The hidden threat to HVAC systems

When we think about pollution, we often picture congested roads, industrial chimneys, or smog-laden city skylines.

Rarely does the conversation turn to HVAC systems—let alone the quiet corrosion of aluminium fins in heat exchangers.

And yet, pollution is one of the most overlooked threats to HVAC coil longevity, performance, and ultimately, a building's environmental footprint.

In this blog, I’m going to explore how airborne pollutants—particularly Nitrogen Oxides (and Sulphur Dioxides (SO₂)—are attacking HVAC systems across the UK.

I’ll also examine how this degradation ties directly into energy inefficiency, rising operational costs, and the broader national and corporate drive toward Net Zero.

Finally, I’d like to introduce a powerful yet underutilised data tool that can help specifiers, HVAC manufacturers, distributors and facility managers take proactive action: the UK National Atmospheric Emissions Inventory (NAEI).

The anatomy of HVAC coil corrosion

At the heart of every HVAC system lies the heat exchanger. These coils, usually made from aluminium fins over copper tubing, are designed for efficient heat transfer. But while these metals are excellent conductors, they are also highly vulnerable to corrosion.

Corrosion doesn’t announce itself dramatically. It starts microscopically and builds silently over time. A gradual accumulation of pollutants on untreated metal surfaces leads to:

• Reduced airflow
• Increased energy use
• More frequent maintenance
• Shortened equipment life
• Unexpected system failures

These symptoms often appear without warning, leaving maintenance teams reacting rather than preventing.

The chemistry of corrosion

So, what do NO₂ and SO₂ do to HVAC?

The UK's industrial activity, heavy traffic, and dense population mean that airborne pollutants are an ever-present risk—especially Nitrogen Oxides (NO₂) and Sulphur Dioxides (SO₂). These gases are produced largely by internal combustion engines, industrial processes, and fossil-fuel-based energy generation.

When NO₂ and SO₂ are released into the atmosphere, they don’t simply disperse harmlessly. They interact with water vapour and oxygen to form nitric (NHO₃) and sulphuric (H₃SO₄) acids. These acids fall back to the surface as acid rain or dry deposition, settling on all exposed surfaces—including HVAC coils.

The aluminium in untreated coils reacts with these acidic compounds, leading to pitting, etching, and eventual breakdown of the material. Over time, this degradation compromises both performance and structural integrity.

It’s not just a coastal problem

For years, the HVAC industry has rightly flagged coastal locations as high-risk environments due to salt-driven galvanic corrosion. However, this focus has unintentionally created a blind spot: the inland pollution threat.

Urban centres, industrial estates, logistics hubs, rail corridors, and even airport-adjacent buildings all experience elevated levels of air pollution—often without clear visual cues.

This is where many decision-makers fall short. They assume corrosion is only an issue near the sea. But the truth is, buildings miles from any coastline can still suffer from significant coil degradation due to airborne chemical pollutants.

Turning insight into action

One of the most underutilised resources in the UK when it comes to pollution and maintenance planning is the National Atmospheric Emissions Inventory (NAEI).

Freely accessible, this interactive tool provides detailed, postcode-level data on emissions across the UK—including concentrations of NO₂ and SO₂.

What makes this tool so valuable?

• Evidence-based planning: Facilities teams can make informed decisions about HVAC protection based on actual pollution exposure, not guesswork.
• Risk assessment: By overlaying HVAC asset locations with high-emission zones, engineers can identify vulnerable units before problems arise.
• Strategic investment: Businesses can target their maintenance budgets toward the most at-risk sites, maximising ROI and equipment longevity.

Despite its utility, the NAEI is rarely referenced in HVAC maintenance strategies or capital planning. It’s time to change that.

The net zero connection

As UK organisations align with the government’s legally binding net zero targets for 2050 (and often sooner for large corporates), the performance of HVAC systems is under increasing scrutiny.

In many commercial buildings, HVAC accounts for 40–50% of energy use. Any loss in system efficiency has a direct impact on a building’s carbon footprint.

Unchecked coil corrosion means:

• Higher compressor loads
• Longer run times
• Poorer indoor air quality
• Greater emissions

By protecting HVAC coils from corrosion, businesses not only avoid costly repairs but also directly reduce their Scope 1 (direct greenhouse gas) and Scope 2 (indirect greenhouse gas) emissions. This aligns with key Environmental, Social & Governance (ESG) goals and demonstrates a commitment to sustainable operations.

The business case for coil protection

Protective coatings, such as those provided by Blygold, form a microscopic, corrosion-resistant barrier over HVAC coils. These advanced formulations maintain thermal conductivity while sealing vulnerable metals against attack from acidic pollutants.

Applied either on-site or at factory level, the benefits include:

• Doubling the lifespan of HVAC coils
• Improvement in energy efficiency
• Lower maintenance requirements
• Fewer system failures and unplanned outages
• Alignment with Net Zero targets and ESG metrics

For most commercial HVAC systems, return on investment is achieved within 1–2 years. That’s before factoring in deferred capital expenditure and avoided disruptions.

Real-world applications

Using data to make smart decisions

Let’s take two hypothetical examples:

1. A logistics centre near a major motorway junction: NAEI data shows consistently high NO₂ levels.
   Without protective coatings, rooftop HVAC systems are exposed to year-round corrosion risk.
   By using NAEI data to justify coil treatment, the FM provider avoids unnecessary replacement costs and reduces energy bills.
2. A regional hospital near an industrial park: While not coastal, the area has elevated SO₂ levels from nearby activity. A review of emissions data prompts the estates team to treat coils in key areas such as theatres, wards, and imaging suites—safeguarding uptime and patient comfort.

These are not hypothetical benefits. They’re actionable insights made possible by combining pollutant data with proven protective technologies.

Next steps for HVAC stakeholders

If you manage HVAC assets in any of the following environments, it’s time to consider pollution as a primary risk factor—not a secondary concern:

• High-traffic areas (road or rail)
• Industrial zones or ports
• Airports or sites near flight paths
• Large car parks

Use the NAEI tool to assess pollutant levels by postcode. If levels of NO₂ or SO₂ are consistently elevated, your HVAC coils are at risk.

From there, explore options for Blygold protective coatings as part of your planned maintenance strategy or CapEx programme. Not only will you protect assets, but you’ll also be contributing to your organisation’s broader sustainability targets.

From overlooked risk to strategic advantage

Pollution-related coil corrosion is one of the UK HVAC industry’s most under-recognised challenges. But with the right data, protective strategies, and cross-functional collaboration, it’s also one of the most solvable.

By leveraging tools like the NAEI, specifiers, HVAC manufacturers, distributors and FM professionals can move from reactive maintenance to proactive asset management—extending the life of expensive HVAC systems, reducing energy consumption, and supporting their company’s Net Zero commitments.

At Blygold, we believe that data-driven maintenance is the future. And that starts with acknowledging that corrosion isn’t just a coastal issue—it’s a pollution problem.

With thanks to: © Crown 2025 copyright Defra & DESNZ via naei.energysecurity.gov.uk licenced under the Open Government Licence (OGL).

Simon Hammond is Business Development Manager for Blygold (UK) Ltd