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June 13, 2024

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    Radiator heaters are ubiquitous in older homes and new construction alike due to their incredible energy efficiency and cost-effectiveness. Radiators work by heating water with electricity or gas and then pumping it around your home through pipes to baseboard heaters or stand-alone radiator units. They use a combination of convection and radiant heat to keep your home warm.

    Understanding how radiator heaters work is important if you want to learn how to maintain your home’s radiator heating system or if you’re considering purchasing a new system for your home. In this guide, we explain how radiator heaters work, covering the basic operating principles, the different types of radiators, and how to keep your radiators functioning smoothly.

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    • Radiators are common home heating devices that use hot water to heat your home.
    • A central boiler produces steam or hot water that then travels through pipes throughout your home.
    • Radiators are generally highly efficient, easy to maintain, and pose virtually zero health risks.

    What Is a Radiator Heater?

    Radiator heaters are a family of home heating devices that use hot water or steam to heat your home through a combination of radiation and convection. They are one of the oldest forms of indoor heating and remain popular today because they are relatively inexpensive to maintain, efficient, and already installed in many homes and buildings.

    Radiators rely on a boiler or water heater to create steam or hot water that subsequently gets pumped throughout your home via a network of pipes. When the steam or hot water enters the radiator, it heats up a series of fins or coils that, in turn, heat the air around the radiator, heating your home.

    Here’s a breakdown of the key components that make up a radiator heater:

    • Boiler/water heater: Hot water or steam boilers produce steam or hot water that can then be circulated throughout your house to your radiators.
    • Fins and coils: These components increase your radiator’s surface area, allowing it to transfer more heat to the surrounding air.
    • Pipes: The hot water or steam in your radiator travels through a network of pipes to heat individual rooms in your home.
    • Radiator valves: Valves control the flow of hot water and steam into and out of your radiators.
    • Thermostat: Radiator heaters are usually connected to a thermostat so they can detect when they need to run automatically.

    How Radiator Heaters Work

    Let’s take a closer look at how radiators work so you can better understand their advantages and disadvantages.

    Radiator heating systems depend on a centralized boiler or water heater to produce steam or hot water that travels throughout your home via pipes to your baseboard heaters or stand-alone radiator units. The heat from the pipes radiates to increase the temperature of the air surrounding the radiator, which then circulates throughout your home via convection.

    While a pipe full of hot water or steam will feel incredibly hot to the touch, it’s not very good at transferring that heat to the air in your home. A key design element of radiators is a set of fins or coils that serve to increase the surface area of hot material that makes contact with the air. These fins or coils are generally made of a metal with a high heat conductivity to increase your heating system’s overall efficiency and reduce the amount of time it takes your home to heat up.

    The primary heating loop for radiator heaters works like this:

    • Water is heated. A centralized boiler heats water to produce either steam or hot water, depending on the type of radiator system you have.
    • The thermostat detects temperature changes. When your thermostat senses that your home needs to be heated, it triggers a circulator to pump hot water through your home if you have a hot water radiator. If you have a steam radiator, the thermostat opens a valve that releases steam so it can flow freely to your radiator unit.
    • The air around the radiator heats up. As the steam or water flows through the system, it loses heat and transfers it to the radiator fins and coils, heating up the air in the room. The condensed steam or cooled water returns to the boiler via a return pipe, where it can be reheated and reused.
    • The system turns off, and the water reheats. Once your thermostat detects that your home has reached the desired room temperature, the circulator is turned off, or the steam valve is closed. The water in the boiler is continuously reheated as needed, so it’s ready to use again.

    All radiators need either hot water or steam to function, but how they get that hot water or steam varies. The following sections summarize three of the most popular radiator designs: hot water radiators, steam radiators, and radiators with electric water heaters.

    Below is a video detailing how steam radiator heaters work. The principles in the video are similar to how baseboard heaters work as well:

    How Do Hot Water Radiators Work?

    Hot water radiators use a water boiler to heat water to near-boiling — usually around 180°F — and circulate it throughout your home when your home needs to be heated. An inlet allows hot water to enter the system from the boiler, and an outlet allows it to leave the system and return to the boiler’s water tank, where it can be reheated.

    Hot water radiators require a circulator or pump to transport hot water throughout your home, making them slightly more prone to malfunctions than steam radiators since they have an extra component that may break down.

    How Do Steam Radiators Work?

    Steam radiators function similarly to hot water radiators, but they don’t use a pump. Instead, a set of valves controls when steam is allowed to flow through the system. The valves open when your home needs to be heated and close once it reaches the desired temperature. The main advantage of steam radiators vs. hot water radiators is that they don’t need a pump since steam naturally flows from high pressure to low pressure.

    As the steam flows through the radiator, it loses heat, eventually condensing to water and flowing back to the boiler through a return pipe.

    How Do Electric Water Heaters Work?

    Not all hot water systems heat their water the same way. Electric water heaters use electricity to raise the temperature of a heating element inside the system’s water tank. The heating element transfers heat to the water, raising its temperature so it can flow through the system and heat your home.

    Electric water heaters are typically more efficient and cheaper to run than traditional oil or gas-based water heaters. They’re especially economical when paired with solar panels since you can use the power generated by your panels to heat your home. Even if your solar system doesn’t generate enough power to run your heating system entirely, it can still greatly reduce your monthly heating bill.

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    What Are the Benefits of Radiator Heaters?

    Radiators are still one of the most popular home heating options, even as forced air systems become more prevalent. A properly cared-for radiator is highly efficient, easy to maintain, and poses virtually zero health risks. Here is a more detailed look at the main benefits of radiator heaters:

    • Comfort and warmth. Radiators are great at maintaining temperature, but they also take a little time to warm up, literally. However, once your home reaches the temperature you want, radiators are very good at keeping it there. Having good airflow can help radiators heat your home more effectively without the need for blowers to help the warm air circulate.
    • Cost-effectiveness. Since radiators are so efficient, they’re also very cost-effective and will help you save money compared to other home heating options. All of the money you spend on your gas, oil, or electric bill to heat the water for your radiator heater gets converted directly to heat output for heating your home, with virtually zero heat loss. Additionally, radiators are easy to maintain and require very little professional maintenance.
    • Durability. Radiators are resilient systems with relatively few moving parts and maintenance requirements. Bleeding your radiators to remove air from the line is important, and routine checks on your system’s circulator and water heater are required, but you shouldn’t run into many durability-related issues.
    • Energy efficiency. Hot water and steam radiators are the most efficient way to heat your home and are far more efficient than central heating or electric radiators. Since radiators are closed systems, they can get extremely close to 100% efficiency, with very little energy wasted and nearly all of it going toward heating your home. Maintaining high energy efficiency requires regular maintenance but is relatively straightforward.
    • Safety. Radiators are safer than forced air heating systems since you don’t have to worry about breathing in mold or mildew if you don’t clean your vents regularly. You should make sure the surface temperature of your radiator is set to a safe level to avoid contact burns. You can adjust the intake and outlet valves yourself or have them set by a professional during an inspection.

    Radiator Heater Maintenance

    Radiator heaters are relatively low-maintenance compared to other heating systems, but they still require a bit of attention to keep them running smoothly.

    If your hot water radiators are taking longer than normal to heat up or if they’re making unusual gurgling sounds, it could be time to bleed them. Bleeding your radiators is fairly straightforward and shouldn’t take much time. Use the bleed key your radiator came with to turn the bleed valve counterclockwise until you hear a hissing sound. Close the valve as soon as the water starts escaping instead of air.

    Steam radiators can become clogged over time if you don’t clean out their air vents. Clogged vents make your radiator less efficient and effective, which wastes money and makes it harder to keep your home comfortable during the winter. You can use a thin wire, needle, or other hard, narrow object to clean any gunk out of the air hole.

    You should also inspect your radiator’s pipes once per year to make sure they’re still in good shape. Pipes wear out over time, and small cracks or pinholes can turn into big problems quickly if they’re not taken care of. A quick visual inspection is enough to catch most problems, but you can ask a plumber to check during a routine visit if you want to be extra careful.

    Today’s Homeowner Tips

    Most radiators don’t require regular visits from a professional, but it can be helpful to have your burner and circulator inspected to stay ahead of potential problems. Many companies recommend yearly inspections, which is a good option if you don’t want to spend the time inspecting your radiators yourself.

    Our Recommendation on Radiators

    Understanding how radiators work makes it easier to diagnose problems when they crop up so you can keep your home nice and toasty during the winter. We hope you’ve found this guide helpful for learning how radiators operate and now have a better idea of whether a radiator heating system is the right choice for your home. Radiators are efficient, cost-effective, and easy to maintain, making them a great choice for most homeowners.

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    FAQs About Radiator Heaters

    How long do radiator heaters last?

    Home heating radiators usually last between 15 and 20 years, depending on the type of heater you have and the level of care it’s given throughout its life. With regular bleeding and routine checkups to inspect the circulator and water boiler, you can easily get 20 years out of a radiator heater.

    Are radiator heaters safe?

    Radiator heaters are very safe, especially compared to forced air systems that can cause respiratory illness from mold and bacteria. The primary concern with radiator heaters is the dry air they create in your home, which can lead to minor problems like dry skin and a scratchy throat. Radiators can also cause burns if they’re not calibrated correctly, so make sure to have a professional set the contact temperature during a routine maintenance visit.

    Radiators are also much safer than electric space heaters, which are a common cause of household fires.

    Can radiator heaters make you sick?

    Radiator heaters are not likely to make you sick since they are closed systems. Home heating options that use ducts to pump air throughout your room can cause respiratory problems if you don’t have them cleaned regularly. Radiators don’t have the same problem and are generally considered much safer.

    How often should you bleed your radiator?

    Experts recommend bleeding your radiators at least once per year, preferably well before the winter months when the system will see heavy use. It can be a good idea to bleed your radiators more frequently if you notice they’re taking longer to heat up or if they’re making a lot of noise when they turn on.

    What is a Lockshield Valve?

    A lockshield valve is a type of valve used on radiators to balance the flow of hot water through the system. It is typically located on the opposite end of the radiator from the thermostatic radiator valve (TRV) and is covered by a plastic cap that requires a special key or tool to adjust, which stops you from accidentally changing the setting.

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    Reviewed for accuracy, cost data, industry best practices, and expert advice by Jonathon Jachura.
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    Dan Simms


    Dan Simms worked in real estate management for five years before using his experience to help property owners maintain their own homes. He got his master’s degree in English Literature and Creative Writing, and he now enjoys sharing his knowledge about homeownership and DIY projects with others on Today’s Homeowner. When he’s not writing, he’s usually outdoors with his wife and his dog, enjoying mountain biking, skiing, and hiking.

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    Jonathon Jachura


    Jonathon Jachura is a two-time homeowner with hands-on experience with HVAC, gutters, plumbing, lawn care, pest control, and other aspects of owning a home. He is passionate about home maintenance and finding the best services. His main goal is to educate others with crisp, concise descriptions that any homeowner can use. Jon uses his strong technical background to create engaging, easy-to-read, and informative guides. He does most of his home and lawn projects himself but hires professional companies for the “big things.” He knows what goes into finding the best service providers and contractors. Jon studied mechanical engineering at Purdue University in Indiana and worked in the HVAC industry for 12 years. Between his various home improvement projects, he enjoys the outdoors, a good cup of coffee, and spending time with his family.

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