Tank vs. Tankless Water Heater: Which is Right for You?

What is the difference between tank and tankless water heaters?

The primary difference between tank and tankless water heaters lies in their approach to heating and storing water. Traditional tank water heaters store and pre-heat a set volume of water, maintaining it at a ready temperature S2. In contrast, tankless water heaters, also known as demand or instantaneous water heaters, heat water only when it's needed S2.

When a hot water faucet or appliance is used, cool water enters the tankless device S2. A heating element or igniter activates, warming the water as it travels through a heat exchanger before it leaves for the fixture S2. This on-demand heating process makes a hot water storage tank unnecessary, a major difference from traditional systems S2.

Tankless water heaters can run on electricity, natural gas, or propane S2. They typically outperform storage tank water heaters in efficiency because they do not waste energy by constantly heating and keeping large volumes of water ready for use S2. This constant readiness can consume a substantial amount of a storage water heater's daily operational energy S2.

Tankless units are measured by their hot water output in gallons per minute (GPM), whereas storage tank water heaters are defined by their tank capacity, such as 40, 50, or 75 gallons S2. These differing capacity metrics highlight their unique operating principles S2.

How do tankless water heaters save energy?

Tankless water heaters save energy primarily by avoiding standby heat loss, a common inefficiency in traditional storage tank models S2S3. Unlike storage water heaters that continuously heat and store water in a tank, tankless units only activate their heating element or igniter when a hot water faucet or appliance is turned on S2S3. This "on-demand" heating process means no energy is wasted keeping a large volume of water hot when it's not being used, which can account for a significant portion of a storage water heater's operating time S2.

To measure and compare the energy efficiency of water heaters, the industry uses the Uniform Energy Factor (UEF) S3. A higher UEF indicates greater efficiency, meaning the unit converts more of its consumed energy into usable hot water S3. This metric allows consumers to make informed decisions when choosing between different water heater types and models S3.

Gas-fueled tankless water heaters generally exhibit higher UEF ratings compared to their storage tank counterparts S3. Gas-fueled tankless models typically have UEFs ranging from 0.82 to 0.97 S3. In contrast, traditional gas-fueled storage tank heaters have UEFs from 0.63 to 0.95 S3. This difference highlights that the least efficient storage tank models can waste nearly 40% of the energy they consume to provide hot water, making tankless options a more energy-conscious choice S3.

While tankless water heaters offer significant energy savings, it's important to consider the overall costs, as initial installation can be higher, especially when switching from a traditional tank heater S1S3. However, their ability to eliminate standby energy losses makes them a more efficient option for many households S2S3.

What are the upfront costs and installation considerations?

The initial price and setup requirements for water heaters differ. High-efficiency models, such as tankless units, generally have a greater upfront expense compared to conventional tank heaters S3. Tankless water heaters, which are also referred to as demand, instantaneous continuous flow inline flash or instant on water heaters, can be purchased for electric, natural gas, and propane power sources S2.

The expense of installation can be considerable, especially when changing to a different kind of water heater S3. For instance, swapping out a tank water heater for a tankless model can be costly S1. Home Depot suggests that the average total installed cost of a tankless heater at $4,300, but this figure could increase if switching from a traditional tank heater S3. The price range for the units themselves is between about $800 and $2,600 S3.

Although tankless water heaters offer greater efficiency by avoiding the standby energy losses from keeping hot water stored, it may not always be economically wise to replace an existing tank unit with a tankless one S2S1. This is particularly the case for existing systems where the financial advantages may not justify the significant installation costs S1. Tankless heaters that run on gas are more efficient than gas storage water heaters and are small, fitting well in limited areas S3.

How much hot water can each type provide?

Tankless water heaters provide a continuous supply of hot water, whereas traditional tank water heaters have a limited capacity S2S4. Tankless units, also known as demand-type or instantaneous water heaters, heat water only when a faucet or appliance is activated S2. This on-demand heating ensures a consistent hot water supply temperature, as there is no storage tank to deplete S4.

Unlike tankless models, traditional tank water heaters store a predetermined amount of hot water S2. Their capacity is measured by the First Hour Rating (FHR), which indicates the total amount of hot water they can deliver in the first hour of use S3. The FHR can be found on the yellow Energy Guide label or in the manufacturer's specifications S3.

Tankless water heaters are not rated by FHR because they do not store water S3. Instead, their capacity is measured by the number of gallons of hot water they can produce per minute (GPM) S2S3. The output capacity of a tankless unit can be affected by the temperature of the incoming groundwater, meaning colder climates may require a higher GPM unit to meet household demands S2. When considering a tankless water heater, it's important to calculate your household's peak hot water demand to ensure the unit can adequately supply all fixtures and appliances simultaneously S2.

What are the advantages of tankless water heaters?

Tankless water heaters offer several benefits, including enhanced convenience and comfort due to their ability to provide a continuous supply of hot water S2. Unlike traditional storage water heaters, tankless units heat water on demand, eliminating the need to store large quantities of hot water and preventing energy waste from standby time S2. This period of inactivity can represent up to 96% of a storage water heater’s daily operational hours, consuming a significant amount of energy S2.

These systems can also help homeowners achieve the HERS Index Target for ENERGY STAR certification, contributing to a lower HERS Index for high-performance homes S2. The Uniform Energy Factor (UEF) measures efficiency, with higher percentages indicating greater efficiency S3. Gas-fueled tankless models typically have UEFs in the range of 0.82 to 0.97, outperforming gas storage tank heaters, which range from 0.63 to 0.95 S3. The least efficient gas-fueled storage models can squander almost 40 percent of the energy they use S3. Newer tankless models can even reach a UEF of up to 0.98 by utilizing condensing technology S3.

Tankless water heaters are available for all major energy sources, including electric, natural gas, and propane S2. While the core technology remains consistent across different models, their characteristics can differ based on the fuel used, physical dimensions, peak flow rate, and capacity S2. They feature precise temperature control and offer consistent hot water supply temperatures, ensuring a comfortable experience for the user S4. Additionally, these units are known for their low operating costs S4. Their compact size allows them to be typically mounted on a wall, saving space S3.

Which water heater is right for my home?

Choosing the right water heater for your home involves considering several factors, including your household's hot water needs, available space, and budget S3.

First, assess your hot water demands. While tankless heaters are efficient, some types may not deliver the required quantity of hot water for larger households S3. Tankless models are rated by gallons per minute (GPM), whereas tank heaters are rated by the number of gallons they hold S2S3.

Next, evaluate the available space in your basement or mechanical room, as your choices may be limited by the physical footprint of the unit S3. Tankless units are compact and typically wall-mounted S3.

Finally, consider the financial implications. While tankless heaters are more efficient, replacing an existing tank heater with a tankless one can be expensive, and it may not always make financial sense S1S3. The average installed cost for a tankless heater is estimated at $4,300, which can be higher if you are switching from a traditional tank heater S3.

Water Heater Comparison S3

Feature	Tank Water Heater	Tankless Water Heater
UEF	0.63 to 0.95	0.82 to 0.97 (up to 0.98 with condensing tech)
Upfront Cost	Varies	$800 to $2,600
Installation Cost	Varies	~$4,300 (average installed)
Hot Water Delivery	Limited by tank capacity, standby energy losses	On-demand, consistent supply, no standby losses

Tankless water heaters eliminate standby energy losses because they only heat water when it is needed S2S3. This on-demand heating can account for significant energy savings compared to tank heaters, which can spend up to 96% of their operating time storing hot water between uses S2.