Coils are the workhorses of any air handling unit. Heating coils, cooling coils, and heat recovery coils all transfer energy between air and water (or refrigerant), and they do it continuously, often for decades. But they don’t last forever — and when performance drops, the impact on energy consumption, comfort, and system reliability can be significant.
We manufacture replacement coils and carry out coil replacements across commercial and industrial AHU installations throughout the UK. Here’s how to recognise when replacement is needed and what the process involves.
Signs Your Coils Need Replacing
Coil degradation is usually gradual, which means it often goes unnoticed until performance has declined significantly. These are the indicators we look for during our maintenance inspections.
Declining heat transfer performance. If your AHU is struggling to maintain supply air temperatures despite adequate water flow and temperature, the coils may be fouled internally or externally beyond what cleaning can resolve. Limescale buildup inside water coils and fin deterioration on the air side both reduce heat transfer over time.
Visible corrosion. Coil headers, tubes, and fins corrode — particularly in coastal environments, swimming pool applications, or anywhere with chemical exposure. Surface corrosion reduces fin efficiency. Header corrosion leads to leaks.
Persistent leaks. Individual tube leaks can sometimes be repaired by plugging the affected tube, but this reduces coil capacity. Multiple leaks or header joint failures usually mean the coil has reached end of life. We’ve attended sites where maintenance teams have been plugging tubes for years — losing 10-15% of coil capacity incrementally without realising the cumulative impact.
Excessive pressure drop. Fouled or damaged fins restrict airflow through the coil, increasing the pressure drop across the AHU. This forces fans to work harder, consuming more energy and potentially reducing airflow to the building.
Age. Coils in well-maintained systems typically last 15-25 years. Beyond that, degradation accelerates even with good maintenance. If your coils are approaching or past this age, proactive replacement during a planned shutdown is far less disruptive than emergency replacement after failure.
Replacement Options
Like-for-like replacement is the simplest option. We manufacture replacement coils to match the exact dimensions, connections, and performance of the originals. This minimises modifications to the AHU and ductwork, keeping installation time and cost down.
Upgraded replacement takes the opportunity to improve performance. Modern coil designs can deliver better heat transfer in the same physical footprint — meaning improved capacity or reduced pressure drop compared to the original. If your building’s requirements have changed since the original installation, an upgraded coil specification can address this without modifying the rest of the AHU.
When we assessed the four AHUs at Dalston Cross, coil performance was one of the key areas of deterioration. In cases like this, coil replacement as part of a broader refurbishment often delivers the best value — addressing multiple issues in a single planned intervention.
Material upgrades may be appropriate for challenging environments. Standard copper tube and aluminium fin coils suit most commercial applications. For corrosive environments, we can specify copper fins, coated coils, or stainless steel construction to extend service life.
The Replacement Process
Survey and measurement. We survey the existing installation to confirm coil dimensions, connection sizes and positions, and mounting arrangements. Getting this right ensures the replacement coil fits precisely.
Manufacture. Replacement coils are manufactured to order at our UK facility. Lead times depend on specification complexity but are typically 2-4 weeks.
Installation. Coil replacement requires the AHU to be shut down. We plan installations to minimise downtime — often during weekends, bank holidays, or low-occupancy periods. The old coil is removed, connections are prepared, the new coil is installed and connected, and the system is pressure-tested before restart.
For critical systems where extended downtime isn’t acceptable, we can pre-manufacture the replacement coil so it’s ready to install the moment the AHU is taken offline, reducing the shutdown window to hours rather than days.
Commissioning. After installation, we verify water flow rates, check for leaks, and confirm the new coil is delivering the specified performance. Temperature differentials and pressure drops are recorded as a baseline for future maintenance monitoring.
Energy Savings From Coil Replacement
Replacing degraded coils doesn’t just restore original performance — it can deliver genuine energy savings. A fouled coil with 20% reduced heat transfer means the heating system works 20% harder to compensate. That’s 20% more energy consumed, every hour, for the remaining life of the coil.
Modern coil designs with enhanced fin patterns and optimised tube circuiting can outperform original specifications, delivering even greater efficiency improvements.
We always calculate the energy implications of coil replacement as part of our assessment. In many cases, the energy savings alone justify the investment within 2-3 years.
Talk to Us
Whether you need emergency coil replacement, planned upgrades, or advice on coil condition as part of a wider AHU assessment, contact us to discuss your requirements.
