Quick answer
Prepare commercial HVAC for winter in early autumn, before the first cold weather. Check that heating plant and heat pumps are serviced and running, AHU frost protection works, fresh air dampers close, controls have changed over to heating with correct schedules and setpoints, exposed pipework is protected, and condensate drains from outdoor units cannot freeze.
Why pre-winter checks matter
Winter failures tend to be worse than summer ones. A failed heating valve or frost thermostat can let a coil freeze overnight, causing water damage and a long repair. Heating complaints on the first cold Monday morning are often caused by controls that were never changed over from summer settings.
Most of these problems can be found in a planned pre-winter visit in September or early October.
Heating plant
Whether your heat comes from gas boilers, heat pumps or a district heating connection, check that:
- Heating plant has had its annual service and any defects have been closed out
- Plant has been run under load before the cold weather, not just test-fired
- Pumps, including standby pumps, run and change over correctly
- System pressure is correct and pressurisation units are working
- Strainers are clean and air has been vented from high points
- Safety devices and alarms are working and reaching the BMS or alarm contacts
Work on gas appliances must be done by Gas Safe registered engineers. Flair Facilities Ltd covers commercial boilers and plant rooms. This website deals with the HVAC side: heat pumps, air handling units, fan coils and controls.
Heat pumps
Air source heat pumps work harder and defrost more in cold, damp weather. Before winter:
- Clean outdoor coils and clear leaves and debris
- Check that defrost operation is working and condensate drains away freely
- Make sure drain lines and trays cannot freeze, using trace heating where fitted
- Check that outdoor units have clear airflow and are not recirculating their own cold discharge air
- Review flow temperatures and weather compensation settings
- Confirm any backup heating and its control sequence
Air handling units and frost protection
Frost damage to AHU heating coils is one of the most expensive winter failures. Check that:
- Frost thermostats or sensors work and trip at the intended temperature
- Heating valves open fully when the frost sequence calls for heat
- Fresh air dampers close tightly when units stop
- Frost sequences still operate outside occupied hours
- Heat recovery is working, as it reduces the load on heating coils
- Any coils that are drained or glycol-protected have been checked
See AHU maintenance and common faults.
Fan coil units and terminal units
- Heating valves and actuators respond to demand
- Two-pipe changeover systems have been switched to heating
- Filters are clean before the heating season
- Controllers are not locked in cooling mode
Controls and schedules
Controls problems cause a large share of winter comfort complaints. Check:
- Heating and cooling changeover logic and deadbands, so systems do not heat and cool the same space at once
- Optimum start settings, so buildings reach temperature for occupancy after cold weekends
- Time schedules, including bank holidays and the Christmas shutdown
- Frost protection setpoints for unoccupied periods
- Outside air temperature sensor readings against a reference
See HVAC controls and BMS and why some rooms are too hot or too cold.
Exposed pipework and outdoor equipment
- Insulation and trace heating on roof and external pipework are intact
- Chilled water and condenser circuits that run in winter have adequate glycol concentration where designed for it
- Drains, gutters and outdoor plant areas are clear so meltwater and rain can drain
Ventilation in winter
It is tempting to reduce fresh air in winter to save heating energy. HSE guidance says workplaces must still be adequately ventilated. If ventilation rates are reduced, it should be a deliberate controls decision, using CO2 or occupancy-based control where possible, not the result of dampers that have failed closed.
Over the holiday period
If the building will be empty over Christmas, agree in advance:
- reduced heating setpoints and the frost protection settings
- who receives alarms and how they will be handled
- how to reach the maintenance contractor or 24/7 contact line
A planned maintenance contract can include a pre-winter visit as standard. To arrange HVAC servicing before winter, call 020 7998 9005.
Frequently asked questions
When should pre-winter HVAC checks be done?
Ideally in September or early October, so heating plant, frost protection and controls are proven before the first cold nights. Problems found then can be fixed in planned time rather than during an outage.
What is frost protection?
Frost protection is a control sequence that runs pumps and heating, or closes dampers, when temperatures fall towards freezing, to stop water in coils and pipework freezing. It often operates when the building is unoccupied, so it needs testing rather than assuming.
Is it normal for heat pumps to steam or stop in cold weather?
Air source heat pumps run defrost cycles in cold, damp weather, and steam from the outdoor unit during defrost is normal. Frequent or long defrosts, ice building up on the coil, or units stopping on alarms are not, and should be checked.
What is the minimum temperature for an office?
HSE's approved code of practice for the Workplace Regulations says the temperature in workrooms should normally be at least 16°C, or 13°C where work involves rigorous physical effort.
Who services commercial gas boilers?
Work on gas appliances must be carried out by Gas Safe registered engineers. Flair Facilities Ltd covers commercial boilers and plant rooms on flairfacilities.co.uk.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- Workplace temperatures Health and Safety Executive
- Workplace (Health legislation.gov.uk
- Ventilation in the workplace Health and Safety Executive
This guide is general information for commercial building operators. It does not replace an assessment of your building by a competent engineer. If there is an immediate risk to people, contact the emergency services first.