Quieter HVAC Part-4

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

This is Part 4 of our 4-Part article — Describing Many Things You Can do To Have Quieter 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.

Newer DFW Homes

Image Source: Pixabay

(and other Cooling/Southern climates)

Have One Of These — for return-air to exit the bedroom (when the door’s closed).

• ducted air-return  (best)
• air transfer grille  (acceptable — though done as a cost-cutting measure)
• door undercut       (acceptable — with a large enough gap). **

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

Air-Transfer Grills With Honeycomb Insert

Will Create A Quieter HVAC System In Bedrooms

Many New Home Builders Simply Cut A Hole In The Wall & Add A Return-Air Grille (cover) On Each Side.

This Allows Noise & Light To Easily Pass Through.

If You Have Noise & Sound Transfer Issues — A Better Solution Is To Install An Air-Transfer Kit With Honeycomb Insert (shown below).

This Notably Reduces the Amount Of Noise & Light Entering The Room (when the door’s closed)..

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

Supply-Air Register(s)

Various Supply-Air Registers Meet Different Airflow Requirements.

• Some are designed to move air longer distances.
• Their louvers are closer together — to increase the air speed as it leaves the vent.   The one shown just below is this style.
• This style creates more air turbulence & noise.

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Shown: This Air Register Is Designed To Move Air Farther.  

Note the smaller gaps between the louvers.

• Some Supply-Air Registers are designed to move air short distances.   The one shown just below is this style.
• Their louvers are farther apart.
• This style creates less air turbulence & noise.

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Shown: This Vent Is Designed To Move Air a shorter distance.   

Note the larger gaps between the louvers.

A Solution For Noisy Supply-Air Vents

Registers designed to move air longer distances are sometimes installed — instead of having two registers in the room.  This is an acceptable method — but not optimal (it’s a cost-cutting measure).  If the air-movement noise isn’t an issue, there’s no need to make changes.  If the noise is too loud, the solution(s) below will remedy the problem.

NOTE: Changing the register (cover) with one that moves air a shorter distance(with can lead to a room that’s not comfortable.  In that case, a 2nd vent (on the same duct) needs to be installed.  Two ducts (with registers designed to move air short distances) — will be substantially quieter than one.  This is because the amount of air coming from each duct is 1/2 of what came from one duct.   The slower air moves, the less noise it creates.

• Use Supply-Air Registers designed to move air shorter distances.
• This Reduces Air Speed & Noise Generated.
• TIP: Changing register styles — may create a less comfortable room (because they don’t move air as far).

• Add An Additional Vent(s) — To That Ductwork Line.

Ductwork Noises

Image Source: Shutterstock

SHOWN: Metal Ductwork

Image Source: Shutterstock

Shown: Flexible Ductwork

• Metal ductwork is more likely to make noise than flexible dutwork (made mostly of vinyl).
• Most residential metal ductwork is made from thin sheet metal.
• This may lead to “booming”:  As the furnace blower turns on -OR- A few minutes later (as the metal warms up and expands).
• This may also lead to; ticking, rattles, and vibration.

Metal Ductwork Comes In 3 Shapes. 

Different Ductwork Shapes Create Different Amounts Of Air Pressure & Noise.

• Round ductwork is best (flexible ductwork is round).
• Square is good
• Rectangular is acceptable.  It’s more common because it’s less expensive.  Because it has 2 wide sides — those sides are more likely to make noises.

Metal Ductwork Noises — And Ways To Reduce or Eliminate Them

Booming

• A loud boom from the ductwork might be heard when the furnace blower turns on (from rapidly increased air pressure caused by the furnace blower).

OR

• Shortly after the furnace turns on (and the metal begins to warm up).

When The Furnace Blower Turns On — Metal Ductwork:

• May bow outward (from the rapid increase in air pressure caused by the furnace blower).
• May expand as it heats up.
• Either of these can cause a “boom”.

If You Can Locate Where The Metal Is Booming:

• Place your hand on various locations see if you can prevent the boom, it’s less loud.

• If so — install an expansion-joint (discussed just below) — close to the location of the boom.
• An expansion-joint — absorbs metal ductwork expansion.
• An expansion-joint typically includes a flexible, canvas duct connector.
• One is typically installed between the furnace and ductwork (shown just below).

NOTE: An Expansion Joint Can Be Added Anywhere Booming Occurs.

Image Source: YouTube Embedded Video

SHOWN: Installing A Flexible Ductwork Connector Between The Furnace and Ductwork.

Rattling

• Rattles are often due to loose metal ducts bumping nearby surfaces.
• Put your hand against the ductwork in various locations — to see if you can silence the rattle.

If You Can Find The Location Of The Rattle:

• “Cross-break” the metal.  This is done by adding a crease in the sheet-metal — with a flat screwdriver (details below).
• If cross-breaking doesn’t work — add an additional Ductwork-Hanger at the location of the rattle.
• Put self-adhesive felt dots between the new hanger and the ductwork.  They help absorb some ductwork movement — without making noise.

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Shown: Plastic Ductwork Hanger.   

Shaking or Vibrating

• A clogged air filter can cause ductwork shaking or vibrating.
• When an air filter becomes clogged — it creates a substantial air pressure increase in Return-Air ducts + a substantial air pressure decrease in Supply-Air ducts.
• The ductwork wasn’t designed or installed for air pressure increases/decreases so large.  This can lead to shaking or vibrating.

Ticking

• Ticking is typically caused by metal ductwork expansion (at beginning of heating cycle) & contraction (after heating cycle ends).
• Put your hand against the ductwork in various locations — to see if you can silence the rattle.

If You Find The Location Of The Ticking:

• Sometimes, the ductwork is rubbing against adjacent wood inside the wall.

If You Can Get To The Ductwork At the Location Of The Ticking:

• Install self-adhesive felt pads between the wood and ductwork.
• “Cross-break” the metal — by adding a crease in the sheet-metal with a flat screwdriver.

• The YouTube video (shown below) — demonstrates how to crossbreak metal ductwork with a screwdriver.
• Note:  You can likely do this with the ductwork installed.

NOTE:  The Image Below — Is A YouTube Video Showing How To Cross-Break Metal Ductwork. 

Rumbling or Popping

• IF air pressure within the system is correct — these sounds are due to the sheet-metal movement.

• Rectangular, sheet-metal ductwork is often the source of ductwork popping.
• Because it has 2 wide sides — there’s more metal expansion/contraction on the wide sides.

• FIX: “Cross-break” the metal — by adding a crease in the sheet-metal with a flat screwdriver (details just below).

NOTE: The YouTube video just below demonstrates how to do cross-breaking.

NOTE: This can be done to metal ductwork that’s already installed.

• Cross-breaking stiffens & strengthens sheet-metal.
• This reduces or eliminates several noises caused by sheet-metal movement.

Source: https://bass-air.com/2015/01/18/duct-and-furnace-noises/

• If ductwork is pressing against wood — install rubber pads between the ductwork and.

Insulate Ductwork

• Helps reduce expansion & contraction.
• Reduces the volume of ductwork noise.
• Lowers heating & cooling costs
• Reduces the time needed for heated/cooled air to be felt at the vent.

In Some Cases — Noisey Ductwork Must Be Replaced In Order To Have A Quieter HVAC System. 

• Replace metal ductwork with flexible/vinyl ductwork.

Replace Metal Ductwork With A Different Shape And/Or Metal Thickness.  

• Round is best.
• Square is 2nd.
• Rectangular is last.

• Replace ductwork with thicker sheet metal.

A High-Efficiency Furnace Provides A Quieter HVAC System

Furnace Noises

• Many furnace noises are normal and to be expected.
• Other noises may be an indicator of a problem with the HVAC System.

Today:

• Furnaces installed in the northern U.S. must be 90% efficient (or higher).
• With these, you’ll hear less noise from the exhaust-venting motor.
• With these, you won’t hear the burners ignite.

Image Source: CanStockPhoto

Shown: 90% (or higher) Gas Furnace.  Note the 2 white PVC pipes (one is at the right edge of photo).

90%+Efficient Furnace Noises

90% Furnaces Provide A More Quiet HVAC System.

• 90% furnaces have an outside-air intake (PVC) pipe.
• 90% furnaces have a (PVC) pipe that takes the exhaust to outdoors.

• Their combustion chamber is sealed.
• You hear very little noise (if any) from the burners.
• You hear limited noise (if any) from the fan that moves the exhaust gasses.

You’ll Likely Hear 1 Sound With A High-Efficiency (90% or higher) Furnace

• The blower fan motor.

• Southern U.S. furnaces can be 80% efficient (or higher(.
• 80% of furnaces make notably more noise than 90% or higher.
• This is primarily due to vent holes in their front cover (see 2nd photo below).
• The open front allows noise to be heard from the exhaust-venting motor and burners.

Image Source: CanStockPhoto

NOTE: Air Vents Are Visible In This Furnace’s Front Panel

Shown: 80% (or lower) Efficiency Furnance

NOTES:

• 80% Furnaces Have Holes In Their Front Panel.
• Combustion-Air For The Burners Enters Through These Holes.

These 3 Noises Occur Each Time An 80% Furnace Goes Through A Heating Cycle.

• 1st: A small fan (called an inducer) — that moves exhaust gasses up the flue.
• 2nd: The burners lighting.  This sounds like a low-volume “swoosh”.
• 3rd: The blower fan motor.

In DFW:

• Many homes’ furnace is in the attic.  It’s unlikely that noise from the furnace is an issue.
• Some home’s furnace is within the living space.  Furnace noises can be an issue with this location.

TIP:  If noise from your existing furnace is an issue.  When installing a new one — choose a 90% (or higher) for notably less noise.