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How do Boilers Work?

Explanations to understand some difficult concepts about boilers

Date published: 31 August 2012

Understanding the way a boiler works is not as difficult as it may seem at the beginning. The aim of this article is to make it easier for you to understand how a boiler works and to clarify some of the more difficult concepts to grasp. Understanding how a boiler works will allow you to make the right choice when you decide to buy a new boiler. Equally, if you have plumbing problems and you call a plumber to fix the problem, it will make the plumber’s explanations a lot clearer.

Definition

In spite of its name, water is not boiled inside a boiler. A boiler is indeed an appliance used to supply central heating and/or to provide hot water for taps and showers. The water is heated until the required temperature is achieved and then the heat source turns itself off.

What energy are boilers based on?

There are 4 types of fuel that can be used for a boiler:

- Solid fuel
- Electricity
- Gas
- Oil

Electric boilers are usually found in all-electric buildings such as blocks of flats, while solid fuel boilers are more labour intensive as they require loading up the fuel and emptying the ash. According to Treloar's “Master Basic Plumbing and Central Heating” (2010: p. 94), most boilers in the UK use gas, while the rest use oil. Treloar argues that it may be up to 92% of people in the UK use gas, while the rest use oil.

Types of Boiler Designs

1. Combination vs. System Boilers

A combination boiler has become the standard nowadays, due to their compact size. A combination boiler in contrast to a system boiler eliminates the need for storing hot water. Therefore, you will no longer need a hot water cylinder. A combination boiler will also allow you to save some money on hot water costs and will deliver water at the mains pressure. The flow however will be limited if several taps will be running at the same time. The only problem with combi boilers revolves around potentially the size of your house. If your house is too big, a boiler may not be sufficient to heat up the entire house. To complement this section, I also found this useful article about how combination boilers work.

System boilers, sometimes also called sealed system boilers, provide central heating through a storage cylinder. Therefore, a system boiler works on the principle of stored hot water. The hot water is pumped from the boiler through the system, which results in a fast and economical running. The benefit with system boilers is that they have the power to heat up bigger houses and in addition, they do not need feeds and expansion cistern.

TradePlumbing offers a great variety of both combi boilers and system boilers at affordable prices.

2. Condensing vs. Non-condensing boilers

A condensing boiler is also known as a high-efficiency boiler or a combi boiler and in contrast to non-condensing boilers, there is some consideration for heat, which is present in the combustion products and which are removed from the boiler. Condensing boilers are designed so that combustion products are cooled off and therefore, the heating energy of such products can be reused. These boilers can extract the extra heat by using the larger and more tightly grouped heat exchanger.

In contrast to boilers, which were installed 30 years ago and which operate at 50 or 60% efficiency, new boilers can operate at an efficiency of more the 90%. Essentially, boiler efficiency will have a direct impact on you gas bill. So, if your boiler is 50% efficient, that means that for every £100, you will only be getting £50 worth of heat, which means that the rest will be wasted up the chimney. In contrast, a boiler, which is 90% efficient, will allow you to get £90-worth of heat for every £100 that you spend. Nowadays, you would not even be able to install a boiler with an efficiency lower than 86%. The law requires that you install a boiler which has an efficiency of more than 86%.

3. Room-sealed vs. Open-flued

There are many different types of boiler designs, with subsidiary features and characteristics depending on the manufacturer. Boiler designs may feature natural or forced draught, which indicate the type of ventilation, which is used in order to get rid of the combustion products. If the boiler takes the air from within the room where the boiler is located, that will be an open-flued boiler. If the boiler takes the air from outside the building, that will be a room-sealed boiler.

These types of boilers are available:

- Natural draught room-sealed
- Forced draught room-sealed (fan-assisted)
- Natural draught open-flued
- Forced draught open-flued (fan assisted)

If you are not sure which type of boiler you have, there are two things to indicate whether you have an open-flued or room-flued boiler. A draught open-flued boiler will be usually placed in a kitchen, having a pipe emerging from the top, going to the chimney and going through a discharging pipe above the roof. If your boiler is placed behind a gas fire, then you are likely to have a draught open-flued boiler.

The list of criteria for distinguishing between boilers is not exhaustive, but it does help in understanding some of the more difficult concepts such as room-sealed vs. open-flued, condensing vs. non-condensing and combination vs. systems boilers. Of course, there are additional criteria to distinguish between boilers like size, capacity, or power. However, these are more straightforward concepts, which are easier to understand. To complement the information in this article, I also recommend this article on understanding your system from Energy Saving Trust.

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