How do I size AHU heating and cooling coils?

Enter fresh air rate, outdoor and room design conditions, and room sensible/latent loads. The calculator splits pre-heat, re-heat, and cooling duties.

Should fresh air load be included in coil sizing?

Yes. Fresh air treatment (heating, cooling, dehumidification) is often the dominant coil duty — especially in winter pre-heat.

How does this relate to duct sizing?

Coil duties set the air handling requirement; duct sizing checks that the distribution system can deliver the design airflow at acceptable velocity and noise.

BuildFlo Design Guide · Ventilation · CIBSE Guide B

AHU coil capacity calculator

Calculate AHU heating and cooling coil duties from fresh air and room loads. Free air handling unit coil sizing calculator.

What this calculator does

AHU coil capacity helps UK building services engineers with heating/cooling coil duty from fresh air and room loads. The calculation follows CIBSE Guide B methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "ahu coil capacity", "ahu coil capacity calculator", or "how to ahu coil capacity", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: kW.

Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about ahu coil capacity under UK standards.

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Frequently asked questions

How do I size AHU heating and cooling coils?: Enter fresh air rate, outdoor and room design conditions, and room sensible/latent loads. The calculator splits pre-heat, re-heat, and cooling duties.
Should fresh air load be included in coil sizing?: Yes. Fresh air treatment (heating, cooling, dehumidification) is often the dominant coil duty — especially in winter pre-heat.
How does this relate to duct sizing?: Coil duties set the air handling requirement; duct sizing checks that the distribution system can deliver the design airflow at acceptable velocity and noise.