Tank Water Heater

Tank water heaters are traditional water heaters that work with gas and electric fuel sources. They offer a large volume of hot water that can be dispersed to your entire home. Tank water heaters typically keep the stored water at a temperature near 120 degrees Fahrenheit at all times.

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Tankless water heaters do not store heated water, but rather heat water only as it is needed. They also work with gas and electric fuel sources.

While they should be installed close to their most common point of use, they can service the whole house. Their temperature can be adjusted as often as desired, and they are popular for being eco-friendly alternatives to traditional tank water heaters.

Depending upon your family’s water usage, you may need more than one tankless water heater.

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Hybrid water heaters use advanced heat pump technology to pull in the ambient air and extract the heat to warm the water. They also service the whole house.

Point of use systems are individual units that install directly under the sink or in a closet. These systems deliver instant hot water to a specific location without wait time. Point of use systems typically augment a whole house system when instant or additional hot water is needed.

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Water heaters are responsible for heating your home or office's supply of water and immediately supplying that hot water to fixtures and appliances.

This guide will help you learn which size and type of water heater is best for your needs. It will also show you how to calculate the amount of water your family uses and how much space you need to allot for your water heater.

We highly recommend having your water heater installed by a professional as it is a difficult and sometimes dangerous process.

Note: Nationwide energy-efficiency regulations set in 2015 impact people buying new or replacing old hot water heaters. Your old water heater model number may not be the same as your new model number, so make sure to purchase based on capacity size instead of model number. Additionally, the size of all water heater tanks have increased, while the amount of water that they hold has decreased. Measure the space you have available for your water heater carefully so you can accurately judge what size water heater will fit. Learn more through Rheem’s National Appliance Energy Conservation Act guide.

Tank vs. Tankless
Choose between a traditional tank water heater or a smaller, eco-friendly tankless water heater.

Type How it Functions Factors to Consider

Conventional Tank

Stores constantly heated water

  • Economical
  • Can be positioned in closet, basement, or garage
  • Capacity ranges from 20 to 80 gallons
  • Efficiency varies between models, brands, and fuel sources


Heats cold water with a gas burner or electric element as it passes through the water heater

  • Require a larger up-front investment
  • Hang on wall and frees up floor space
  • Excellent option for residences occupied part-time
  • Reduce energy consumption by as much as 30%
  • Can run out of hot water during heavy usage
  • Require ventilation


Heats cold water via an electrical heating element and heat pump that pulls in ambient air and extracts the available heat

  • Require a larger up-front investment
  • Magnesium anode rod extends life of the tank
  • Heat pump delivers more hot water, up to 33 percent faster than standard electric water heater

How to Choose a Water Heater

First, identify your fuel type: natural gas, propane or electric. Then decide if you’d prefer tank or tankless. Next, use the calculations below to determine the size you need.

Tank Water Heaters

Determine your required gallon capacity based on the number of people who will regularly be using hot water in your home.

Household Size Gallon Capacity

1 – 2

23 – 36

2 – 4

36 – 46

3 – 5

46 – 56

5 or more

56 or higher

Note: Your new water heater will likely be larger than your old one due to 2015 regulations requiring more insulation around the water tank. If you find you’ve run out of space in your current water heater cabinet, instead of relocating your unit, ask a Dunright associate about non-standard sizes, such as a “low boy” model, which is shorter and wider.

Tankless Water Heaters

1. Calculate how much hot water you need at any time.

Use this chart to calculate the gallons per minute (GPM) of hot water each of your fixtures and appliances needs and add up these amounts to get a total GPM for your household.

For example, if you typically have one shower running, plus a dishwasher, and the clothes washer, you have a flow rate of 3.5-7.5 GPM.

Fixture/Appliance Typical Flow Rates

Bathroom Faucet

0.5 – 1.5 GPM

Kitchen Faucet

3.0 – 7.0 GPM


1.0 – 2.0 GPM


1.0 – 2.5 GPM

Clothes Washer

1.5 – 3.0 GPM

Calculate Temperature - Water Heater

2. Determine your home’s required temperature rise

Calculate the difference between your ground water temperature and your desired hot water temperature – typically around 120 degrees Fahrenheit. This is your required temperature rise.

For example, if you live in Atlanta, you have a ground water temperature of 62 degrees Fahrenheit. To reach an ideal hot water temperature of 120 degrees Fahrenheit, subtract 62 from 120. You have a required temperature rise of 58 degrees Fahrenheit.

Use the EPA’s map for average groundwater temperature for guidance.

3. Pick your water heater unit

Use your GPM and required temperature rise to determine which units will meet your needs. Each product information page on the water heater's manufacturer website includes this information, as do labels on the units.

Feel free to ask a Dunright associate questions about your purchase, or contact our Installation Services team for help and installation.

Energy Efficiency & Installation Tips

Look for the Energy Factor (EF) rating. The higher the EF, the more energy efficient the unit is.

Most water heaters offer increased efficiencies to meet federal standards. The EF rating measures how efficiently a unit converts energy into heat as well as how much heat is lost during storage.

Look for EF ratings as close to 1 as possible. Electric heaters tend to have the highest EF ratings.

Tankless water heater Installation Tips

  • Be sure the location you choose for installation meets ventilation requirements.
  • The ideal location is on an exterior wall near a gas supply line, water supply line and electrical power source. This is also the easiest and most cost-effective way to run the venting.

Tank water heater Installation Tips

  • We urge you to consider professional installation for tank water heaters for your safety.
  • The unit should have ½-inch clearance on the sides, 12 inches on the front and 18 inches off the floor.
  • Hybrids offer a narrow 21-inch diameter for access into smaller locations.

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We are happy to discuss any questions you have regarding water heaters.