The 7 Most Common Radiator Questions

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Our resident radiator expert, Grant Doe, recently trawled Google to find out the most common questions that people were asking about radiators.

Taking the 7 most frequent questions, Grant used his knowledge and expertise to give you the answers to all your radiator queries in 1 handy blog.


What are the most efficient radiators?

Each radiator is as efficient as the next. What increases the efficiency of a radiator is ‘surface area’. A radiator with convector fins on the back will have a higher out put than one of the same physical size that does not


How do you bleed your radiators?

To bleed a radiator you will need to have a bleed key. Be aware of which side of the radiator the bleed valve is on.

While the heating system is off and cold, hold a rag under the bleed vent and open the bleed screw. Keep it open until just air comes out – it is important not to take the screw out fully.

The water that comes out of radiators will often stain fabric so it is important to protect carpets, curtains, bedding, clothing etc when bleeding radiators. If you have a combination boiler (no hot water cylinder in your airing cupboard) you need to check the pressure on the central heating pressure gauge after bleeding a radiator – it should read 1 -1.5 bar cold.



What is the different between single and double panel radiators?

Single panel radiators have only one side and one set of convectors. They are approximately 50mm thick depending on manufacturer.

Double panel radiators have two sides and two sets of convector fins. Again depending on manufacture, they are approximately 100mm thick.

Double panel radiators have a higher out put than single panel radiators as they have a larger heated surface area


Why are my radiators not getting hot?

The most common cause of a radiator not getting hot is air, see ‘how to bleed a radiator’


Why is my radiator cold at the bottom?

Sludge or ‘Magnatite’ is the most common cause for the bottom of a radiator to be cold. A system flush or flushing the radiator through with a hose will normally solve this issue


How many radiators do I need?

It is common place to have a radiator in all habitable rooms.

Placing them on the coldest wall of the room (usually external walls beneath windows) will aid heat convection to the centre of the house, hence the term ‘central heating’


How do thermostatic radiator valves work?

Thermostatic radiator valves work by sensing the air temperature of the room they are installed in. In the head of a thermostatic radiator valve there is a wax capsule that expands at a certain rate when temperature is sensed, as the room reaches the desired temperature, the wax capsule expands and it stops the flow of hot water to the radiator – if the room cools down the wax capsule contracts and the valve opens allowing water to flow to the radiator again.

An extremely common misconception is that a thermostatic radiator valve alters the temperature of the radiator to touch – it does not, but radiators from room to room may appear to be at different temperatures as they are opening and shutting


What size radiator do I need?

In order to get the best performance from your heating system a radiator must be sized to exceed the heat loss of the room. There are many algorithms to aid correct sizing of radiators but there are also some simple calculation tools online.

In order to use an online calculator you will need to be aware of the length, width and height of your room. You should also be asked what the room is used for (bathrooms, living rooms, bedrooms and habitable space all have different design temperatures depending on perceived activity levels in the room) how many outside walls the room has, the floor construction, wall insulation levels, the direction the room faces (south facing rooms require less heat due to solar gain than north facing rooms)


Answers compiled by Blue Flame’s Maintenance Team Supervisor, Grant Doe.

“It’s hard not to go ‘full geek’ where radiator sizing is concerned!”