Radiators – your one stop guide!

We get tons of questions from our customers regarding radiators: when to change them, when to flush them, how to bleed them and so forth – so here we have produced a one stop guide to radiators and all the important things you need to know.

Bleeding your radiators

What is it and why do you need to do it?

Bleeding is where you vent trapped air from the radiator, which can build up over time and prevent your radiators from working correctly. Small amounts of air enter the central heating system every time fresh mains water flows through the boiler/heating system. This air collects at the top of the radiators, preventing the top part of the radiator filling with warm water and therefore reducing its heating capability.

It is important to bleed your radiators on a regular basis, since releasing this trapped air can dramatically improve the efficiency of your central heating. It is a simple job that you can do yourself with a bit of knowhow, however if you have any problems or you are unsure how to proceed, it is worth getting a plumber to do this for you.

How do you know if your radiator needs bleeding?

The best way to check is to turn your heating on and wait for the radiators to warm up. If there are any cool spots, especially near the top of the radiator, you may need to bleed it. If the radiator doesn’t warm up at all, then potentially it is completely full of air and so this will need to be released before it can be used to heat rooms.

How do I bleed my radiator?

Firstly ensure your heating is off – you don’t want to burn yourself with hot water!

Radiator Key

You will then need a radiator bleeding key, or a flat headed screwdriver for more modern systems. At the top of the radiator at one end you will find a valve where you can put the key or screwdriver. Make sure you have a cloth ready to catch any drips!

Then slowly turn the valve anti-clockwise. You should start to hear gas escaping with a hissing sound. Eventually the gas will all be gone and liquid will start to escape. You then need to close the valve as quickly as possible to stop too much water escaping and making a mess.

The last step after bleeding all your radiators with cold spots is to check the pressure of the system. If you have bled a lot of gas, the pressure in the system may be low and in this instance you will need to top it up using the ‘filling loop’, which is a little lever on your boiler.

The final check is to turn your heating back on and just confirm that the cold spots have disappeared.

You should also try balancing your radiators.

Flushing radiators

Flushing your radiators is a job carried out by professionals and involves completely cleaning them out and gets rid of any sludge that has built up over the years. It is definitely worth doing and you may find the improved warmth of your rooms means you won’t want to change your system after all.

It is a relatively more tricky procedure, and must be done by an expert. Typically this will cost a few hundred pounds. You should be aware that some older radiators could show up a leak and you’d a new radiator, but flushing really is worthwhile as your heating system should be a lot more efficient as a result.

It is also a good time to get a cleaning system like magnaclean (a magnetic filter), which helps to keep the radiators crud free in future, although this will usually be done when installing a new boiler anyway.

Old vs. new radiators

We often get asked when a customer is considering a new boiler – should we also change our radiators? There are several things to consider with this and it is not a straightforward yes or no answer, but some key things you should remember are:

    • After flushing your old radiators when installing the new system, there is a small chance you will get leaks, so you should be aware that you may need to install replacement radiators at this point anyway.
    • If your old radiators are quite small, they will need to be hotter to heat the room to your preferred temperature, which means the boiler is working harder. Larger radiators are more efficient as they can run at a lower temperature and still heat the room sufficiently.
    • Some older radiators may not be able to handle the output from your new boiler, especially if you are getting a combi or a larger boiler than you had previously. Your installer should be able to help you with this.
    • New radiators are often not included in any quote you get, so be aware that you are going to be paying more if you go for new ones!

How much do new radiators cost?

Typically a new radiator will cost less than £100 (this will depend on the size) and you will have to pay for the installation as well. But remember, it is important to get the right size for the room – don’t just assume that the radiators you have already are the right size and replace them with similar.

What type of radiators should I install?

Firstly you need to decide which type of radiator you are going for.

The single and double panel radiators (which can be seen below) are the older style – and nowadays if you go into a DIY store you are not going to be able to buy this type of radiator.

Single Panel Radiator Infographic
Double Panel Radiator InfographicIt may well be worth replacing this type of radiator instead of going through the costly process of flushing it out and if you do decide to do this, you will probably get away with using a smaller convector radiator because the through out more heat.

There are three main types of convector radiator (which you can see below):

  1. Single Panel Convector radiators
  2. Double Panel Convertor radiators
  3. Double Panel Double Convector radiators

Single Panel convector Radiator InforgraphicDouble Panel convector Radiator InforgraphicDouble Panel Double convector Radiator InforgraphicThe panel refers to the long metal tanks that run parallel to the wall – it is these that fill with the hot water from your central heating systems and emit heat around the room. The longer the panel, the larger the heat emitting surface area, so bigger radiators will emit more heat, but also remember that a double panel radiator will emit more heat than a single panel radiator of the same length.

The convector fins (the zig-zagging metal strips) are welded to the panels and these are used to increase the surface area of the radiator so it emits more heat in a room. As mentioned previously, if you are replacing an older radiator without the convector fins, it is possible to install a much smaller convector radiator that will produce the same amount of heat.

The final thing to consider when buying a new radiator is the style at the top. Round top radiators allow you to see the convector fins, while compact radiators have a grill across the top of the panels that obscures the view of the convector panels. The performance of the two types of panel is pretty much identical, so this comes down to the finish you prefer!

Before you guy out and buy the radiator, you need to calculate the heating requirements of the room to ensure you buy the correct radiator size.

Sizing your radiator

The heat requirement of individual rooms is absolutely key to choosing the correct size radiator. For example, If you have a huge room with lots of external solid brick wall (notoriously bad at retaining heat) and you have a small single panel convector radiator fitted, it is likely the room is going to still be very cold, so you are going to need to supplement the heat.

There are software tools available that let you work out the exact heat demand of the room in question. These take into account the wall type, insulation present, the floor type, size of the room, amount of external wall and the intended use for the room.

Once you have your heat demand – typically several kilowatts or more – you can then use an equation like the one below to determine the length of the radiator required (this is based on a 50cm high radiator:

Length = Heat Demand (Watts) / (X*62)

Where X is a factor (0.09 for single panel radiators with no convector, 0.13 for single panel convector, 0.19 for double panel convector and 0.24 for double panel double convectors).

This equates to a difference of around 50% between the single convectors and double convectors, so it really does make a big difference.

With modern boilers, it is always best to design for a slightly larger radiator than you think is necessary – apart from the initial extra cost, there are not really any additional costs further along the line, since you can use thermostatic radiator valves to control the temperature of the individual radiator.

Where should my radiators go?

The British standard is to place radiators on external walls under windows where possible. The external wall is easier to mount and these are usually the coldest areas of the room, so it will help to offset that and create a more evenly warmed room. On the downside, curtains above the window may shield the radiator, and heat will be lost through the exterior walls and windows. Installing a radiator shelf above the radiator, and using reflective materials such as Radflek can really help reduce this heat loss. You might also wish to install a radiator fan to ensure the hot air gets evenly dispersed through the room (meaning the heat is felt more effectively so you can turn down the heating).

Radiator cabinets and furniture

Although they may hide the radiator from view, radiator cabinets can seriously reduce the heat output of the radiator. If you are planning to hide the radiator away like this, you will have to get bigger radiators. Likewise, if you have furniture directly in front of your radiators, it will absorb the heat produced, therefore installing a radiator fan will help redirect the heat around the room helping it to warm up quicker.

Which radiators are most efficient and are radiator boosters worth it?

All radiators effectively have the same efficiency – they give off the heat depending on how hot the water is being pumped into them. As we have mentioned however, the more panels and convector fins the radiator has, the more heat it will give off. All this means is that you can get away with a smaller radiator for the room than you would have with a single radiator however – they are all equally efficient (i.e. same cost per unit of heat).

The type of metal the radiator is made out of will determine how quickly it heats up – so an aluminium radiator will heat up a lot quicker than steel. This should not be an issue if you have a thermostat, as it will keep the room at a constant temperature.

Devices like radiator boosters and other fan assisted devices for radiators can help heat the room up more quickly so should be worth considering.