Water Heating Systems Explained and Compared

Water heating systems are a crucial part of any home, providing hot water for daily use.

There are three main types of water heating systems: tankless, tank, and heat pump systems.

Tankless systems heat water as needed, providing continuous hot water without the need for a storage tank.

Tank systems, on the other hand, store hot water in a tank, which can be a space-consuming option.

Heat pump systems use refrigeration to heat water, making them a more energy-efficient option.

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In the US, it's common for hot water to be heated by fossil fuels in a boiler, while potable water is heated in a separate appliance.

Conventional storage water heaters offer a ready reservoir of hot water, but may not be enough for everyday use, especially when multiple people are using hot water at the same time.

Tankless or demand-type water heaters heat water directly without a storage tank, providing a constant supply of hot water without running out.

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Here are the main types of water heaters:

These types of water heaters vary in terms of efficiency and cost to operate, with some, like heat pump water heaters, being extremely efficient and offering significant cost savings.

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There are several types of water heating appliances, each with its own set of characteristics and advantages.

Conventional storage water heaters are still the most common type, with a tank capacity of 30 to 80 gallons. They're fueled by natural gas, propane, electricity, or oil, and can heat water quickly, but are less efficient than other options.

Tankless or demand-type water heaters heat water directly without a storage tank, making them ideal for homes with multiple hot water users. They're designed to provide an adequate supply of hot water without running out.

Heat pump water heaters move heat from one place to another instead of generating heat directly, resulting in high efficiencies and significant cost savings. They require open room with 6' or higher ceiling and a condensate drain.

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Solar water heaters use the sun's heat to provide hot water, saving money on energy bills. They come in various types, including direct-gain and indirect or closed-loop systems.

Electric water heaters use electric resistance elements to heat water, offering low upfront costs and compact versions. However, they require an expensive upgrade of the home's electrical capacity.

Tankless (on-demand) water heaters use a heat exchanger to heat water as needed, delivering a constant supply of hot water. They're ideal for homes with low hot water usage, but may not support simultaneous hot water usage.

Here's a summary of the different types of water heaters:

Electric water heaters can be a cost-effective option, but they may not be the most efficient choice. In fact, electric tanked water heaters received midrange scores on energy efficiency and low-level scores for energy consumption costs.

Electric water heaters, especially those with the ENERGY STAR certification, can save a household of four around $600 per year on their electric bills. This translates to more than $4,500 in savings over their lifetime.

Heat pump water heaters, on the other hand, use a hybrid system that produces hot water efficiently in both warm and cold climates. This makes them a super-efficient option.

These water heaters can be a worthwhile investment, especially for larger families that use more hot water. In fact, a household of four can save even more with a heat pump water heater, with the savings paying back the difference in about three years.

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Heat pump water heaters are highly efficient, using two to four times less energy than traditional electric water heaters.

These units can be installed as a replacement for gas-fired water heaters without requiring extra electrical work or increased panel capacity.

Some heat pump water heaters have a "hybrid" mode, allowing them to operate like a conventional water heater if they're not keeping up with demand.

However, heat pump water heaters have a higher up-front cost, though current tax incentives can reduce pay-back time to a few years.

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Storage tank water heaters, on the other hand, are still the most common type, continuously storing heated water and fueled by natural gas, propane, electricity, or oil.

Gas water heaters generally cost less to run than electric water heaters, but cost more at the time of purchase.

Overall, storage tank water heaters have a lower up-front cost, but are much less efficient than heat pump water heaters.

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In the UK and Ireland, a traditional gravity-fed system uses a space-heating water boiler to heat potable water in a cylindrical vessel.

This vessel is usually made of copper and is supplied from a cold water storage vessel or container, often located in the roof space of the building.

The system produces a steady supply of domestic hot water at low static pressure head but usually with a good flow.

In most other parts of the world, water heating appliances heat water at pressures close to that of the incoming mains water supply, without the need for a separate cold water storage vessel.

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A heat exchanger is used to transfer heat from the space-heating boiler to the water heater vessel/container.

The boiler operates at a higher temperature than the potable hot water supply, which is a common arrangement in traditional plumbing in the UK.

Most potable water heaters in North America are completely separate from the space heating units, due to the popularity of HVAC/forced air systems in this region.

For larger buildings with intermittent or occasional hot water use, multiple point-of-use (POU) water heaters may be a better choice.

This is because POU water heaters can reduce long waits for hot water to arrive from a remote heater.

Centralized water heaters are more traditional, and are still a good choice for small buildings.

However, they may not be suitable for larger buildings with varying hot water demands.

The decision where to locate the water heater(s) is only partially independent of the choice of a tanked vs. tankless water heater.

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Storage Tank Water Heaters are still the most common type. They continuously store heated water and are fueled by natural gas, propane, electricity, or oil.

Typically, they have a tank capacity of 30 to 80 gallons. This range can vary depending on the household's needs.

Gas water heaters generally cost less to run, by about half, compared to electric water heaters. However, gas models cost more at the time of purchase.

Storage Tank Water Heaters have a few notable characteristics. They can heat water quickly, which is a significant advantage for households with high hot water demands.

However, they are much less efficient than heat pump water heaters, and slightly less efficient than gas tankless units. This means higher costs over time for households relying on Storage Tank Water Heaters.

Here are some key factors to consider when choosing a Storage Tank Water Heater:

The fuel type you choose for your water heater will significantly impact its size, energy efficiency, and annual operation costs.

Electricity is widely available in the United States and can be used with various water heater types, including conventional storage, tankless, and heat pump water heaters.

Natural gas is available in many areas and can fuel conventional storage and demand water heaters, as well as combination water and space heating systems.

Propane is also widely available and can be used with conventional storage and demand water heaters, as well as indirect combination water and space heating systems.

Geothermal energy is available throughout the United States for those with a geothermal heat pump system installed in their homes.

Solar energy is available throughout the United States, with the most abundant resources in the Southwest, for solar water heaters.

Consider the following fuel types and their availability in your area:

Condensing water heaters are a high-efficiency option that can deliver more hot water than standard gas water heaters while using less energy.

They work by capturing exhaust gases and transferring the heat to incoming cold water, making them a good choice for properties that heat with gas and need a unit with a capacity of more than 55 gallons.

These models have a tank like a conventional water heater, but with better insulation and more efficient burners, which can be a plus for Energy Star certified models.

Higher initial costs are a drawback, although Energy Star certified models may be eligible for a tax credit through 2025.

Proper venting and a condensate drain are also required for installation, which can add complexity to the process.

Overall, condensing water heaters are worth considering for those who want to save on energy costs and have a larger water heater capacity.

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Electricity is a widely available fuel type in the United States, suitable for conventional storage, tankless, or demand-type water heaters, as well as combination water and space heating systems.

Fuel oil is available in some areas, mainly for conventional storage water heaters and indirect combination water and space heating systems.

Geothermal energy is available throughout the United States for those with or planning to have a geothermal heat pump system.

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Natural gas is available in many areas to fuel conventional storage and demand water heaters, as well as combination water and space heating systems.

Propane is also available in many areas to fuel conventional storage and demand water heaters, as well as indirect combination water and space heating systems.

Solar energy is available throughout the United States, with the most abundant resources in the Southwest, for solar water heaters.

Comparing fuel costs is essential, especially if you have multiple options available in your area. Contact your utility for current fuel costs or rates to make an informed decision.

The type of water heater you choose affects your water heating costs, and one type may use a fuel type more efficiently than another. For example, an electric heat pump water heater is often more energy efficient than an electric conventional storage water heater.

The following table summarizes the fuel types and their availability in the United States:

If you're looking for a water heater that's backed by a reputable organization, consider one that's earned the ENERGY STAR certification. These models have been independently tested and meet certain energy efficiency standards.

The ENERGY STAR certification is a mark of excellence, and models that have earned it come with a minimum 6-year manufacturer warranty for added peace of mind.

You can find ENERGY STAR certified water heaters in various types, including electric heat pump, gas, and tankless models. These models are not only more efficient but also quieter than their predecessors.

Here's a quick rundown of the types of water heaters that have received high scores for energy efficiency, including:

Keep in mind that even within the same type, individual models can vary in performance, so it's essential to research and compare different options before making a decision.

Cleaner and safer water heating options are available, such as ENERGY STAR electric water heaters that generate hot water without burning fuel inside the home.

Switching to an electric heat pump water heater can remove a potential source of carbon monoxide and nitrogen dioxide from your home, and even help reduce ground-level ozone.

Electric heat pump water heaters are also safer to operate with dramatically lower total carbon emissions compared to traditional gas, oil, or propane water heaters.

Regular maintenance is necessary to extend the life of your water heater and ensure it's working efficiently.

Checking the pressure relief valve annually and inspecting gas and water pipes for leaks every year is a good starting point.

Some water heaters, like storage water heaters, may require flushing a quart of water from the tank every few months, and checking the temperature and pressure valves every six months.

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Switching to an electric heat pump water heater can remove a potential source of carbon monoxide (CO) and nitrogen dioxide (NO2) from your home.

These gases can be hazardous to your health and safety, so it's great to have a solution that eliminates them.

Dramatically lower total carbon emissions are another benefit of electric heat pump water heaters, which can also help reduce ground-level ozone, a common environmental problem in many metropolitan areas.

Yes, water heaters do require maintenance to extend their life and ensure they're working efficiently. Routine maintenance is outlined by the manufacturer, but some types may need more attention than others.

Checking the pressure relief valve annually is a good idea, as it prevents excess pressure from building up. You should also check all gas and water pipes for leaks every year.

Flushing a quart of water from the tank every few months is a good maintenance practice for storage water heaters. This helps prevent mineral buildup and keeps the tank clean.

If you have hard water, installing a water softener can help reduce mineral buildup. Some brands also offer anti-scale devices that swirl the water to reduce mineral scale at the bottom of the tank.

For on-demand water heaters, cleaning the filter monthly is a good idea. Periodically descaling the heat exchanger tubes is also recommended.

Solar water heaters require yearly checks for shading to ensure nothing is blocking the solar collectors. You'll also need to replace heat transfer fluids periodically.

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We test heat pump water heaters in a controlled environment to ensure accurate results. Consumer Reports fills each water heater tank with cold water of the same temperature.

We then set the desired temperature to 120°F, which is a common temperature for household use. This allows us to measure how long it takes for each model to reach 120°F.

We measure the time it takes for each model to reach 120°F, providing valuable insights into their performance. This is a crucial factor in determining the overall efficiency of each water heater.

By measuring the wattage, we can determine how much energy each model uses to reach the desired temperature. This information helps consumers make informed decisions when choosing a heat pump water heater.

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Heat pumps are a highly efficient way to heat water, especially in regions with mild winters. They use a built-in heat pump to heat water, and can save more than $5,000 over the life of the unit compared to electric water heaters.

To get the most out of a heat pump water heater, you'll need to consider a few things: air circulation, tank size, condensate drainage, and location. Here are some key considerations:

Geothermal heating is a great alternative to traditional combustion-based heating methods. In countries like Iceland and New Zealand, geothermal heating is a common practice due to their volcanic regions.

Geothermal heating uses the heat from the earth to warm water, making it a highly efficient method. This is especially useful in areas where geothermal activity is prevalent.

In some homes, a wetback stove or heater is used to harness incidental heat from a fireplace or stove. This simple setup can provide a secondary water heating source.

Modern wetbacks may use a more sophisticated design to enhance heat exchange, but these designs are being phased out due to government regulations that don't consider water heating as "efficiently" used.

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Heat pumps can be used for water heating, and they're a game-changer. They use built-in heat pumps to heat water, which can produce lots of hot water and save you more than $5,000 over the life of the unit compared to electric water heaters.

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One of the benefits of heat pump water heaters is that they can save you hundreds of dollars every year on energy costs. In fact, switching to an ENERGY STAR certified heat pump water heater can save you more than $600 per year on your electric bills, compared to a standard electric water heater.

Heat pump water heaters are highly efficient and can be two to four times more energy-efficient than a conventional electric water heater. They're also available in 120-volt models, which can replace gas-fired water heaters without requiring extra electrical work or increased panel capacity.

But heat pump water heaters do require some special considerations. They need open room with a 6’ or higher ceiling, and they require a condensate drain. They also produce condensation, which needs to be routed to a drain or removed by installing a condensate pump.

Some common installation considerations for heat pump water heaters include air circulation, tank size, condensate drainage, and location. For example, most models need about 700 cubic feet of surrounding air space to run at peak performance.

Here are some common pros and cons of heat pump water heaters:

Consider the fuel type, availability, and cost of your water heater, as it affects both annual operation costs and size.

To provide your household with adequate hot water, you need a properly sized water heater.

Examine ways to reduce your hot water use, such as washing clothes in cold water, to save money on your water heating bill.

Here are some key selection criteria to consider:

When selecting a replacement water heater for your home, consider the fuel type, availability, and cost. This will affect the water heater's annual operation costs, as well as its size and energy efficiency.

Fuel types include gas, electric, and heat pump, each with its own set of benefits and drawbacks. For example, gas water heaters can be more energy-efficient than electric ones, but they require a gas line installation.

To provide your household with adequate hot water and maximize efficiency, you need a properly sized water heater. A family of four might use 100 gallons of hot water or more in a day, but that doesn't mean a 100-gallon storage tank is necessary.

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Energy efficiency is another crucial factor to consider. Check the energy efficiency of a water heater before purchasing it, and use the calculator on the government's Energy Saver website to estimate your hot water needs.

The annual operating costs of a water heater can vary significantly depending on its energy efficiency and fuel type. Be sure to estimate these costs and compare them to other models before making a decision.

Here are some key factors to consider when selecting a water heater:

A.O. Smith makes residential and commercial water heaters, boilers, and storage tanks exclusively for plumbing wholesalers and contractors.

General Electric's tank water heaters are available in multiple sizes, with varying levels of warranty coverage and energy-efficiency claims.

Kenmore water heaters are available in multiple sizes, including Power Miser and Hydrosense electronic-temperature-control configurations.

Rheem offers residential water heaters in tank, tankless, and point-of-use configurations, as well as units that work with solar water heating systems.

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Whirlpool tank water heaters are available in multiple sizes, including standard and power vent configurations.

You can find Rheem tankless water heaters at Home Depot, while its tank water heaters are available online and through a network of dealers.

General Electric's GeoSpring electric heat pump water heaters are manufactured in the U.S.

Rheem tank water heaters are available online and through a network of dealers, while Kenmore water heaters can be found at Sears and other retailers.

Whirlpool water heaters are available at Lowe’s, and General Electric's tank water heaters are exclusive to Home Depot.

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High-efficiency condensing units can convert up to 98% of the energy in the fuel to heating the water. This is a significant improvement over older models.

Check valve devices at the inlet and outlet of water heaters help improve efficiency and prevent backflow. This is especially important for fuel-using models.

Electronic ignition in fuel-using models and sealed air intake systems, also known as "band-joist" intake units, have become standard features in modern water heaters. These features help reduce energy waste and improve safety.

Pipe insulation is another important improvement that helps reduce heat loss and save energy. It's a simple yet effective way to make your water heater more efficient.

Residential combustion water heaters manufactured since 2003 in the United States have been redesigned with safety in mind. They now incorporate a thermal cutoff switch to prevent tank overheating due to unusual combustion conditions.

These new designs also feature a flame arrestor screen to prevent vapors from flammable liquids and gases from being ignited. However, it's essential to monitor these screens to ensure they don't become clogged with lint or dust, which can reduce the availability of air for combustion.