New boiler installed upstairs

What’s the difference between a vented and an unvented cylinder?

When it comes to having your heating and hot water system replaced or upgraded, you may well be considering a new cylinder. In this article, we look at the differences between vented and unvented cylinders and what it means for you as a homeowner.

What is a vented cylinder?

Most homes with hot water cylinders typically have a vented cylinder. It is usually made from copper and gets its water supply from a large cold water cistern tank located in the loft space. The boiler obtains its water supply by way of a gravity feed from the tank to the cylinder. A vented cylinder gets its name from a vent pipe which terminates into the tank in the loft and allows for expansion as the water is heated.

What is an unvented cylinder?

In contrast to a vented cylinder, an unvented cylinder is fed directly from the cold mains supply. This means that there is no need for a tank in the loft space. Thanks to their direct feed from the cold mains supply, they benefit from improved pressure and flow rate. Instead of a vent pipe, unvented cylinders have an expansion vessel or an internal air gap within the cylinder to allow for expansion as the water is heated.

Should I choose a vented cylinder or an unvented cylinder?

There are two ways to heat vented and unvented cylinders - either via a boiler (indirect) or with an immersion heater (direct). There are, however, advantages and disadvantages to consider when choosing a vented or unvented cylinder.

Vented Cylinder

Advantages Disadvantages
  • Cheaper to install & maintain
  • Good in low water pressure areas
  • Gravity-fed, which can result in poor hot water flow upstairs
  • Takes up more space with tanks in loft space

Unvented Cylinder

Advantages Disadvantages
  • No tanks required means more flexibility for where it can be installed
  • Better flow and pressure thanks to direct feed from the cold mains
  • No tanks required, meaning more space in your loft (ideal if you are planning a loft conversion)
  • Higher cost of installation
  • If cold main supply is shut off, there will be no hot water
  • Maintenance can be more expensive

Which is the best cylinder for me?

When choosing the best option for your home, you should consider the above advantages and disadvantages, as well as some other important factors. Let’s take a closer look at some key questions.

How strong is your cold water main?

This is often the number one factor in deciding which cylinder to have installed in your property. Most unvented hot water cylinders require a cold water mains pressure of 1.5bar and a flow rate of no less than 20 litres per minute. If this cannot be achieved, then a vented cylinder will generally be recommended. If your home requires a vented cylinder, it is possible to fit a shower boost pump which will increase the flow and pressure to your shower or bath if required.

What is your current heating system?

Most cylinders run off a conventional boiler or a system boiler. These boilers heat the water via a coil within the cylinder when needed. If you are changing from a vented cylinder to an unvented cylinder, one thing to bear in mind is that an unvented cylinder may run at a far higher pressure than your existing pipework can handle.

How big is your house?

A hot water cylinder is generally recommended to cope with the hot water requirements of larger homes with more than one bathroom. This will, however, require sufficient upstairs space for the cylinder and enough height in the loft space to produce the gravity that the system requires.

A vented cylinder may be the better option If you have 2 or more bathrooms as the cold water storage cistern is able to supply multiple outlets at the same time without any effect on the pressure. An unvented cylinder, on the other hand, relies on the cold mains. If too many outlets are operated at the same time, the flow will weaken. It is worth noting that this is generally only a problem for homes with three or more bathrooms that are likely to be in use at the same time.

Understand your options better with a free quotation

Still not sure whether you should choose a vented or an unvented cylinder? We will be happy to explain all the options available and provide you with a free quotation. Call us today on Wrexham 01978 291 923 or Mold 01352 620 125.

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