How To Have A More Quiet HVAC System – Part 3 (of 3)

Click Here For Part 1 Of This Article: AlsPlumbing.com Make HVAC System Quieter

This is Part 3 of our 3-Part article — Describing Many Things You Can do To Have A More Quiet HVAC System.  Al’s Plumbing, Heating & A/C, in Plano, Texas provides full-service plumbing maintenance, repairs, and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s Plumbing, Heating & A/C is near your home in McKinney TX; Allen, TX; and Plano Texas. We service all homes in southern Collin County, TX & northeastern Dallas County, TX with no additional travel charge.

Another Common Source Of HVAC System Noise Is

1 Central Return-Air Duct (serves the entire house).

(More Air Flow At 1 Location = More Noise)

Shown: 1 Central Air Return Grille.  These Are Quite Large — Because They Serve The Entire Home.

There Will Be Notable Noise Near This Grille — Because ALL Air (returning to the furnace) Passes Through It.

Central air returns are common in newer homes.  Instead of providing an air-return in each room (except kitchen and baths) — only one return is installed.  It’s an acceptable (but not optimal) way to configure an HVAC System — it’s done as a cost-cutting measure.

• The location of this return-air duct may create a noise problem.
• If it’s in a hallway or foyer, the noise is less likely to be an issue.
• If it’s near bedrooms, or a room where TV is viewed — it can be a nuisance.
• Each time the HVAC System turns on or off — the TV’s volume must be adjusted.

• Just Below — we discuss several ways to reduce the noise created by a 1 Central Air-Return.
• These same efforts can also be used on single-room returns as well.
• In some cases, the only real solution is to relocate the return-air duct.

Definitions

• Supply-Air Duct (brings air from the furnace). 
• Its cover is called a: “Register”. 
• It has a louver/damper to control airflow.
• In DFW — most are in the ceiling because ductwork is commonly in the attic.

• Return-Air Duct (takes air to the furnace). 
• The one shown just above is a single-room air return.
• Its cover is called a: “Grille” 
• These smaller air-returns are located in every room (except kitchen & baths) — and serve only 1 room.
• This is the better way to provide Return-Air to the furnace.
• No shut-off louver.
• Return-Air ducts are never to be shut off.

• Central Return-Air Duct (takes air to the furnace).  
• The one shown just above is a Central Air Return that serves the entire house.
• Its cover is called a: “Grille”  
• Central return air ducts create notable noise — due to the amount of air movement at 1 location.

• It’s also common for the central return air duct to be located directly below/ above the furnace.  Especially if the furnace & ductwork are in the attic.
• This configuration also allows the furnace’s operating-noises to be heard.

Click Here To See A Central Return-Air Duct Below Furnace (furnace located inside the home).

Click Here To See A Central Return-Air Duct In A Ceiling (furnace located in attic)

There Are 2 Sources Of Noise Coming From Every HVAC System:

Resolve Some Of The Issues Below — And You’ll Have A More Quiet HVAC System

• Operating Noise: Is made by HVAC components.
• Most Indoor Noise comes from the furnace’s blower + the ductwork.
• 80% efficient furnaces (allowed in the southern U.S.) — you may also hear; the exhaust-venting motor & burners igniting.
• 90% efficient furnaces (required in the northern U.S.) — you won’t hear; the exhaust-venting motor or burners igniting.

• Airborne Noise: Is created by moving air.
• TIP: Noise travels through the air.  Where you hear the noise may not be where it originates.

TIP: Closing off more than 10% of Supply-Air Ducts increases air-pressure throughout the ductwork.  More air-pressure = more noise.

An Expensive Way To Have A Quieter HVAC System.

• Note: 90%+ of HVAC Systems are single-speed.
• Replace an existing HVAC System with a Variable-Speed System.
• A Variable-Speed Furnace Blower adjusts its speed — based on the amount of air-flow the ductwork configuration and settings can currently accommodate.
• This allows as many supply-air vents (to be closed) — as the homeowner desires.
• With a single-speed HVAC System (90%+ are single speed) — no more than 10% of ducts can be closed without adversely affecting HVAC System performance.

Low-Cost Ways To Reduce Central Air-Return Noise

TIP: Combining Solutions May Further Reduce Noise.

1. Replace The Return-Air Duct’s Grille — With One That Holds An Air Filter.

If You Have A Central Air-Return Duct — This Is The Easiest Way To Have A More Quiet HVAC System.

It’s often possible to replace the existing Return-Air Grille with one that holds a filter.   TIP: It’s OK if the new grille is larger than the ductwork’s opening.

• The filter at the grille helps muffle noise.
• This also eliminates going into the attic to change filters.

Image Source: Amazon.com Embedded Link

Click On Image To; View Product, See Details, or Purchase From Amazon.com

Shown:  Return-Air Filter Grille

2. Change The Central Return-Air Grille To Eggcrate Style

The More Obstructions A Return-Air Grille’s Cover Has — The More Air Turbulence & Noise It Will Generate.

Egg-Crate Return-Air Grills Come In Many Sizes –The One Shown Below Is 24″ X 24″.

The Company That Sells This One — Has 10 Sizes Available.

NOTE: The Benefit Of Eggcrate Return-Air Grilles Is Their Desing Minimizes Air-Flow Restriction.

Thus more air-restriction(s) — the more (air movement) noise is generated.  

Image Source: Amazon.com Embedded Link

Click On The Photo To; View Product, Read Details, or Purchase From Amazon.com

SHOWN: 24X24 Inch Central Return-Air Grille

NOTE: On Amazon — This Particular Product Is Rated At 4.5 (out of 5).  When This Was Written — There Were nearly 850 Reviews.

3. Line The Return-Air Ductwork (that you can easily get to) With A Sound-Deadening Material.

Image Source: Amazon.com Embedded Link

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SHOWN: Noise Insulation (Sold in either 10 or 18 Square Feet)

(22 mm of Butyl Rubber (odorless & synthetic) — With A Foil Surface).

NOTE: On Amazon — This Particular Product Is Rated At 4.7 (out of 5).  There Were Nearly 5,200 Reviews (when this was written).

This Product’s Noise-Reduction Expectation — Base On Scientific Studies (Links Provided):

Foil-Faced + 2 mm of Butyl Rubber — Reduces Noise By Nearly -5.5 db.

That’s -25% less noise (volume) — as perceived by our ears.  NOTE: This Is Based On: -10 db = -50% of the noise volume — as perceived by our ears.

SOURCE: https://www.soundproofcow.com/soundproofing-101/how-to-soundproof-a-home-2/how-to-soundproof-hvac-systems/

SOURCE: https://www.sciencedirect.com/science/article/pii/S2211379719314445

4. Sometimes The Duct Can Be Made Larger. 

• A larger opening duct allows for slower air-movement speed.
• A larger duct creates less air flow restriction.
• Slower moving air makes less noise.

5. Add An Additional Air-Return Duct.

• An additional return-air duct can often be installed.
• In some cases, it can be connected directly to the existing return-air ductwork.
• Two openings (on the same duct) — reduces the amount of air movement at each opening.
• Less air movement = less noise at each duct.
• A second return air duct — is best installed where noise is less of an issue (such as a hallway or foyer).

Older DFW Homes

Return-Air Pathway From Bedrooms (when the door’s closed)

Many older DFW homes also have central air returns.  Unlike newer homes, in older DFW homes, return-air from bedrooms must pass under the door.  In newer DFW homes, an “air-transfer grille” is installed above the door (eliminates the need for air to travel under the door).   With DFW being a cooling-climate, an opening above the door is preferred.

Older DFW Homes’ Return-air (coming from bedrooms) — passes under the door (when the door’s closed). 

• A 1/2″ gap, between floor coverings and door — allows for return-air to exit the bedroom when its door is closed.
• If thick carpet & pad are present — the gap under the door is often too narrow.
• This reduces the HVAC System’s ability to properly heat & cool bedrooms (when the door’s closed).

TIPS: 

• If there is less than a 1/2″ gap between bedroom doors & floor coverings — one solution is to cut bedroom doors shorter.
• Creating a larger gap (>1/2″) isn’t needed, nor wise.
• A larger gap allows light to enter under the door — plus privacy & noise concerns may arise.

For Souther/Cooling Climates

A Better Solution: Install A Retrofit Air-Transfer Kit Above Bedroom Doors.

This Is Because Removing Warm Air During Summer — is more of an issue than removing cold air in winter.

Image Source: Amazon.com Embedded Link

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SHOWN: Honeycomb-Style Air-Transfer Kit (includes the 3 parts shown)

NOTE: The Reason We Show The Honeycomb-Style Air-Transfer Kit — is because they reduce the amount of noise and light that can enter the room (when the door’s closed) — as compared to simply cutting a hole and putting a grille on each side.

Copy The Link Below Into Your Browser To See An Air-Transfer Grille Installed Above A Bedroom Door:

https://basc.pnnl.gov/resource-guides/transfer-grilles

NOTES:

• Most bedroom doors are 32″ wide.
• There’s typically a (vertical) piece of lumber centered within the space above the door.
• Avoid removing lumber inside walls.  It’s there to support the weight of the house.

TIP: Buy An Air Transfer-Grille That’s 14″ Wide Or Less — so it can fit on either side of the vertical piece of lumber

NOTE: For Older Homes In Heating/Northern Climates

If A Bedroom Doesn’t Have An Air-Return.

Because Our Articles Are Written For The Dallas-Ft Worth Texas Area — Our Focus Is For Homes In Southern/Cooling Climates.

In this case —  we also include a better solution for heating/northern climates’ bedrooms (than cutting doors shorter).  This is because the Air-Transfer Grille shown below reduces the amount of noise and light that can enter the room (when the door’s closed) — as compared to cutting doors shorter.     It’s notably easier to cut the doors shorter — if noise & light entering the bedroom(s) isn’t an issue.

A Retrofit, In-Door, Air-Transfer Grille — Designed Designed To Be Installed In The Door (NO Honeycomb Insert). 

18″ Wide X 5″ Tall. 

Image Source; Amazon.com Embedded Link

Shown: In-Door Air Transfer Grille (includes both sides as shown).  Also available in white.

Click On Image To; View Product, Read Details, or Purchase From Amazon.com

NOTE: There Is No HoneyComb Insert For This Product.

A Retrofit, In-Door, Air-Transfer Grille — WITH Honeycomb Insert

27″ Wide X 4.75″ Tall. 

This product is more expensive than the one shown above.

Because It Has A Honeycomb Insert (to reduce noise & light transfer into the bedroom) — Plus It’s Wider.

TIP: A Honeycomb Insert Notably Reduces Noise & Light Transfer Into The Bedroom.

Shown: In-Door Air Transfer Grille (includes both sides as shown + Honeycomb Insert).  Also available in white.

This Item Rated 4.5 Stars (out of 5) — With 315 Reviews (when this was written).

Click On Image To; View Product, Read Details, or Purchase From Amazon.com

NOTE: HoneyComb Insert Included With This Product.

NOTE: This Product Comes In Various Quantities.  To Buy 1 — click on the appropriate box.

TIP: Air Transfer Grilles Designed For Walls — Are Too Thick For Doors. 

TIP: Air Transfer Grilles Designed For Designed For Doors — Are Too Thin For Walls.