heating, cooling, or HVAC services in Edmonton that you can trust for the long term.