Water Heaters 101

Water Heater Overview

Many factors determine which water heater is best for your home or business. The pre-screened plumbing professionals that we recommend at Best Plumbers®, service and install a full line of water heaters with the latest technologies, from high-capacity traditional tank units to tankless models that deliver a near endless supply of hot water and save energy. This guide will help you understand the different types of water heaters and the features you should look for. Its easy to feel confident about choosing the perfect hot water heater for your home when you hire one of our local experts.

Factors to consider in choosing a water heater

  • Fuel – Gas or electric
  • Water Storage – Tank or tankless
  • Function – Whole house or Point of Use

Water Heater Fuel Types
Most water heaters are fueled by gas or electricity. Refer to the table below to compare the differences between the two.


  • Requires a slightly larger up-front investment
  • Must be vented outdoors for safety
  • Units with sealed combustion or power venting increase safety
  • Usually cost less to operate
  • Not affected by power outages (tank-style only)


  • Generally cost less than gas models
  • Easy to maintain
  • Requires no combustibles or venting
  • Heats water quickly
  • Offer high energy factor ratings

Water Storage
Conventional tank water heaters store water in an insulated tank until it is needed. Tankless units do not store water but heat it by running it through coils. Each offer their own unique advantages, and you can compare features and benefits in the table below.

How a Water Heater Functions

Conventional Tank Water Heater
Stores constantly heated water inside the water heater tank of the unit.


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

Tankless Water Heaters

  • 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
  • Requires ventilation

Whole House and Point of Use Water Heater Systems
Conventional tank water heaters are whole house systems that send hot water from the tank through the house to the point where you want hot water. Tankless water heaters are typically whole house systems as well, heating water as needed. Whole house systems can provide hot water to more than one fixture at a time. Depending on the size of your home and the number of fixtures, you may need to consider adding additional hot water heating capacity. 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. Point of use systems typically augment a whole house system when instant or additional hot water is needed.

Other Criteria

Once you’ve determined the fuel, tank type and whether you want a whole house or point of use system, you’ll want to consider capacity, fuel efficiency, and size options.


It’s important to select a hot water heater that provides enough hot water for your home. An undersized water heater will work harder and have a shorter lifespan.

Conventional Tank Water Heaters

Determining the proper capacity for your household based on the number of bathrooms and bedrooms in your home. If you choose to purchase a unit with a tank, consult the table below for help in determining storage capacity.
Determine Water Heater Capacity

  • Number of Bathrooms

1 − 1.5
2 − 2.5
3 − 3.5

  • Number of Bedrooms

1 2 3
2 3 4 5
3 4 5 6

  • Minimum Tank Size

20 30 40
50 50 50 60
50 60 60 80


To determine the size of the tankless hot water heater you need, you’ll need to calculate how much hot water you’ll need at one time, which is called the flow rate. Flow rate is measured in gallons per minute (gpm). The table below provides typical flow rates for typical household hot water applications.
Typical Flow Rates

  • Bathroom Faucet

0.5 – 1.5 gpm

  • Low Flow Kitchen Faucet

3.0 – 7.0 gpm

  • Shower

1.0 – 2.0 gpm

  • Dishwasher

1.0 – 2.5 gpm

  • Clothes Washer

1.5 – 3.0 gpm

To determine the gpm you need, add the gpms of the major fixtures or appliances you expect to be using simultaneously. As an example, if you typically run the kitchen faucet (1.5 gpm) and the dishwasher (2.5 gpm) at the same time, you’ll need to heat 4.0 gpm of water. Once you have identified the maximum gpm required for your tankless unit, the next factor to consider is the temperature rise it needs to provide.


Once you know the capacity for your water heater, remember to take the unit’s dimensions into consideration. A new conventional storage replacement unit may be larger than the old one because more insulation is required to meet the latest strict federal energy standards. Keep this in mind where units are installed in closets or other close quarters.
If you are upgrading to a larger unit, you may need to have plumbing run to it if it has to be relocated. One way to avoid relocating the unit is to select a model in a non-standard size, such as a unit that is shorter but larger around, known as a “low boy” hot water heater.

If you are purchasing a tankless water heater, be sure the location you choose for installation meets ventilation requirements. The ideal location for a tankless unit 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.
The unit should have ½” clearance on the sides, 12” on the front and 18” off the floor.

Energy Efficiency

Whichever fuel source you use, a water heater can be the third largest energy user in your home! You’ll want a unit that offers energy and cost savings. Fortunately, however, almost all water heaters offer increased efficiencies to meet the increasingly strict federal energy standards. Always look for the Energy Factor (EF) rating on the unit. This rating measures how efficiently a unit converts energy into heat as well as how much heat is lost during storage. The higher the energy factor is, the more energy efficient the water heater will be. You should look for EF ratings as close to 1 as possible. Electric heaters tend to have the highest EF ratings.

Self Cleaning Water Heaters
Water heaters with a self-cleaning feature automatically fight lime and sediment buildup to lengthen tank life and maintain peak efficiency of the water heater for a longer period of time

Recovery Speed
This refers to the amount of time it takes to heat a full tank of water. You should look for a model with a fast recovery speed if you have a tendency to use a lot of hot water.

Automatic Shutoff Valve
This is a valve that helps prevent fires by shutting off the flow of gas if there’s movement in the ground or the gas flow experiences a sudden, sizeable increase.

If you have any questions on what type of water heater is best for you and your family, call on the highly trained professionals at Best Plumbers®

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