Heating, Ventilation and Air Conditioning (HVAC) system should provide proper air flow, heating, and cooling to each room.




  • HVAC system should be properly sized to provide correct air flow, and meet room-by-room calculated heating and cooling loads.
  • HVAC system should be installed so that the static air pressure drop across the handler is within manufacturer and design specifications to have the capacity to meet the calculated loads.
  • HVAC system should have sealed supply ductwork that will provide proper air flow.
  • HVAC system should be installed with a return system sized to provide correct return air flow.
  • HVAC system should have sealed return ductwork that will provide proper air flow to the fan, and avoid air entering the HVAC system from polluted zones (e.g., fumes from autos and stored chemicals, and attic particulates).
  • HVAC system should have balanced air flows between supply and return systems to maintain neutral pressure in the home.
  • HVAC system should minimize duct air temperature gain or loss between the air handler and room registers, and between return registers and the air handler.
  • HVAC system should be properly charged with refrigerant.
  • HVAC system should have proper burner opersation and proper draft.



The following are minimum materials specifications recommended to achieve a substantially tight installation that will last:

  • All materials shall have a minimum performance temperature ratings per UL181 (ducts), UL181A (closure systems for rigid ducts), UL181B (closure systems for flexible ducts) and/or UL 181BM (mastic);
  • Shall have a flame spread rating of no more than 25 and a maximum smoke developed rating of 50 (ASTM E 84)




Factory-Fabricated Duct Systems

  • All factory-fabricated duct systems shall include UL 181 listed ducts with approved closure systems including collars, connections and splices;
  • All pressure-sensitive and heat-activated tapes used in the manufacture of rigid fiberglass ducts shall be UL 181A listed;
  • All pressure-sensitive tapes and mastics used in the manufacture of flexible ducts shall be UL 181B (tape) or UL 181BM (mastic) listed.

Field-Fabricated Duct Systems

  • Ducts: Factory-made ducts for field-fabricated duct systems shall be UL 181 listed.

·         Mastic sealants and mesh:

o    Sealants shall be UL 181BM listed, non-toxic, and water resistant;

o    Sealants for interior applications shall pass ASTM tests C 731 (extrudability after aging) and D 2202 (slump test on vertical surfaces);

o    Sealants and meshes shall be rated for exterior use;

o    Sealants for exterior applications shall pass ASTM tests C 731, C 732 (artificial weathering test), and D 2202.

·         Pressure-sensitive tapes:

o    Pressure sensitive tape shall be that recommended by and meet the requirements of the flexduct manufacturer;

o    Tape used for duct board shall be UL 181A listed and so indicated with a UL 181A mark or aluminum-backed butyl adhesive tape (15 mil. minimum).


·         Drawbands:

o    Shall be either stainless-steel worm-drive hose clamps or uv-resistant nylon duct ties;

o    Shall have a minimum performance temperature rating of 165 degrees Fahrenheit (continuous, per UL 181A-type test) and a minimum tensile strength rating of 50 pounds;

o    Shall be tightened as recommended by the manufacturer with an adjustable tensioning tool.


The following are design, fabrication and installation guidelines, that should be followed, which will provide a duct installation that is substantially airtight:

General Issues

  • Ducts, plenums, and fittings should be constructed of galvanized metal, duct board, or flexible duct. Building cavities may not be used as a duct or plenum without a sealed duct board or metal liner.

·         The air handler box should be air-tight;

  • Air filters should be easily accessible for replacement, and evaporator coils should be easily accessible for cleaning;
  • Ducts should be configured and supported so as to prevent use of excess material, diameter prevent dislocation or damage, and prevent constriction of ducts below their rated;
  • Flexible duct bends should not be made across sharp corners or have incidental contact with metal fixtures, pipes, or conduits that can compress or damage the ductwork;

·        Sheet metal collars and sleeves should be beaded to hold drawbands.


  • For systems with fixed metering devices use, evaporator superheat method:

o    Indoor coil airflow must be greater than 350 cfm/ton;

o    Refrigerant system evacuation must be complete (all non-condensables must be removed from the system;

o    In hot, dry climates be cautious to be within range of superheat charging chart or use a different method.

·         For systems with thermostatic expansion valves, use the subcooling method.




·         Check each chamber for correct flame;

·         Check for proper drafting.



The following are testing requirements and procedures that must be followed to ensure that the HVAC system has been properly installed. The tests are designed to determine whether:

1.    Total supply is as designed;

2.    Total return = total supply;

3.    Ducts Room-by-room air flows are correct;

4.    Ducts, plenum, and air handler are tight;

5.    Static pressure is correct.

Test the system to ensure that it performs properly, by (1) verifying HVAC equipment sizes installed are those specified, (2) measuring duct leakage, and measuring either (3) fan flow or (4) supply and return flows and plenum static pressures:

1.    Air conditioner sensible capacity must be no more than 15% greater than the calculated sensible load; fan flow must be greater than 350 cfm/ton; check that the correct size air handler is installed.

2.    Ensure that the duct system does not leak substantially:

·        A rough system, including both supply and return but without the air handler, should not leak more than 0.03*conditioned floor area (ft2) per system measured in cfm @ 50 Pa;

·        The finished installation, including supply, return, the air handler and finished registers, must not leak more than 0.07*conditioned floor area (ft2) per system measured in cfm @ 50 Pa;

3.   Measure air handler air flow and static pressure across fan; ensure that total air handler output is within 5% of design and manufacturer specifications at a static pressure within 0.1 in wg of design.

4.   Supply and return air flow, and static pressure requirements: Ensure that supply and return flows are correct, and that the static pressure across the fan is correct:

·        Measure room-by-room air flows to ensure that each register is within 15% of Manual D design air flow, and that the entire supply is within 5% of design;

·        Measure return air flow to ensure that it is within 5% of the total supply air flow;

·        Test static pressure drop across the blower to ensure that it is within 0.1 in wg of design and manufacturer specifications.

·        Duct leakage can be determined using a pressurization or depressurization technique; for details, see Minneapolis Duct Blaster? manual, or other commercially available duct pressurization or depressurization devices;

·        Duct leakage to unconditioned space can be determined with the house pressurization or LBL simplified technique; for details see California Energy Commission report P400-91-031CN, Section Six;

·        Fan flow, supply flow and return flow measurements, see Minneapolis Duct BlasterTM manual (or equivalent); alternatively for supply and return flows, use a calibrated flow hood. Do not use a pitot tube, or any type of anemometer to determine these air flows;

·        Static pressure drop across the fan is measured using a small probe in the return plenum and in the supply plenum.