What is a heat exchanger in a boiler?
You may take it for granted that your boiler is able to heat water up and then deliver it around your home, either through your radiators or to your taps. You might not, however, have thought about how it achieves this.
The heat exchanger is the key. Without this device, your boiler wouldn’t be able to warm up your water. So what exactly is a heat exchanger and how does it work in your boiler? In this helpful article, we’ve answered all of your questions around the position and location of your gas boiler and whether it can be moved.
What is a heat exchanger in a boiler?
A heat exchanger within a heating system allows heat to be passed between two liquids or gases without allowing the substances to mix together. For instance, hot water or hot gas can be used to heat a separate chamber of water or gas.
Within the heat exchanger is a long, coiled pipe that is surrounded by the substance to be heated, such as cold water. A hot substance, such as gas or water, is fed through the pipe and, as it moves, it gradually heats the surrounding water. A heat exchanger doesn’t allow these two substances to combine, as this wouldn’t work as effectively - the water can be heated up much faster than if hot water was simply added to cold water.
While heat exchangers are commonly found in heating appliances, such as a boiler, they can be found in tons of other applications and industries too. They can heat swimming pools or recycle the heat created by an engine, such as in a bus or aeroplane, and use it to warm up the cabin where the passengers are located, reducing the need for a separate heater.
Additionally, these clever components work in the opposite way. Just as they can apply heat to a gas or liquid, they can also be used to remove heat. Refrigerators and air conditioners contain heat exchangers to keep a space cool.
Heat exchangers are most commonly found in boilers. They allow your boiler to heat the water that is then pumped through your radiators to warm your home. Without it, your boiler wouldn’t be much use at all, making it a really important aspect of your heating system. Let’s take a closer look at how a heat exchanger works in your home’s combi boiler.
How does a combi boiler heat exchanger work?
A boiler works by using hot gas to heat water, and a heat exchanger is what allows this to happen.
As the gas is heated, it begins to rise. When it rises, it reaches the heat exchanger and is pushed through the coiled pipe. The cold water that surrounds the pipe is heated as the hot gas moves through the system, and is ready to be pumped to your home’s radiators and taps.
The two main types of gas boilers, condensing and non-condensing, both contain a heat exchanger, however you can no longer have a new non-condensing boiler fitted in your home as it’s not considered efficient enough.
The efficiency of a non-condensing boiler is generally lower as it doesn’t reuse the hot waste gases to further heat the water in the system. These waste gases can reach a high temperature of up to 250 °C and so have the ability to be recycled and used to further heat cold water. In comparison, a condensing gas boiler is able to use these gases for ultimate efficiency.
Condensing gas combi boilers used to have two heat exchangers, as it’s thought that this was more efficient. To begin with, the water was heated in the primary exchanger. As hot waste gases were produced, the water that returned from its circuit around the radiators was pushed into the secondary heat exchanger, which only used waste gas to heat the water. Once it had been heated slightly in this heat exchanger, it returned to the primary one to become even hotter.
Viessmann boilers only contain one heat exchanger. The stainless steel design means that all of the heat generated can be extracted in one pass. This is due to the exchanger’s larger surface area and the position of the burner, which sits centrally within the cylindrical heat exchanger.
The water in the heating system can’t retain its heat forever. As it moves through your radiators or sits unused in a water tank, it’ll gradually cool down. Once it has cooled too much, it gets pumped back to the boiler for the heat exchanger to warm the water again (unless the programme is turned off). If the boiler determines that the water is still an acceptable temperature, it will be pumped around your radiators again.
What boilers have stainless steel heat exchangers?
For a heat exchanger to have a long lifespan and live for the same duration as your boiler, it should be made out of a strong material such as stainless steel.
Stainless steel is the ideal material because it resists corrosion, is able to withstand a high flow rate, is lightweight and is self-cleaning. All of these mean the boiler will last longer and maintain its efficiency over a prolonged period of time too.
A higher flow rate allows water or gas to pass through at a faster rate, so the water in your heating system can be heated more quickly, and with the reduced risk of blockages caused by debris, rust or limescale.
All of Viessmann’s condensing boilers have stainless steel heat exchangers so you can be assured that your boiler will run at maximum efficiency.
How to clean a boiler heat exchanger
As with any water-based system, rust and limescale can begin to clog the pipes, leading to reduced efficiency. Even when a heat exchanger is made from stainless steel, which resists rust, it may require some cleaning every now and then. Signs that your system may need cleaning include radiators that are cold at the bottom.
You should contact a suitably qualified heating engineer who will be able to clean the heat exchanger for you. If you’d prefer, you can ask them to do this during your boiler’s annual service. The engineer will locate the exchanger and apply water at high pressure to blast out any dirt or debris, and also examine the heat exchanger for damage. You should make sure that this task is done every 12 months to keep your boiler working at its most efficient for longer.
