How Does a Water Heater Work?

Water heaters are everywhere. Most of the time, in a home, you’ll see them in a closet in the garage, or maybe in a storage closet in a hallway or utility room. You can even sometimes find them in attics or basements. In commercial buildings, you might find them above a grid ceiling or in a storage room or water closet. They look like a large cylinder or tube with piping at the top for water to flow in and out. Tankless water heaters offer the flexibility of installation in various locations, including outdoor placement on the side of a building.

The purpose of water heaters is to bring cold water in and push hot water out. Enabling you to use hot water at all of the various sinks, tubs, and showers throughout the building. They typically heat the water using electric heating elements inside, in the case of electric water heaters. Or by igniting a gas like propane or natural gas to provide a physical flame. Both are common in dwellings, but the means of heating will change how electricians wire for them.

Gas Water Heaters

Gas water heaters heat the water inside the tank using fire, similar to how a stove heats a pot. For that fire to be lit, it still needs electricity. An igniter is an electrical strike device akin to a lighter that creates a spark. The spark is near a pilot light. This is essentially just a small flame that is constantly lit inside the unit. When the spark ignites the pilot light, it produces a flame large enough to heat the water at the bottom of the tank similar to how a gas stove works. That heated water then rises to the top, where it is pulled out of the tank and pushed or drawn to water fixtures.

For older models of gas water heaters, the burner is ignited by a pilot light. This is a small flame that is constantly burning. Waiting to ignite the main burner when the water needs to be heated. When the thermostat signals that the water temperature has dropped below the set level, it opens the gas valve. Then the gas flowing to the main burner is ignited by the pilot light.

In newer models, the pilot light has been replaced by electronic ignition systems. Which only ignite the burner when heat is needed, improving energy efficiency. Some types use an intermittent pilot (IP) ignition. Which uses an electric spark to ignite the gas when the thermostat calls for heat. Other types use a hot surface ignition (HSI). This is where an electronically controlled resistance heating element warms up to a temperature high enough to ignite the gas.

Gas Water Heaters Still Need Power

Once the burner ignites, it heats the water at the bottom of the tank. The heated water then rises to the top due to natural convection, where it is drawn off by the domestic hot water piping whenever a hot water tap is opened in the home.

Gas water heaters, therefore, still require a receptacle nearby to be provided for the ignitor. Some models of water heaters are direct-wired and require a switch to be used as a disconnecting means. Others use a receptacle and a plug-in cord as the disconnecting means. But the use of electricity is strictly for the ignitor. So it need not be more than a 15-amp, 125-V receptacle in most cases. Rather than using this electricity to be the driving force for heat, it just provides a momentary ignition source for the fuel.

Another reason to install a receptacle near a water heater is that water pressure in the system can sometimes be too low, necessitating the use of a recirculating pump to enhance pressure. A recirculating pump helps ensure that water is efficiently circulated throughout the building, providing consistent and adequate water pressure. Plumbers often install these pumps near water heaters, and they need to be plugged into a receptacle to function properly. This installation helps maintain optimal water flow and pressure, improving the overall performance of the water heating system.

Electric Water Heaters

Electric water heaters differ slightly in how they heat the water. Rather than running natural gas or propane to the heater and lighting a flame, electric water heaters utilize heating elements similar to those you would find in a toaster. Instead of heating bread, they heat water. We introduce cold water into the bottom of the tank, and then the elements heat it up when energized. When a faucet is on, it draws out the warm water from the top of the tank. The reason it takes a few seconds (or minutes, in some cases) to get the hot water to a faucet is that the warm water in the tank has to make its way to the faucet once it’s open.

Electric water heaters come in various configurations, each designed to meet different household needs. Among the most common configurations are single element and dual element water heaters, each with its unique advantages and applications.

Single Element Heaters

Contain one heating element located near the bottom of the tank. This single element is responsible for heating the entire volume of water within the tank. Because only one element is working to heat all the water, single element heaters often experience slower recovery times. This means it takes longer to heat the water after the initial supply has been used. These types of heaters are typically found in smaller tanks or in applications where the demand for hot water is lower. Making them suitable for small households or secondary water heating needs.

Dual Element Heaters

On the other hand, feature two heating elements: one positioned at the top and the other at the bottom of the tank. The lower element heats the water at the bottom of the tank, while the upper element heats the water at the top. The presence of two heating elements allows for faster recovery times. This is because they can work simultaneously to heat the water more quickly. During periods of high demand, the upper element can quickly heat the water at the top of the tank, ensuring a rapid supply of hot water to the outlets. This configuration is ideal for larger households or situations where there is a high demand for hot water throughout the day.

Most electric water heaters require a 240-volt power supply. This higher voltage is necessary because it provides the energy needed to heat the elements efficiently, and in this case electricity is doing all of the work rather than gas. The use of a 240V power supply allows for more power to be delivered to the heating elements, resulting in quicker heating times and more efficient operation.

Insta-Hot Water Heaters

Some people don’t like waiting for the water to arrive at the faucet, so they will have an electrician install an “instant-hot” (usually called an Insta-Hot) water heater under various sinks in the house. These work principally in the same way, except there is no tank. The Insta-Hot is just another heating element connected to the hot water side of the sink. When the water begins to flow, the heating element energizes; since it just has to heat the water flowing past the element, the water can get very hot quickly at that sink.

Tank electric water heaters are usually single or dual-element units. Most, but not all, require 240V power to heat the water, in which case it’s common to install a disconnect near the water heater. Feeders are normally run from an electrical panel to the disconnect. Then, from the disconnect, the same wires run to wire leads located on the top of the tank. This way, maintenance personnel can easily disconnect the unit from electricity and work on it. Insta-Hots need a source of power and a means to disconnect that power. Many people choose to either directly wire Insta-Hots and disconnect them using a switch, or install a 120V or 240V receptacle for easy unplugging.

How to identify if a water heater is gas or electric

When you look at a tank for a water heater, there are a couple of things that identify it as gas or electric. To begin with, an electric unit features removable access panels that provide access to the location of the elements. These often look like pill-shaped plastic covers, usually found on the side of the tank near the top, bottom, or both. Another sign that a tanked water heater is electric is that there is a place for incoming wiring to hook up on the top of the tank. There will normally be a metal cover with a couple of screws holding it in place. When you remove the screws, you’ll find a black and a red wire inside, along with a green screw for terminating the equipment grounding conductor (ground).

Gas water heaters don’t have electric heating elements or an electrical junction box on the top. What you will notice are gas lines and copper piping around a gas water heater. Electric water heaters may have copper tubing as well, but typically they’ll have a flexible gas line entering the bottom of the tank with a shutoff valve nearby; which is usually a dead giveaway that you’re dealing with a gas unit.

Conclusion

Water heaters, essential for providing hot water in homes and commercial buildings, come in various forms and installations. Electric water heaters use heating elements, similar to a toaster, to warm water, while gas water heaters utilize a burner ignited by a pilot light or electronic ignition. These heaters can be found in closets, garages, attics, and basements, and their placement affects accessibility and efficiency. Recirculating pumps, often installed near water heaters, help maintain consistent water pressure throughout the building. Choosing between single element and dual element electric heaters depends on the hot water demand, with single element heaters being suitable for smaller needs and dual element heaters offering faster recovery times for larger households. Understanding these differences ensures optimal performance and safety, tailored to specific household or commercial requirements. Check out the “Heat Pump vs Air Conditioner and Furnace” next!