Test Reports: JB Engineering and Code Consulting, P.C. had the General Plastic duct fittings tested by SGS U.S. Testing Company, Inc., Tulsa, Oklahoma. The test report numbers and dates are, as follows:
Report No. 109962-1, dated 7/9/98 by SGS U.S. Testing Company, Inc.
Report No. 109962-2, dated 7/9/98 by SGS U.S. Testing Company, Inc.
Report No. 109962-3, dated 7/9/98 by SGS U.S. Testing Company, Inc.
Report No. 109962-4, dated 7/9/98 by SGS U.S. Testing Company, Inc.
The first test was an external loading test conducted in accordance with Section 6.3.2 of ASTM D2665. This test requires pipe fittings to withstand a load of 750 lbf/ft without failure. Fittings of every size were tested. All of the fittings passed the test without any signs of failure.
The second and third test were cell classification tests for rating the raw material used to produce the fittings. The PVC had a cell classification of 12344A. The HDPE had a cell classification of 33663.
The fourth test was a pressure tightness test. A 6 inch duct assembly was joined in accordance with the manufacturer's installation instructions. The assembly was subjected to a 4 foot head of pressure (1.7 psi) on the exterior. There was no leakage present in the assembly.
Analysis: Plastic duct and fittings are well suited for underground installation. The material is resistant to corrosion and rusting. The duct will provide a long, usable life as a part of the HVAC system.
The joining method of plastic duct and fittings is watertight and airtight for the normal pressures anticipated in an HVAC system. The duct will provide service without outside leakage when completely exposed to ground water on the exterior of the duct system. The duct is buried below the slab, hence, it would not be subjected to a ground water pressure that would approach the tested 4 feet of head pressure.
Report Number: 07G0516E1
May 16, 2007
Both PVC and HDPE are acceptable materials for temperatures up to 150E F. Standard furnaces and air handlers for HVAC systems limit the outlet temperature to less than 150E F. This would be required for any underground plastic duct system.
The smooth interior of the plastic duct has minimal friction resistance to air flow. The system can be sized using the round duct sizing charts and programs. The General Plastic duct fittings have a pattern and smooth interior that is equivalent to round duct fittings. The sizing charts and programs for the round duct fittings can be used when evaluating the plastic duct fitting for sizing the system.
In a comparative analysis, PVC plastic ducts are the same materials as PVC plastic pipe used below ground in plumbing systems. PVC plastic pipe has proven to be an acceptable material for underground piping systems. The material has been installed in the United States since the 1950's. Widespread use of PVC plastic pipe below grade dates back to the late 1960's. PVC plastic duct and fittings installed below grade should experience the same longevity as PVC plastic pipe used in plumbing systems.