How Not to Blow It During Your Job Interview

In Articles by Scott Wilson

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Well-Spoken, Squared Away, Firm Handshake… and You Better Know Your Stuff Too

Go into any HVAC shop today and you’re going to see a group of smart, technologically sophisticated guys who know the job … and part of knowing the job means knowing how to represent your employer by being squared away and well spoken.
All the rules of big boy conduct apply to presenting yourself as someone that’s going to fit in with a savvy group like this: Looking sharp, making eye contact, and offering a firm handshake still go a long way.

But that’s just the basics to make sure you don’t get laughed out the door before you get a chance to show what you’re worth. Ultimately, we are talking about HVAC here, so what really matters at the end of the day are a strong mechanical inclination, a mind for problem solving, and an enthusiasm for learning.

Of course, you’re going to show up early prepared to talk about your long-term career goals with the company, bring your own pen and notebook to write in, keep your cell phone turned off, and have answers in mind for the standard questions …

  • Describe a time you faced a challenge and how you overcame it?
  • What can you offer the company that others cannot?
  • What would you do if you’re asked to do something that you’re not qualified to do?
  • Give an example of a challenging situation that involved a customer, and how did you overcome this challenge?

And naturally, you’re going to put a positive spin on any challenging situation you describe to emphasize the successful outcome. And if you happen to have a three-month period of unemployment in your work history from a layoff last spring, tell them you’re looking forward to working with a company where you can get as many hours as possible, especially during the slow season.

You can find the basic tips for how to tap-dance your way through a job interview anywhere. What we’re talking about here are the things you’re going to need to know if you want to ace your job interview for an HVAC position.

Come with Credentials … and Tools

Coming with some credentials shows that you’ve got initiative, valuable skills and knowledge, and that you’re less of a liability.

Ideally you should come to your interview with a copy of your EPA Section 608 certification in hand. Unless you’re working in a specific niche of HVAC where you know you only need certification for sealed equipment containing 5 pounds or less of refrigerant (Type 1), high-pressure appliances (Type II) or low-pressure appliances (Type III) specifically, you should get the Section 608 Universal Certification that covers all types of equipment that uses controlled refrigerants.

You can even take a pre-exam course and test for the certification all in the same day for just a few hundred bucks. You’ll make that money back fast once you find a job a month sooner than you would’ve without it. Section 608 Certification is common so that also means a lot of the people competing for the same position are going to have it. All the more reason to get it sooner than later.

There are plenty of other HVAC certifications out there, sponsored by national organizations like NATE, the EPA, OSHA, and others. These typically involve completing a training course that can be done online or in-house at a local school, trade association, HVAC parts distributor, or union. The courses can last anywhere from a few hours to a few weeks or even months, and usually end with a cumulative test.

How do you know what certifications to get? Check with the local HVAC employers in your area and ask them what certifications they’re looking for from new hires. Even a quick look at local HVAC job ads will give you a picture of what shops in your area expect to see from job candidates. Once you’ve checked with several shops you’ll start to see some common certifications emerge.

Some of the more common certifications employers like to see in addition to the EPA Section 608 card are actually relatively quick and affordable:

If you have completed a comprehensive HVAC diploma or associate’s degree program through a trade school or community college, that is a big plus, and you should definitely do everything you can to highlight this. Detail each concept you learned on your résumé and bring a copy of your official certificate, diploma, or degree to your interview.

If you have your own tools it can be a plus to mention this. It shows you have initiative and hands-on experience. Your employer is always going to ask if you have your own transportation to get to work.

Cheat Sheet – Answers to Common HVAC Interview Questions

You’d better hit the books before your interview. This isn’t flipping burgers, washing dishes, or driving a truck. You’ve got to be prepared to answer complex questions that only someone with plenty of technical knowledge could answer. Many employers will even give you a short test at your job interview.

The following concepts are pretty universal in HVAC and are among the things you should have committed to memory …

What is cooling or heating load, and what factors do you consider when calculating this?

The cooling/heating load is the thermal energy that must be removed from (cooling), or added to (heating), a space in order to maintain a desired temperature.

Factors to consider when calculating this are:

  • Heat given off from lighting
  • Computers and electronic equipment
  • Solar radiation, and heat loss, through glass
  • Floor, walls, and the ceiling or roof
  • How many people are usually in the room
  • Infiltration/exfiltration of air
  • Dry bulb temperature and air humidity-temperature (wet bulb)
  • Ventilation
  • System heat gains
  • Climate zone
  • Which direction windows face
  • Insulating materials

What are the different units of measurement for thermal energy?

Thermal energy can be measured with several different units:

  • British Thermal Units (BTUs) – The amount of energy required to raise one pound of water by one degree Fahrenheit (°F)
  • Kilocalories (kcal) – The amount of energy required to raise one kilogram of water by one degree Celsius (°C)
  • Kilojoules (kJ) – The amount of energy needed to apply one newton of force to an object with a mass of 1,000 kilograms to move it a distance of one meter
  • To convert between any of these use: 1 BTU = 1.06 kJ = 0.25 kcal

What are the different ways heat can be lost or gained?

  • Conduction – energy transferred by direct contact
  • Convection – energy transferred by the mass motion of molecules
  • Radiation – energy transferred by electromagnetic radiation

What are negative pressure and positive pressure?

Imagine two walled cubic rooms of equal size next to each other, separated by a door with a half-inch gap underneath it. When the airflow into the room on the left is greater than that on the right, the room on the left has positive pressure, and air will flow under the gap in the door towards the room on the right. The room on the right has negative pressure with the opposite characteristics.

What is diffuser size, what are the variables in calculating it, and why is it important?

Regarding ventilation systems, diffuser size is the diameter of the neck of the air duct that spreads air into the room. Basically it’s the air vent where hot or cold air enter into the room.

Variables that must be considered when calculating the diffuser size are:

  • A room’s total area
  • Length and width of a room, as well as its ceiling height

If the diffuser is too small it will create noise because of restricted air flow. In general diffuser sizes are as small as possible because they don’t look nice. Diffusers that are too large will look out of place.

What is relative humidity, saturation point, and what is the relative humidity at saturation point?

  • Relative humidity – In simple terms, this is the percentage of humidity inside a building.
  • Saturation point (dew point) – This is when the air is holding its maximum amount of water vapor. This increases as temperature increases. When air is at its saturation point (dew point), any decrease in temperature will result in water condensation.
  • Relative humidity at saturation point – 100 percent

What is a heat pump, heating, and refrigeration?

Heating and refrigeration involve moving heat from one location to another. Both involve a heat pump (motor that transfers heat from a source) and a heat sink (destination of heat).

It’s easy to conceptualize heating an office building with this model: heat is generated and then the heat pump transfers it to the room to be heated.

A refrigeration cycle also uses this process. Within a closed loop, refrigerant (anything that changes between a liquid and gas) in gas form is compressed with a heat pump to the point where it becomes a liquid.

The condensed liquid refrigerant is then sent through a long coil that ends up at an expansion valve into a larger chamber. Once in the chamber on the other side of the expansion valve the pressure decreases, resulting in cooling, with the refrigerant also becoming a gas.

Just imagine when you blow on a hot drink to cool it off. The air coming out of your mouth is cold because it’s moving from higher pressure to lower pressure.

Air is blown over this expansion chamber, which cools the air, and then that cold air is vented to the place that needs to be refrigerated.

Meanwhile back in the closed loop the refrigerant is sent back to the compressor where we started, and the cycle starts over.

In this refrigeration cycle, the heat pump is the compressor. When the refrigerant is compressed it heats up. While it travels along it’s long route to the expansion valve, the compressed refrigerant radiates this heat away to the external environment. So the external environment is actually the heat sink.

What Your Résumé Should Look Like

Your résumé should detail your qualifications, education, employment history, skills, and a positive closing statement, in that order. If you have any volunteer or other related experience that shows you’re enthusiastic, helpful to customers, or a positive team player then include that just before your closing sentences.

List your employers in chronological order, starting with the most recent. For each employer you’ve had, include a list of activities you performed and the skills you used. List your official job title. If you were promoted list each successive job title. Clearly list the dates you started and ended each job.

Research the company you’re applying to. Find out what kind of HVAC they do and highlight, or even rewrite, the details of your résumé that emphasize what each individual employer is looking for.

At the end of your résumé include a closing sentence or two that explains how you are eager to make a long-term career in HVAC.

Here’s an example of a straightforward résumé format – model yours after this …



  • EPA Section 608 Certification – Universal
  • OSHA 10-hour Construction Safety Certification
  • R-410A Refrigeration Certification


Diploma in HVAC/R from Mountain Technical College, 3-month program, 2012.

  • Principles of refrigeration, including recycling and recharging refrigerants
  • Electrical fundamentals, components, and motors
  • Preventative maintenance and diagnostics on heat pumps, residential and gas
  • Tubing fabrication and fitting, including brazing and soldering
  • Building heating code and licensing
  • Building engineering and hydronics

Professional Experience

Best Heating and Cooling Company, October 2012 – Present

Job title (starting): HVAC Technician – job title (final): Lead HVAC Installation Manager

Contact: Jane Doe (555) 555-5555 | 101 W. 1st Ave; Paradise, MT |


  • Lead and manage HVAC installations – supervise and direct employees, consult with clients, maintain smooth operations for projects completed ahead of schedule and under budget
  • Install 2-ton HVAC units – test units for leaks, properly connect all power, braze/solder all pipes and lines, supervise employees for proper installation procedures and safety, troubleshoot problems
  • Et cetera

Unpaid Experience and Accolades

  • In 2008 my friends and I built a go-cart that won the 25-mile “Off-Road Warrior” race; I was responsible for designing and building the exhaust system
  • In 2007 I volunteered regularly at my church to help elderly members troubleshoot and fix problems with their computers

Thank you for your consideration

My long term goals are to excel in the field of HVAC while relying on my professionalism and continuous learning to maximize my longevity.

John Doe