Inefficiency doesn’t only mean being wasteful of energy, but also of time and resources. Having too little hot water can be just as bad as having too much at any given moment. To avoid this, make some speedy calculations on your overall hot water demand. The Department of Energy offers several effective tips on calculating demand for each type of water heater in Athens, GA and elsewhere.



Tankless water heaters don’t store hot water in reserve. Instead, they heat the water as it flows through the unit, providing as much hot water as needed without running out. So, instead of the capacity, compute for the flow rate and temperature rise.

While doing the math, it’s important to always take simultaneous use into account. There will always be one person who will brush his or her teeth while you’re taking a bath. If you have a 2.0 gpm showerhead and a 0.5 gpm faucet, the tankless unit must be capable of providing 2.5 gpm, whether or not both fixtures are open at the same time.

Meanwhile, the temperature rise is the difference between the thermostat temperature and the temperature of groundwater. Athens lies in the northern half of Georgia, so the temperature of groundwater there can play between 62 and 67 degrees. To achieve 120 degrees as suggested by the Department of Energy, the tankless unit must achieve a 53- to 58-degree rise.


For tank-type heaters, the Department of Energy recommends getting their first-hour rating (also called first-hour delivery), which refers to the amount of hot water they can deliver within the first hour of operation. You can see the rating in the ENERGYGUIDE stickers, which must fulfill your peak hour demand.

To calculate for the peak hour demand, draw up a table and list your frequent applications of hot water and their average use rate. Determine how many times you perform the application within one hour and multiply to get the result. Add the multiplied results to determine the overall peak hour demand. The correct first-hour rating must be within two gallons of the peak hour demand.

Such calculations won’t matter, though, if the heater of your choice isn’t in working condition. Remember to call Athens, GA plumbing firms like Athens Plumbing & Well Service for repairs, maintenance, and assistance.

(Source: Sizing a New Water Heater, Department of Energy)