Green Link

Sharing our expertise to help you succeed

Darren Witter

Are you still experiencing HVAC comfort or efficiency problems in your facility?  It’s time for the next level of technical HVAC skill. Maybe you have realized you’re dealing with negative building pressure. You might wait on calling the air balance contractor and first become more informed about the problem with your management team.  It’s time to call in your trusted mechanical contractor (MC).

Your contractor’s first steps will be to inspect many of the same areas we advised in this post.   In addition, you should locate any past air balance reports and confirm that all the punch list items were corrected.  With these observations and baseline data as your starting point, you or your MC can begin to formulate a hypothesis. To dig deeper into problems, check the following areas where we most frequently find the causes of HVAC comfort issues:


1.   Filters Inside the Unit

Dirty, old, or clogged filters will restrict airflow through the unit.  Filters should be at least replaced quarterly for a commercial unit and can be added as part of a preventative maintenance scope of work. In the Restaurant Facility Management Association’s Facilitator Magazine's article "Staying On Top of Comfort Concerns," Red Lobster Facility Manager Angela Hughes writes, “The washable metal filters inside each makeup air fan need to be cleaned during major preventative maintenance.  These are often overlooked by HVAC preventative maintenance vendors.  Dirty filters can block airflow into the unit and greatly affect the building balance.  If the filters are damaged or missing, be sure to replace them.”

Dirty air filters

Dirty Outdoor Filters


2.  Coils Inside the Unit

Dirty, clogged, or frozen coils can also heavily restrict airflow through the unit. Mechanical contractors are equipped to unfreeze and clean coils.  Hughes explains, “Dirty coils will cause the unit to freeze up and temporarily shut down, which causes stress on the compressors.”  Further, if the rooftop unit (RTU) blower compartment and/or coils are dirty, then they are likely causing reduced airflow and contaminated air.  The solution is to clean internal components of the RTU.


Frozen evaporator coil

Frozen Evaporator Coil


Dirty RTU blower compartment

Dirty Rooftop Unit Blower Compartment


RTU dirty coil

Dirty Blower Wheel Inside Rooftop Unit


3.   Refrigerant Levels

Low refrigerant levels can lead to uncomfortably warm temperatures. Your mechanical contractor should be equipped to refill refrigerant.


4.  Outside Air Dampers

Open up the units to inspect the outside air dampers. The amount of outside air is specified in the building’s design; however, it is often adjusted later as a quick-fix for short term issues, leading to bigger problems in the long run.  It is common to find improperly installed and inoperable outdoor air dampers, which negatively impact the building pressure.  The dampers will need to be adjusted to proper position and outside air intakes may also need to be installed to achieve desired airflow.

Improperly installed air dampers

Improperly Installed Outside Air Dampers (Sealed Closed with Caulk)


5.   Negative Building Pressure

The tell-tale sign of negative building pressure can be found with using the "door test."  A quick way of checking your building’s air pressure is to test it with a lighter or a match at an exterior door.  Crack the door open and place a lighter in the crack as pictured below.  If the flame pulls toward the inside of building, then the building is negative.

Door lighter test


6.  Equipment Change 

Has your facility undergone a remodel, renovation, or a major change in equipment? Remodels, renovations, or major equipment replacements change the distribution of airflow and require an air balance service.  HVAC equipment installed in a building will not function at design specification at start up.  Adjusting the system to design specification requires testing, adjusting, and balancing.



These are just six  examples of what your mechanical contractor may discover in their assessment process.  If they are able to find and properly resolve the HVAC comfort or efficiency issues, then your troubleshooting may end here.  If not, you may need to consider calling in a certified test and balancing firm.  Get tips on what to look for when hiring a test & balance contractor.


  • Angela Hughes, a Red Lobster Facilities Manager with distinguished technical knowledge of HVAC systems, authored a very practical approach for FMs to self-diagnose comfort problems without prematurely spending money on contractors. Staying On Top Of Comfort Concerns.
  • For suggestions on preparing for an air balance, read Optimizing Air Balance Report Data by Greg DuChane, Retail-Restaurant Vertical Market Director at Trane.
  • DuChane, Greg. “Optimizing Air Balance Report Data.” Trane Tracks (Apr. 2015): n. pag. Trane. Web.
  • Hughes, Angela. “Staying On Top Of Comfort Concerns.” Facilitator Magazine Apr/May (2015): 66. Restaurant Facilities Management Association, 25 June 2015. Web. 26 Aug. 2015.
  • Melink Test & Balance Technicians. HVAC Deficiency Images. Digital image. Melink Test & Balance. Melink Corporation, n.d. Web. 26 Aug. 2015. 



Darren Witter

About Darren Witter

Darren Witter, Sr. Vice President, has been with Melink Corporation since 1996. He has served in a variety of capacities including engineering, product development, manufacturing, field services, and management. Darren earned a mechanical engineering degree from the University of Cincinnati and is a State of Ohio Professional Engineer (PE). He is also qualified as a LEED Accredited Professional and a NEBB Certified Professional. After working in and leading many of the functional areas of the company, Darren is now focused on highly strategic programs and leverages his knowledge and experience to guide and develop employee-owners throughout the organization. For more than 35 years, Melink has helped commercial building owners improve the health, comfort, and energy impact of their facilities across the U.S. and world.