Is your money going out with the air?  

The principle is simple. A balanced ventilation system extracts stale air and supplies fresh air. In winter, fresh air can enter at 0 °C and must be heated to around 20 °C before it reaches the offices. At the same time, the extracted air leaves the building at around 22 °C. Without a heat exchanger between the two flows, all that heat goes out through the roof, throughout the heating season. A modern exchanger recovers 75 to 85% of it. For a typical 10,000 m² office building with a 50,000 m³/h air handling unit, this could translate into annual savings of approximately €14,000 (200 MWh of gas), based on a gas price of €70/MWh. That is the heating consumption of some forty houses. Electricity adds to the bill: older fans often run on belt drives, at full flow all day, whatever the actual occupancy. 

In the four buildings where the upgrade was costed in detail, replacing the air handling unit cuts gas consumption by 10 to 32% and carbon emissions by 5 to 23%. 

For investors, the cost-effectiveness of this intervention is particularly compelling. At approximately €824 per tonne of CO₂ avoided, air handling upgrades are six to seven times more cost-effective than roof insulation or window replacement in the buildings studied. Beyond carbon savings, the impact on energy performance can also be significant. In one building, upgrading the air handling system alone was sufficient to improve its EPC rating from D+ to C. 

On the CRREM pathway, the picture is more sobering. Without works, 10 of the 13 buildings fall off the 1.5 °C pathway before 2033. Upgrading air handling alone buys one to two years. No single measure is enough, because the pathway tightens every year. But this one buys time at a lower cost than most.

On full project cost, the business case looks modest: €17 to €47 per m² of investment, €10,500 to €29,800 of annual savings, and a payback of 9 to 19 years in buildings without heat recovery. The decisive factor is the starting point. Where the existing system already recovers some heat, the payback stretches to 33 years: the potential has largely been captured. 

The real question, however, is when the unit will need replacing anyway. Many of these units will reach the end of their life within five to ten years, for maintenance reasons alone. In that case, the energy investment is only the extra cost of a high-performance unit over a like-for-like replacement, about half of the project. The payback then falls to 5 to 10 years, for equipment that will run for twenty. Lighter options exist, but they need care. Optimising ventilation controls without replacing the entire unit pays back in about 11 years and produced no EPC gain in the six cases studied. On a unit with only a few years left, it buys time rather than value. 

Upgrading air handling is not always the first priority. But leaving it out of a decarbonisation strategy can mean missing one of the most cost-effective sources of value in an office building. Three criteria identify the best candidates: no heat recovery on the existing ventilation, high gas consumption, and high airflow relative to floor area. The benefits likely go beyond energy: better control of fresh air, fewer cold draughts, less noise. Our studies did not measure them. The EPC gain, however, is documented, and it increasingly shapes access to green finance and tenant demand. Decarbonising an office building is  not about doing more works. It is about choosing the ones with the best energy, carbon and financial impact. That is why Pulse reviews energy line of a building, air handling included, before recommending works. Is the air in your buildings part of that analysis?