Types of Water Heaters
Selecting a New Water Heater
You have a lot to consider when selecting a new water heater for your home. You should choose a water heating system that will not only provide enough hot water but will also do so energy efficiently and save you money. This includes considering the different types of water heaters available and determining the right size and fuel source for your home.
It's a good idea to know the different types of water heaters available before you purchase one:
- Conventional storage water heaters: Offer a ready reservoir (storage tank) of hot water
- Demand (tankless or instantaneous) water heaters: Heat water directly without the use of a storage tank
- Heat pump water heaters: Move heat from one place to another instead of generating heat directly for providing hot water
- Solar water heaters: Use the sun's heat to provide hot water
When selecting the best type and model of water heater for your home, consider the following:
- Fuel type, availability, and cost. The fuel type or energy source you use for water heating will not only affect the water heater's annual operation costs but also its size and energy efficiency.
- Size. To provide your household with enough hot water and to maximize efficiency, you need a properly sized water heater.
- Energy efficiency. To maximize your energy and cost savings, you want to know how energy efficient a water heater is before you purchase it.
- Costs. Before you purchase a water heater, it's also a good idea to estimate its annual operating costs and compare those costs with other less or more energy-efficient models.
Also, be sure to do what you can to reduce your hot water use. You may also want to explore other strategies such as drain-water heat recovery to save money on your water heating bill.
Fuel Types, Availability, and Costs for Water Heating
When selecting a new water heater, it's important to consider what fuel type or energy source you will use, including its availability and cost. The fuel used by a water heating system will not only affect annual operation costs but also the water heater's size and energy efficiency.
Exploring Water Heater Options by Fuel Type
Fuel type and its availability in your area may narrow your water heater choices.
The following is a list of water heater options by fuel or energy source:
- Electricity: Widely available in the United States to fuel conventional storage, tankless or demand-type, and heat-pump water heaters. It also can be used with combination water and space heating systems, which include tankless coil and indirect water heaters.
- Fuel oil: Available in some areas of the United States to fuel conventional storage water heaters and indirect combination water and space heating systems
- Geothermal energy: Available throughout the United States to those who will have or already have a geothermal heat pump system installed in their homes for space heating and cooling
- Natural gas: Available in many areas of the United States to fuel conventional storage and demand (tankless or instantaneous) water heaters, as well as combination water and space heating systems, which include tankless coil and indirect water heaters
- Propane: Available in many areas of the United States to fuel conventional storage and demand (tankless or instantaneous) water heaters, as well as indirect combination water and space heating systems
- Solar energy: Available throughout the United States—most abundantly in the Southwest—for solar water heaters
Comparing Fuel Costs and Water Heater Types
If you have more than one fuel type available in your area, it's a good idea to compare fuel costs, especially if you're building a new home. Even if you're replacing a water heater, you may find that you'll save more money in the long run if you use a different fuel or energy source. Contact your utility provider for current fuel costs or rates.
The type of water heater you choose will also affect your water heating costs. One type of water heater may use a fuel type more efficiently than another type of water heater. For example, an electric heat pump water heater typically is more energy efficient than an electric conventional storage water heater. Also, an electric heat pump water heater might have lower energy costs because of its higher efficiency than a gas-fired conventional storage water heater, even though local natural gas costs might be lower than the electricity rates.
Conventional Storage Water Heaters
Conventional storage water heaters remain the most popular type of water heating system for the home.
How They Work
A single-family storage water heater offers a ready reservoir— from 20 to 80 gallons—of hot water. It operates by releasing hot water from the top of the tank when you turn on the hot water tap. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full.
Conventional storage water heater fuel sources include natural gas, propane, fuel oil, and electricity.
Since water is constantly heated in the tank, energy can be wasted even when a hot water tap isn't running. This is called standby heat loss. Only tankless water heaters—such as demand-type water heaters and tankless coil water heaters—avoid standby heat losses. Some storage water heater models have heavily insulated tanks, which significantly reduce standby heat losses and lower annual operating costs. Look for models with tanks that have a thermal resistance (R-Value) of R-12 to R-25.
Gas and oil water heaters also have venting-related energy losses. Two types of water heaters—a fan-assisted gas water heater and an atmospheric sealed-combustion water heater—reduce these losses.
You may also want to consider some less conventional storage water heaters—heat pump water heaters and solar water heaters. These water heaters are usually more expensive, but they typically have lower annual operating costs.
Selecting a Storage Water Heater
The lowest-priced storage water heater may be the most expensive to operate and maintain over its lifetime. While an oversized unit may be alluring, it carries a higher purchase price and increased energy costs due to higher standby energy losses.
Before buying a new storage water heater, consider the following:
- Size and first hour rating
- Fuel type and availability
- Energy efficiency and costs
Installation and Maintenance
Proper installation and maintenance of your water heater can optimize its energy efficiency.
Proper installation depends on many factors. These factors include fuel type, climate, local building code requirements, and safety issues, especially concerning the combustion of gas- and oil-fired water heaters. Therefore, it's best to have a qualified plumbing and heating contractor install your storage water heater.
Be sure to do the following when selecting a contractor:
- Request cost estimates in writing
- Ask for references
- Check the company with your local Better Business Bureau
- See if the company will obtain a local permit if necessary and understands local building codes, etc.
Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency.
Routine maintenance for storage water heaters, depending on what type/model you have, may include:
- Flushing a quart of water from the storage tank every three months
- Checking the temperature and pressure valve every six months
- Inspecting the anode rod every three to four years
Heat Pump Water Heaters
Most homeowners who have heat pumps use them to heat and cool their homes. But a heat pump also can be used to heat water—either as a stand-alone water heating system, or as a combination water heating and space conditioning system.
How They Work
Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. Therefore, they can be two to three times more energy efficient than conventional electric resistance water heaters. To move the heat, heat pumps work like a refrigerator in reverse.
While a refrigerator pulls heat from inside a box and dumps it into the surrounding room, a stand-alone air-source heat pump water heater pulls heat from the surrounding air and dumps it—at a higher temperature—into a tank to heat water. You can purchase a stand-alone heat pump water heating system as an integrated unit with a built-in water storage tank and back-up resistance heating elements. You can also retrofit a heat pump to work with an existing conventional storage water heater.
Heat pump water heaters require installation in locations that remain in the 40º–90ºF (4.4º–32.2ºC) range year-round and provide at least 1,000 cubic feet (28.3 cubic meters) of air space around the water heater. Cool exhaust air can be exhausted to the room or outdoors. Install them in a space with excess heat, such as a furnace room. Heat pump water heaters will not operate efficiently in a cold space. They tend to cool the spaces they are in. You can also install an air-source heat pump system that combines heating, cooling, and water heating. These combination systems pull their heat indoors from the outdoor air in the winter and from the indoor air in the summer. Because they remove heat from the air, any type of air-source heat pump system works more efficiently in a warm climate.
Homeowners primarily install geothermal heat pumps—which draw heat from the ground during the winter and from the indoor air during the summer—for heating and cooling their homes. For water heating, you can add a desuperheater to a geothermal heat pump system. A desuperheater is a small, auxiliary heat exchanger that uses superheated gases from the heat pump's compressor to heat water. This hot water then circulates through a pipe to the home's storage water heater tank.
Desuperheaters are also available for tankless or demand-type water heaters. In the summer, the desuperheater uses the excess heat that would otherwise be expelled to the ground. Therefore, when the geothermal heat pump runs frequently during the summer, it can heat all of your water.
During the fall, winter, and spring—when the desuperheater isn't producing as much excess heat—you'll need to rely more on your storage or demand water heater to heat the water. Some manufacturers also offer triple-function geothermal heat pump systems, which provide heating, cooling, and hot water. They use a separate heat exchanger to meet all of a household's hot water needs.
Selecting a Heat Pump Water Heater
Heat pump water heater systems typically have higher initial costs than conventional storage water heaters. However, they have lower operating costs, which can offset their higher purchase and installation prices.
Before buying a heat pump water heating system, you also need to consider the following:
- Size and first hour rating
- Fuel type and availability
- Energy efficiency (energy factor)
- Overall costs
Installation and Maintenance
Proper installation and maintenance of your heat pump water heating system can optimize its energy efficiency.
Proper installation depends on many factors. These factors include fuel type, climate, local building code requirements, and safety issues. Therefore, it's best to have a qualified plumbing and heating contractor (or geothermal heat pump system installer/designer) install your heat pump.