Radiators – What you can check for during a survey.

Original Article
November 10th, 2020


Radiators are the most common heat emitter in residential dwellings and they play an important role in heating our homes yet generally, radiators are not reported on in surveys. Older, unmaintained radiators can be inefficient, and this article explains the reasons why and simple checks you can make during a survey to provide clients with useful information with regards to the often-overlooked radiator.

How radiators work
Radiators in domestic dwellings are designed to heat the surrounding space through both radiation and convection. A radiator is generally heated through a primary heat source such as a central heating boiler or heat pump. The primary heat source creates heat (ordinarily by burning a fuel such as natural gas, oil, or LPG) which is then pumped around a heating circuit through each radiator.

A conventional radiator will have an inlet and outlet to enable hot water to run through the radiator and a closable air vent towards the top which allows the periodic release of any air that may have entered the system.

Figure 1 – the direction of water flow through a radiator

Modern v old
Radiator technology has quietly gone about a complete revolution in recent years. Huge efficiency gains have been made in modern radiators due to improved manufacturing technology, enabling lower content waterways and improved convection fins to maximise emitted heat.

Whilst many individuals regularly upgrade the boiler in their home, it is far less common to install new radiators; this is probably down to cost, property disruption and even a lack of understanding of the benefits. However, the impact of new radiators should not be underestimated: a heating system could achieve up to a 50% improvement in efficiency, just by installing new radiators.

Older radiators will have much less convection technology and they will require a higher water content in order to achieve the same output as a modern radiator meaning that a boiler is likely to have to work much harder and burn more fuel.

Years of use can also result in a build-up of sludge and scale deposits which cause inefficiency.

•    Sludge can affect the functionality of the radiator as it can prevent water flowing freely and instead water will enter the inlet and almost immediately exit, not heating the radiator properly.
•    Scale deposits absorb heat and thus diminish the level of heat being emitted into the room.

Figure 2 – old radiator

Modern radiators which hold low water content will be much more efficient, with the rear panel having much better heat retention and the front panel having higher heat emittance through a thinner and better-engineered fascia.

Figure 3 – modern radiator

What you can check
One of the challenges to inspecting a radiator is that it is difficult to determine much at all unless the heating system is fired-up, which may not be achievable as part of a survey. However, here are some simple checks you can carry out as part of a non-invasive survey:
1.    Check for leaks
Run a dry kitchen towel around the valves on both sides of the radiator to check for any signs of existing leakage. If there is a scaly deposit (like the image below) it is a sign there has been previous leakage.

Figure 4 – example of scaly deposit on the radiator valve

2.    Check for signs of sludge
Feel around the radiator (whilst heated), and if you find that there are colder spots around the bottom half of the radiator, it is likely due to the presence of scale and/or sludge. Bear in mind that one blocked radiator can have a knock-on effect on the other radiators in the system. You can try to establish which radiator could be blocked by working your way from the boiler to the first radiator in the system and if this radiator is heating up fine, move on to the next one. If the first radiator is cold, it is likely that this radiator is preventing the others from heating up correctly so this should be fixed first.

Figure 5 – thermal image showing sludge blocking a radiator

3.    Check for trapped air
Feel around the radiator (whilst heated), and if you find cold spots across the top of the radiator it may be signs of trapped air which can be released by using an air vent key.
Trapped air in a radiator can be caused by several reasons, such as:
•    A central heating pump installed above the supply tank
•    An open tank in the loft used for immersion heaters
•    A build-up of hydrogen in the heating system. This can be caused by rust or a build-up of sludge
•    Small pinhole leaks in the system which often means regularly topping up boiler pressure.

Figure 6 – bleeding a radiator

Other things to consider
Size of radiators
When installing radiators, a calculation should be made as to what size is required to give the optimum heat output. If the radiators are too small, then the desired temperature will not be reached, and if the radiators are too big, then the system will “overshoot” the desired temperature which would not be economical. Many online calculators can help to establish the “BTU” (British thermal unit) requirement for a room.
Number of radiators in a room
Usually, one radiator is sufficient (if it is the appropriate size); however, for rooms 6 metres or longer, it may be worth considering distributing several radiators to minimise the thermal gradient (the ratio of the temperature difference and the distance between two points) within the room.
Are there thermostatic radiator valves which enable better control over a radiator’s heat output? TRVs are used to adjust the flow of water into the radiator, depending on the setting, and thus control the heat output of an individual radiator. It may be that TRVs have been used to overcome the incorrect sizing of radiators to manage overheating.
Traditionally, radiators were placed underneath windows because it was colder there; however, this was not the most efficient place for them since a lot of heat would escape through the single-glazed window. These days, modern double glazing is much more efficient, and less heat will escape through the window.

Also, bear in mind that if a radiator is within 1 metre of a room thermostat, it may confuse the system into thinking the temperature is adequate although the rest of the room may not have reached an adequate temperature.  
To conclude
These are just some simple checks and considerations that can be used by surveyors and other property professionals when providing information to a homeowner.

Hopefully, you find these pointers useful and if you are in a position where you can conduct these checks during a survey and give the client feedback, we see it as excellent services and good value for money for a customer.