Is a Boiler the Same as a Water Heater?

Today we thought we’d clear up a fairly common confusion many people have about boilers and how they are related to water heaters. Both boilers and water heaters serve a similar purpose in providing hot water, but the two units aren’t the same thing. A water heater works to provide hot water for cleaning, showering, laundry, etc., whereas a boiler provides hot water that is used to heat the building. That being said, there is a type of combination boiler that also serves as a water heater at the same time.

Differences Between Boilers and Water Heaters

One of the main differences between a boiler and a water heater is that the water heater is designed to produce potable water, which means that it is safe to drink. The hot water produced by most boilers is definitely not safe to drink. The reason is that boilers usually recirculate water through the radiators or underfloor heating and then back into the boiler instead of constantly replenishing the system with new clean water as a water heater does. This means that the water coming out of a boiler will usually be quite old and stale.

Another difference is that boilers usually heat the water to a much higher temperature. Most units don’t actually heat the water until it is boiling and instead only heat it to around 190 degrees. However, there are some boilers that are designed for use with baseboard radiators that use a combination of heat and pressure to turn the water into steam.

Water heaters are designed so that the water should never be able to get that hot to reduce the potential risk of scalding. Most water heaters will never heat above 160 degrees Fahrenheit, and all traditional water heaters also have a relief valve that will automatically activate if the water inside the tank ever gets too hot.

How Boilers Work

Traditional boilers are large units that have two large storage tanks, one for hot water and one for cold water. These units most commonly run off natural gas, but you can also find oil, propane and electric units as well. The boiler is controlled by a thermostat, which signals the boiler to turn on whenever the indoor temperature drops and heat is needed.

The boiler then instantly starts heating the water in the hot tank, and the hot water is then pumped out into the radiators or out through pipes under the floor, depending on the specific type of radiant heating system. This process forces the cold water that was sitting inside the radiators or pipes back towards the boiler and into the cold-water tank. The process is a closed loop, which means that water flows out of the hot water tank, through the heating system and then back into the cold-water tank whenever the boiler is heating. The water in the cold tank is then used to replenish the hot water tank as well.

The fact that the system is closed loop means that there is no way that this type of boiler can also provide hot water for your plumbing. As a result, homes with a radiant heating system that uses a traditional boiler also have to have a separate water heater. The only way to avoid this is to use a combination boiler water heater, more commonly known as a combi-boiler.

How Water Heaters Work

Traditional water heaters work in much the same way as traditional boilers. These units use either gas or electricity to heat the water inside a large storage tank. An outlet pipe connects to the tank that supplies hot water to all of the building’s plumbing fixtures.

The difference between this process and that of a boiler is that the system is not a closed loop. Instead, fresh cold water is constantly drawn into the tank any time any hot water is used. This cold water flows through a long pipe into the bottom of the tank so that it can quickly be heated and also doesn’t mix with the hot water at the very top of the tank where the outlet pipe is located.

Tankless water heaters are different from traditional units as they don’t have a storage tank and instead only start heating when you turn the hot water on somewhere in the building. These units can also use either gas or electricity for heating.

Gas units have a combustion chamber where flames are created to produce hot fumes. These fumes then travel through a metal heat exchanger, and the process almost instantly causes the metal to become extremely hot. As water flows over the heat exchanger, the heat energy is released and raises the water temperature.

Electric units have an electric resistance coil that is located inside a heat exchanger. Electricity flows through the coil and causes it to become glowing hot, which heats the exchanger so that it can, in turn, heat the water.

Although both gas and electric tankless units heat extremely efficiently and quite quickly, there can still be a lag time of anywhere from 15 seconds to a minute or two before the hot water starts flowing out of the fixture. The amount of lag time depends on how far away the fixture is from the water heater and also how cold the water is coming into the unit.

Indirect Water Heaters

Indirect water heaters don’t have any type of heating element. Instead, these units rely on the heat produced by a boiler to keep the water inside their storage tank hot. A pipe is connected from the boiler to the water heater. This pipe has several coils that run inside the water heater tank, and the pipe then connects in a loop back to the boiler. Whenever the unit needs to heat, hot water runs through the pipe to heat the water inside the tank and then back out into the boiler tank.

Combination Boiler Water Heaters

Combination boiler water heaters are designed to provide hot water for both plumbing and radiant heating. These units are essentially the same as a tankless water heater, but they are typically slightly larger and more powerful as they often need to supply more hot water at a time or heat it to a higher temperature for the radiant heating system.

These units will always prioritize your plumbing to ensure that you quickly have access to hot water whenever you open your faucet or turn on the shower. In this situation, the water coming out of the mainline passes through a heat exchanger and into your plumbing system. When providing hot water for radiant heating, the water is circulated through the same type of closed-loop system as with any other type of boiler.

If you have any issues with either a water heater or a boiler, Southport Home Services has got you covered. We offer a full range of water heater services as we also install and repair boilers and radiant heating systems. We also work on sump pumps and offer drain cleaning as well as plumbing repairs and installations. If you need any other heating or cooling installation, repair or maintenance service, we can help with that as well. If you need any residential or commercial plumbing or HVAC service in Wausau, give Southport Home Services a call today.

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Thomas Suchla
Thomas Suchla


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