Water heaters are everywhere. Most of the time in a home you’ll see them in a closet in the garage, maybe a storage closet in a hallway or utility room, or sometimes even 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. There are also tankless water heaters that can be installed in many places, even outdoors on the side of a building.
The purpose of water heaters is to bring cold water in and push hot water out to use 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 light, however, it still needs electricity. An igniter is an electrical strike device akin to a lighter, which creates a spark. The spark is near a pilot light, which is essentially just a small flame that is constantly lit inside the unit. When the spark ignites the pilot light, a flame is produced that is large enough to heat the water at the bottom of the tank. That heated water then rises to the top where it is pulled out of the tank and pushed or drawn to water fixtures.
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 to be the disconnecting means. But the use of electricity is strictly for the ignitor, so it need not be more than a 15 amp, 125V receptacle in most cases.
Another reason it’s a good idea to install a receptacle near a water heater is that sometimes the water pressure is too low, and it needs to be boosted slightly to make sure it circulates as far as it can to get good pressure throughout the building. To achieve this, plumbers will often install a recirculating pump near a water heater, which needs to be plugged into a receptacle as well.
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. Cold water is run into the bottom of the tank, then is heated when the elements are energized. This warms the water at the top of the tank which is then pulled out when a faucet is turned on. 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 opened.
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 the various sinks in the house. These work in principally the same way, only 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 hot very quickly at that sink.
Tank electric water heaters are usually single or dual element units. Most 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.
Similarly, insta-hots need a source of power and a means to disconnect that power. Many people will direct wire insta-hots and disconnect them with a switch, or put in either a 120V or 240V receptacle so they can simply be unplugged.
How do we identify if a water heater is gas or electric?
When you look at a tank for a water heater, there are a couple of tells that identify it as gas or electric. First, an electric unit has access panels that can be removed where the elements are located. These often look like pill-shaped plastic covers usually found on the side of the tank near the top, or 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, so they won’t have either of these things on it. 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 a flexible gas line entering the bottom of the tank with a shutoff valve nearby is usually a dead giveaway that you’re dealing with a gas unit.