HVAC Engineer Interview Questions UK: 8 Real Questions and What Interviewers Want

Applying for a HVAC Engineer job in the UK? Here is what you are likely to be asked. These questions come from our HVAC Engineer question bank of 16 questions, written for UK employers at mid-level level.

Eight HVAC Engineer interview questions, and what the interviewer is thinking

1. Can you explain the main components of an air handling unit and how each affects the air delivered to a building?

Why they ask: Air handling units are central to most commercial HVAC work, so they test whether you know how they work.

2. What does a typical working day for an HVAC engineer involve, and what attracts you to this field?

Why they ask: They want a realistic picture of why you chose building services and whether you will stay.

3. What is TR19, and how would you decide whether a ventilation system needs cleaning?

Why they ask: Ductwork hygiene is a standard compliance topic for building services engineers.

4. How do you balance and commission an air distribution system, and which instruments do you use?

Why they ask: It shows whether you can prove that a system delivers the design airflows, rather than just running.

5. An office manager complains that one floor is stuffy and too hot while the floor below is comfortable. How would you investigate?

Why they ask: They want to see systematic troubleshooting of comfort issues, which is a daily HVAC call.

6. How does a chilled water system work, and what would you check if a chiller keeps tripping on low flow or high pressure?

Why they ask: Larger buildings rely on chillers, and fault-finding them is a common mid-level task.

7. What is a building management system, and how do you use it when maintaining HVAC plant?

Why they ask: BMS knowledge is key to fault-finding and energy management in modern buildings.

8. Tell me about a time you commissioned or handed over an HVAC system and had to deal with a problem that came up late.

Why they ask: They want to see how you cope when programme pressure meets technical issues.

A sample answer to question 1

Can you explain the main components of an air handling unit and how each affects the air delivered to a building?

A typical AHU takes in outside air and mixes it with return air through dampers, then passes it through filters, usually a coarse G4 panel followed by finer F7 or F9 bag filters. It then goes through heating and cooling coils, sometimes a humidifier, and finally a supply fan, usually driven by an inverter, which pushes conditioned air into the ductwork. Many units also have a heat recovery section, such as a plate heat exchanger or thermal wheel, to take heat from the extract air. Each part affects the result: blocked filters raise fan energy and reduce airflow, coils set supply temperature, and dampers control fresh air and mixing. During maintenance I check belts or direct drive motors, bearings, damper actuators, condensate trays, coil fins and filter pressure drops against the commissioning figures, because a rise in pressure drop tells me when filters really need replacing.

Common mistake to avoid: Missing out filters or heat recovery; describing parts without their effect

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the HVAC Engineer interview questions page. The first five are free, no sign-up needed.