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How Do Tankless Water Heaters Work?


A popular alternative to traditional water heaters, the tankless water heater provides hot water as needed rather than storing it in a tank. Some hot water tanks are 50+ gallons. It takes a lot of energy to heat and maintain that supply. Tankless models are more compact and efficient, but not every homeowner is familiar with them. This overview is intended to help you better understand what a tankless water heat is, how it works, and the pros and cons are.

What Is a Tankless Water Heater?

A tankless, or on-demand water heater, does not store water. Using electric power or a gas burner, it heats water directly as a sensor detects when the hot water faucet is turned on. The flow rate of the water heater, which determines the unit’s output, can range from 2 to 5 gallons per minute. A tankless gas water heater can generate a higher flow rate (and is often used as a whole house system) than a tankless electric water heater, which is generally used as a point-of-use model.

What Are the Pros of a Tankless Water Heater?

  • A near constant supply of hot water: A storage tank heater must heat a large volume of water at once, which takes time. Within seconds, a tankless water heater can begin supplying hot water, with less concern about running out.
  • Space savings: It can be installed in tight spaces such as a utility room, closet, or laundry room. If space is really limited, you can even install one on an outside wall.
  • Longer lifespan: While a traditional water heater has an average operating life of 8 to 10 years, tankless units can last up to 20 years, although hard water can reduce its useful life.
  • Energy efficiency: According to the U.S. Department of Energy, if you use 41 gallons of hot water or less per day, the water heater can be 24% to 34% more efficient, providing savings on your energy bill. Installing a demand water heater at each hot water outlet can yield up to 50% energy savings.
  • Natural gas conservation: The absence of a tank means there’s virtually no risk of a gas leak. For the same reason, tankless water heaters are much less prone to water leakage.

What Are the Cons of a Tankless Water Heater?

  • Higher cost to purchase/install: The upfront cost depends on the size and type of unit. Gas-fired models are generally more expensive. Generally, how cost-effective a unit is to use depends on efficiency and hot water demand.
  • Ability to supply multiple areas: Too much demand can stretch a tankless water heater to its limit. If you are taking a shower while someone else is doing the laundry, the water heater can fail; installing more than one tankless heater can resolve this.
  • Lag time: The unit remains off until you turn on the hot water tap. From startup to when hot water flows, you might wait a few seconds to nearly half a minute. Also, the heat exchanger will activate only when the flow rate is at least .5 gallons per minute.

Tankless Water Heaters: Making the Right Choice for Your Home

Whether a tankless water heater is right for your household depends on you needs and overall water usage. Cost and efficiency are the primary considerations. But if installation makes sense for you, an on-demand water heater can be a worthwhile investment.

Contact Cardinal Plumbing

Tankless water heaters offer comfort, efficiency, and convenience. At Cardinal Plumbing, we provide every homeowner in Northern Virginia with advice and service that suits their individual needs. We can install a tankless model for your bathroom or entire home. Open during the coronavirus pandemic, we’ve taken steps to keep every employee, technician, and customer safe by using hand sanitizer, disinfecting equipment and surfaces, and maintaining social distancing. To learn more and receive help from an experienced HVAC contractor, call 703-721-8888 or book your appointment online.

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