Fiberglass lined HVAC duct (C) Daniel Friedman Guide to HVAC Duct Sound Control in buildings

  • SOUND CONTROL for AIR DUCTS, HVAC - CONTENTS: Principles of heating system or HVAC sound transmission in buildings. How to make a building quiet: blocking heater or air conditioner or duct noises. Sound insulation designs for building mechanical systems. Sound control for building boilers, furnaces, ducts, pipes, and mechanical rooms.
  • POST a QUESTION or READ FAQs about sound or noise transmission through HVAC ductwork
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Noise & sound control for air conditioning or heating system ductwork:

This article explains methods and materials used to control heating, ventilation, and cooling duct noises and sound transmission in buildings: how to make a quiet home, office, or place of business using sound isolation for ceilings, floors, walls, plumbing, etc.

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HVAC Duct Insulation Options for Soundproofing & Noise Reduction in buildings

Fiberglass duct insulation (C) Daniel Friedman

Our page top photo shows a typical fiberglass lined HVAC duct interior. The gray debris stuck to the fiberglass is usually house dust, comprised chiefly of skin cells and fabric fiber. Sometimes more troublesome debris collects on interior HVAC duct insulation.

Our building sound control articles begin at SOUND CONTROL in buildings. Other noise and sound diagnosis and control articles are found at NOISE / SOUND DIAGNOSIS & CURE.

As stated in Best Practices Guide to Residential Construction: Use fiberglass ductboard or fiberglass duct liners to quiet the noises of fans and moving air. Avoid sharing a common duct between two rooms that need sound privacy.

Elaborating on some duct insulation considerations: HVAC experts advise us that conventional practice is to insulate the interior of metal ductwork in order to minimize transmission of HVAC equipment sounds throughout a building.

Some fiberglass duct liners are plastic coated and may be able to be cleaned using gentle procedures.

But most common is the use of un-faced fiberglass duct interior insulation, typically treated with a surface resin binder to help reduce movement of fiberglass particles into the air stream.

Our fiberglass lined duct insulation photo (left) shows clean new metal ductwork with a pink fiberglass mat sound and temperature insulation installed on the duct interior. Our page top photo shows that building dust and debris quickly adheres to fiberglass interior duct insulation.

Fiberglass board duct construction (C) Daniel Friedman

However our work on indoor environmental and air quality topics suggests that from an indoor air quality maintenance view, we prefer to see insulation on the exterior of metal ducts.

That approach permits the ducts to be cleaned, and it reduces the chances of mold growth in the ductwork.

See DUCT SYSTEMS and see HIDDEN MOLD in OTHER PLACES for more about places to look for duct system defects and hidden mold on HVAC systems.

Mold in Fiberglass Insulation illustrates problem mold growth in fiberglass insulation including in duct systems.

Construction of HVAC ducts from foil-faced insulating board (photo above left) combines sound and temperature insulation with aluminum foil to product ductwork that is quiet and cleanable using gentle methods.

Other steps to reduce HVAC system duct noise in buildings include:

Furnace in closet (C) Daniel Friedman

  • Proper HVAC duct mounting and routing to avoid tight contact with floor framing without use of sound isolating mounts
  • Selection of the proper air handler blower size and speed
  • Location of the air handler unit away from occupied space; if constructing a sound-isolated framed-in enclosure for an air handler for heating systems that burn fuel (LP gas, natural gas, oil, wood) be sure that your soundproofing does not prevent provision of safe and adequate combustion air.

    An outdoor combustion air supply can permit near total isolation of HVAC equipment from the rest of the building.

Our photo (left) shows a furnace mounted in a mobile home closet. Owners, in an attempt to reduce furnace noise in the adjacent living space, closed off the return air inlet by installing a solid door. Heating output was substantially reduced and heating costs increased by this bad practice.

-- Adapted with permission from Best Practices Guide to Residential Construction.

Other Heating or Air Conditioning Duct Noises

A loud BANG or THUD or CLUNK heard when the heating or air conditioning blower fan starts or stops is often due to inadequate return air, to overpressureizing of the supply plenum at fan start-up, or it may occur where large areas of un-supported sheet metal are used in the duct system or air supply or return plenums. The problem may be more acute where a multiple speed or high speed blower fan is in use.

For hissing and howling HVAC duct system noises see


Continue reading about methods for sound control in buildings by using the links provided just below.

Building Sound & Noise Control Articles

Continue reading at HEATING SYSTEM NOISE DIAGNOSIS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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