HVAC seasonal checklist


Relative humidity should be monitored in all areas of the building, as an indicator of moisture problems. Moisture problems can occur in commercial buildings when there is uncontrolled airflow between conditioned and un-conditioned spaces within the building or between outside air and conditioned space. Uncontrolled airflow can occur wherever there is a leak or break in the air barrier of the building (around pipes, at wall and roof connection points, etc.). When there is a leak or break in the air barrier, any unbalance in the airflow associated with the HVAC system can result in significant airflow into or out of the conditioned space. When the unbalance creates a lower (negative) pressure in the building than that outside the building, then external un-conditioned air, which can be moisture laden in summer or high humidity conditions, is drawn into the wall or roof cavities where the moisture condenses on surfaces that have been cooled by air conditioning.

  • Check the HVAC system balance regularly to ensure appropriate pressures and airflow.

  • Check HVAC response to thermostats, humidistats, and other control systems regularly.

Here are some common causes of negative pressure and common solutions:

  • Insufficient return air supply

    • Common solution: adjusting dampers, installing vents in walls or doors.

  • Improper balance of ventilation and exhaust systems (combustion appliance venting, laboratory fume hoods, kitchen exhaust, etc.)

    • Common solution: add appropriate air makeup and conditioning measures.

  • Supply duct leaks

    • Common solution: taping or sealing joints in ducts.


  • Inspect your HVAC air filters monthly, or as recommended in the Operations and Maintenance manual. If you don’t know how to access the filters, refer to the manual for your specific unit.

  • When dust and debris are present, replace the filter with an identical filter as recommended by the manufacturer. If the filter is reusable, be sure it is completely clean and dry before reinstalling. Depending on its size, the equipment may have multiple filters that should be inspected or replaced.

  • Inspect all condensate drains and drain pans monthly, especially if your building must provide cooling most of the year. Refer to the maintenance book when inspecting drains and drain pans.

  • Check drain pans to insure they drain freely, are adequately sloped toward the outlets and that no standing water is present.

  • Make sure drain lines are clean and clear of obstructions.

  • If dirt, algae, or other contaminants are found, the drain line should be flushed and the drain pan carefully cleaned (pour a water-bleach solution down the drain line until it flows freely).

  • Inspect for signs of rust, which could indicate a water problem and need for prompt repair.

  • If the line drains to the outdoors, ensure that drainage travels away from the structure.

  • If the condensate drain is located on the roof, check that the drain is not clogged.

  • Rooftop drains should never drain directly onto the roof or over the side of the building.


  • Condensate drain pan overflows frequently occur the first time the unit is turned on in the spring because dust and dirt have accumulated over the winter months. However, overflows can occur any time the drain becomes plugged to the extent that the condenser removes water from the air faster than the drain line discharges the water.

  • Clean prior to first use with compressed air or by pouring a water-bleach solution down the drain line until it flows freely.

  • A float cutoff switch that will shut down the system if the pan doesn’t drain properly is a great safety feature that can prevent a flood from the overflowing drain pan.

  • Inspect ductwork seasonally for cleanliness, insulation, and tight connections.

  • Fresh air supply ducts must be kept free of debris and, if necessary, filtered at the inlet.

  • Inspect filters and ductwork to ensure adequate fresh air supply.

  • Make immediate repairs at the first sign of condensation or rust. Any rust, condensation, or other signs of moisture on ductwork can be a sign of a serious water management problem.

  • Furnace burners should be inspected at the beginning of each heating season, and regularly throughout the heating months.

  • Visually inspect the flame, which should be blue with a light yellow tip. If the flame is not this color, or, if the heating unit does not ignite promptly, contact an experienced HVAC professional.

  • Regularly check combustion gas exhaust components (chimneys, vents and connective pipes) to ensure proper venting of combustion byproducts.

  • Check the heat exchangers seasonally.

  • Cracked heat exchangers can create health, safety and water management problems. If checking these items is beyond the skills of your maintenance staff, be sure your HVAC professional is experienced in combustion appliance operation and safety.

  • Check for backflow of combustion gasses, carbon monoxide levels and other indicators of improper heating system performance.


  • All air coils should be inspected annually, at minimum, to confirm that equipment is operating at maximum capacity.

  • Follow the manufacturer’s instructions to obtain access to the air coils.

  • Coils should be cleaned of dust and debris by careful brushing or vacuuming, to avoid damaging the coil fins.

  • Keep outdoor condensing units clean from grass clippings and other debris.

  • Condenser units must remain level in order for water to drain properly.

Many modern HVAC systems are complex and require the skills of a trained professional. If your on-site maintenance staff is not fully familiar with HVAC systems, hire a professional before you are faced with a system failure or water management crisis.



Published 2009