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

Applying for a HVAC Design Engineer job in the UK? Here is what you are likely to be asked. These questions come from our HVAC Design Engineer question bank of 12 questions, written for UK employers at mid-level level.

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

1. How would you size and select a heat pump system for a commercial building, and what factors affect efficiency?

Why they ask: Heat pump design is now the core of HVAC work in the UK.

2. What does the day-to-day work of an HVAC design engineer involve, and what do you enjoy about it?

Why they ask: It tests understanding of the role and sincere interest.

3. Explain how you would size a ductwork system, including how you would balance velocity, pressure drop and noise.

Why they ask: Duct design is a staple technical task.

4. What are the differences between VAV, fan coil and chilled beam systems, and when would you choose each?

Why they ask: System selection shows breadth and judgement.

5. During commissioning a ventilation system fails to achieve its design airflow in a key zone. How do you investigate?

Why they ask: Troubleshooting under pressure is part of the job.

6. Tell me about a time you designed or improved a system to cut energy use.

Why they ask: Energy performance is a major priority in current HVAC work.

7. How do F-Gas Regulations and refrigerant choice influence your design decisions?

Why they ask: Refrigerant regulations affect plant selection and long-term cost.

8. A client complains that an office you designed is too noisy because of the air conditioning. What do you do?

Why they ask: It tests diagnostic and client-handling skills after handover.

A sample answer to question 1

How would you size and select a heat pump system for a commercial building, and what factors affect efficiency?

I begin with an accurate heat loss calculation to BS EN 12831, including ventilation losses, then establish the design flow temperature, since this drives the seasonal coefficient of performance. I aim for low temperature emitters, such as oversized radiators, fan coils or underfloor heating, so that flow temperatures are around 45 to 55 degrees. I choose between air source, ground source or water source depending on site constraints, noise, space and capital budget, and I check the outdoor design temperature, usually around minus 3 degrees in most of England. The unit is sized for the design load with defrost and cold weather capacity in mind, often modular so that part load efficiency stays high. I add buffer volume, hydraulic separation and weather compensation controls. Efficiency is affected by flow temperature, source temperature, cycling, pipework losses and controls. I also check the refrigerant GWP, plant room space, electrical supply and Part L compliance before finalising.

Common mistake to avoid: Sizing from floor area rules only; Ignoring defrost and low temperature capacity

Want the rest?

Full model answers, key points and common mistakes for all 12 questions are on the HVAC Design Engineer interview questions page. The first five are free, no sign-up needed.