Gareth Ash from 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?
Every year, millions of thermostatic radiator valves (TRVs) are installed worldwide. They remain one of the most effective and widely used forms of heating system control; yet, a fundamental question remains: Are we installing them correctly to achieve maximum comfort and energy efficiency?
With the shift from gas boilers to low-temperature heat pumps accelerating, the performance of every radiator in a home is under greater scrutiny. Heat pumps operate best when water flow temperatures are kept low, making even heat distribution across the system essential. Traditionally, most UK installers opt for the Bottom, Bottom, Opposite Ends (BBOE) method with vertical TRV installation. But as Gareth Ash, Marketing Manager at Danfoss, argues, it may be time to rethink convention and adopt the Top, Bottom, Opposite Ends (TBOE) horizontal method instead.
Why TBOE Works Better
On the continent, and even in Scotland, TBOE installation is the norm. By placing the TRV feed at the top of the radiator and the outlet at the bottom on the opposite end, installers can unlock significant performance benefits.
The key advantage lies in heat distribution. With BBOE installation, hot water can short-circuit across the bottom of the radiator, leaving the top underheated. TBOE ensures the entire radiator heats evenly, maximising surface area and lowering the return flow temperature – an essential factor for heat pump efficiency.
With the transition from gas boilers to heat pumps gathering pace, even heat distribution across radiators is becoming more critical. Heat pumps operate at lower flow temperatures, so extracting maximum performance from every radiator matters more than ever. Paired with pressure-independent TRVs and modern sensors, TBOE installation promotes uniform heat spread, helping systems work more effectively without overhauling the entire setup.
It’s also important to remember that for a TRV to work efficiently, it needs a clear flow of air to accurately sense the room temperature. When mounted at the bottom of a radiator, the valve can often be obscured by furniture, limiting airflow. This can cause the TRV to register a higher temperature than the room actually is, leading to false readings and inaccurate less operation.
There’s also a system health benefit: when the TRV is positioned at the top, dirt and rust particles are more likely to remain settled in the radiator instead of circulating through the system, improving longevity and reliability.
Vertical vs Horizontal
Generally, in the UK, we install TRVs vertically; however, this means that the TRV sensor is placed immediately above the hot water pipe. This is could lead to 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.
From a user perspective, accessibility is another clear win. With the TRV at the top of the radiator, adjustments are easier to make, numbers are easier to read, and users don’t need to crouch down to floor level. This is particularly beneficial for older homeowners or those living with reduced mobility, aligning neatly with Part M accessibility standards.
Overcoming the Aesthetic Objection
One reason BBOE has remained the norm in the UK is aesthetics: a TRV tucked away at the bottom of a radiator is less visible. But this consideration is increasingly outweighed by performance and energy savings. Today’s smart electronic TRVs are slim, stylish, and available in a range of finishes designed to complement modern interiors – proving that form doesn’t have to compromise function.
A Simple Change, A Big Impact
With household energy bills set to rise again this winter, homeowners are more conscious than ever of efficiency. A simple change to TBOE/horizontal TRV installation could be the change that ensures their homes are comfortably, and perhaps most importantly, affordably warm.
For installers, it’s a chance to stand out by offering customers a smarter, future-ready solution. For homeowners, it’s an opportunity to gain greater control over their energy consumption while keeping homes warm, comfortable, and affordable.
For more information, visit www.heating.danfoss.com
*Article originally published Jun 2021 and updated Oct 2025
