Top Tip for TRVs

Top Tip for TRVs

Gareth Ash of Danfoss asks whether the method favoured by many installers of fitting TRVs in what is often referred to as Bottom Bottom Opposite Ends (BBOE) delivers optimum performance – or is it time to consider an alternative?


With space heating and hot water accounting for over 60% of a typical domestic energy bill in a year, the heating system – and how it is controlled – can have a big impact on fuel costs for end-users. Under the Energy Performance of Buildings Directive (EPBD), fitting individual room temperature controls, such as TRVs, is among a number of requirements for new buildings, and existing buildings when heat generators are replaced. When properly selected and installed, TRVs are proven to provide accurate temperature control in individual rooms, reducing heating costs and enhancing comfort for consumers. They also offer a relatively low cost solution, with a short payback period, and are quick and easy to fit in new or retrofit installations – all important factors for installers and their customers. So the benefits of TRVs are clear, but could the choice of installation method optimise these benefits?
On mainland Europe and in Scotland, for example, TRVs are generally installed Top Bottom Opposite Ends (TBOE) with the TRV feed at the top and the outlet on the opposite end at the bottom of the radiator. So what are the advantages of adopting this method as opposed to the BBOE approach? Firstly, there is the obvious issue of easier access to the TRV if a manual adjustment is required. Put simply, when the TRV is at the top of the radiator, rather than the bottom, users don’t have to bend down to reach it. In addition, it is much more difficult to try and read the numbers when the sensor is down at floor level in a dimly lit area. Whilst TBOE installation does, of course, offer these advantages to all users it can be of particular benefit to the elderly or to complement Part M accessibility design considerations for properties occupied by the disabled.

As well as the access issues, when a TRV is mounted at the bottom of the radiator it may be masked by furniture. To work efficiently, a TRV needs a free flow of air to sense the air temperature around it. Any obstruction to this free flow is likely to make the device think that the room temperature is higher than it actually is, resulting in a false temperature reading and inaccurate operation.
There is also an important efficiency factor in recommending that the inlet and the outlet are at opposite corners of the radiator. If both are at the bottom the hot water can simply pass through the radiator without necessarily heating the top. Installing the TRV to the top ensures better coverage of hot water through the radiator. A bigger surface area to heat also means that the return flow temperature is lower, so the boiler is more likely to be operating in condensing mode for increased energy savings. A further benefit of mounting the TRV at the top is that any dirt and rust particles from pipework and from inside the radiator are more likely to settle inside the radiator, rather than being transported around the system.

Some might say that the BBOE method has become the norm for most UK installers for aesthetic reasons because the TRV is out of sight at the bottom of the radiator. But is this consideration really worth the cost of compromising the TRV’s performance and the potential energy savings? Also, unlike their bulky manual predecessors, today’s smart electronic TRVs feature sleek, contemporary styling and often come in a choice of finish to blend in with interior décor.

Vertical vs Horizontal
Having considered some of the reasons for switching to TBOE installation of TRVs, let’s take a look at some of the advantages in fitting these devices horizontally rather than vertically. The vertical attitude tends to be the preferred option for most UK installers but this common practice means that the TRV sensor is placed immediately above the hot water pipe. This is likely to create a false temperature reading and affect the TRV’s ability to maintain the set room temperature: if the TRV is installed horizontally this is not an issue as there is less flow temperature dependency.

Simple change
Industry research and regulations endorse the fact that fitting better heating controls, like modern TRVs, put homeowners in charge of their energy consumption and help them keep their homes comfortably, and perhaps most importantly, affordably warm. By changing the way they fit TRVs could help installers increase these benefits for their customers. At Danfoss we fully appreciate that change can be a challenge for busy heating installers, whether it’s getting to grips with the latest regulations, embracing new technology or adapting to different working practices. However, for those not already using the TBOE method when fitting TRVs, we believe making this simple change is definitely worth considering. For more information visit