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 Plano, Allen, and Frisco.  We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge. We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge.

Al’s also provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally, we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).


How To Make Your HVAC System More Quiet

Some HVAC System Noise Is Normal And Can’t Be Stopped

The common & normal noise you’ll hear from an HVAC system is a low volume, continual hum of properly functioning equipment.  When the system is running, you may hear the blower fan in the furnace, depending on where it’s installed.   It’s also typical to hear a low volume, swooshing sound of air coming from the vents.   The outdoor unit has a fan and motor that make more noise than indoor equipment.   It’s possible you will hear the outdoor A/C unit inside the house, particularly in a room located near the unit.

The two most common places for the furnace in a Texas home are in the attic, or within the living space in a hallway.  When the furnace is in the attic, much of the noise it generates cannot be hear inside the home’s living space.   This is because the noise must pass through the attic insulation.

If you are hearing your attic furnace, how much attic insulation do you have?  Texas Building Code Requires R-38 Attic Insulation.   Using the chart below, you can determine the      R-Value of your attic insulation.  If it’s below R-38, the cost to cool & heat your home is notably higher, and added insulation would pay for itself over time.   Also if it’s below R-38, more of your furnace’s noises are passing through the insulation & ceiling into the living space.  More insulation will also help reduce air-traffic noise, highway & road noises, and other environmental noises.

Approximate R-Values Per Inch, By Type Of Attic Insulation**


  • R-2.2-2.9  Fiberglass
  • R-3.1-3.8  Cellulose (created by chopping & fire-treating recycled newspaper)
  • R-2.2–3.3 Rock /Stone / Mineral Wool  (created by spinning molten rock & minerals with steel slag (a by-product of molten iron processing) to create a cotton-candy density wool product.


  • R-2.9–3.8 Fiberglass
  • R-3.0–4.2 Stone / Mineral Wool
  • R-2.0–3.9 Cotton

Spray Foam:

  • R-3.5–3.36 Open-Cell Polyurethane Spray Foam.  The type of foam allows water-vapor to pass through (does not stop moisture).
  • R-6.0–6.5 Closed-Cell Polyurethane Spray Foam.  This type of foam does not allow water-vapor to pass through (stops moisture).

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The Most Common Reasons An HVAC System Makes A Lot Of Noise

Too Many Room Vents Are Closed

NOTE: If your HVAC System has a Variable-Speed Furnace Blower Fan, this does not apply to you.

If your HVAC System is Single-Speed (90% of systems are), when you close a vent, it increases air pressure inside the ductwork.  The causes faster air movement through the ducts that are open.  The more ducts you close, the more noise your HVAC System will generate, due to higher air speed through the open vents.   Closing off more than 1 or 2 vents is not recommended with any Single-Speed HVAC System.  it was designed and installed to be operated with all the vents open.

NOTE: If you have a variable speed HVAC System, it will slow the furnace blower fan to ensure correct air velocity through the open ducts.  It also reduces the amount of cooling or heating the system is creating to match the furnace blower fan speed.

Dirty Furnace Air Filter

dirty air filter on left. New air filter on right.

Image Source: CanStockPhoto

SHOWN: Clogged Air filter – On The Left.  New Filter – On The Right.  

The dirtier your filter gets, the harder the furnace blower fan must work to force air through the filter.  This causes pressure on the blower fan which causes it to make more noise as it works to force air through a dirty air filter.   Check and change (if needed) your furnace air filter each month.  Do it on the first day of the month and it will become easier to remember.   If the filter looks dirty, it is, and it needs to be replaced.  A dirty air filter increases cooling & heating costs by up to +15%!


One Central Air Return Duct

Shown: A Central Air Return Grill Will Be Quite Large Because It Serves The Entire Home.


  • Supply Air Vent — covers the vent where air is coming into the room.  It has a louver/damper to control air flow.
  • Air Return Grill covers a vent where air is being returned to the furnace.  Air returns don’t have louvers / damper and can’t be shut off.
  • Central Air Return grill serves the entire house.
  • Return Air Filter Grille is designed for an air filter to be attached directly to the grill.  These are often found in homes with the furnace in the attic.

Many homes are built with 1 Central Air Return Duct.  While certainly an acceptable way to build a home, a Central Air Return is a cost-cutting measure.  Homes with a single, central return air duct create a lot of noise at that duct due to the volume of air moving into and through it.   If your home has 8-12 air supply ducts, and only 1 central air return duct, the entire amount of air moving through the furnace is coming in from one location.  Also it’s common that this central return-air duct is directly below or quite close to the furnace.  This allows furnace noise to be heard through the duct too.

Click Here To See A Typical Central Air Return Grill 

If a home has a central air return duct, it’s typically quite large.  If the furnace is inside the living space, there is often a large return air duct quite close to the furnace, and sometimes directly below the furnace.

Click Here To See A Central Air Return Grill Directly Below Furnace

In home’s with several return air ducts, the ducts will be smaller.  There will typically be 1 return air duct in each room.  This system will operate more quietly.  The reason many homes are built with one return air duct is because it’s less expensive.

To solve the noise problem caused by having only 1 central air return vent, sometimes the duct can be made larger.  This will lower the speed of the air passing through it (because there is more area for the air to pass though).   The slower the air is passing through any duct (supply or return-air) the quieter the duct will be.

Most times solving this problem requires adding another return-air duct (perhaps more than one) to lower the air volume passing through a single return-air duct.  In some cases, additional ducts can be located in areas where noise is less of an issue (such as a hallway or foyer).

Return Air Filter Grille

TIP: If you must go into your attic to replace furnace filters, it may be possible to replace a Central Return Air Grill with one that allows a filter to be attached.  It must fit within the existing opening, and the opening must allow for a thicker grill (due to the filter) to slide into the hole.\

If you are able to replace the existing (no filter) grill(s) with one that allows a filter to be attached, it will no longer be necessary to have a filter inside the furnace.  It may be advisable to have one in the furnace too, though it would rarely need replaced (if at all).   With two filters, use the standard / cheapest air filter inside the furnace.  They typically have blue, coiled fiberglass.

Click Here To See This Type Of Filter: Basic Furnace Air Filter

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

Shown:  Return Air Filter Grill


Air Transfer Grills

In older homes, the return air from bedrooms passes under their door.   If thick carpet & pad are present, often times there is very little space under the door.  This causes increased air pressure inside the bedroom when the furnace is running.  It also hampers the HVAC System’s ability to properly heat & cool bedrooms because less air comes into a room where air cannot exit  properly.

TIP:  If there is less than a 1/2″ gap between the bedroom doors & flooring, one solution is to cut the doors shorter.   Cutting the door even shorter is not wise.  Light will enter a darkened bedroom under the door, plus privacy & noise concerns could arise.  The best solution is to install Transfer Grills above the doors (see details just below).

TIP: If adding transfer-grills, buy retrofit versions.  Other versions are often 24′ wide, and the lumber studs inside walls are typically spaced 18″ apart.  This would require needlessly cutting a lumber stud, and that’s not advisable when it can be easily avoided.

Shown: Retrofit Air-Transfer Grill

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

In newer homes the air passes through a “transfer grill” that is typically above the bedroom’s door.    Transfer grills allow air to be pulled from bedrooms when the door is closed.  There is a central return air that is open to the living space.   Transfer Grills are installed to prevent room pressurization caused by air being forced into the room with no place for air to exit.  Transfer grills cannot be closed off.  They are always to be open, to ensure a path for return air from the bedrooms.   Transfer grills work well in summer, as the warmest air in the room is removed through the transfer grill.  In winter, transfer grills don’t work as well (though acceptable).  as warmest air also leaves the room.

There are retrofit transfer grills made for doors.   Door transfer grills are intended to be installed near or at the bottom of the door.  With DFW being a cooling climate, transfer grills above the door would serve the home best.  Grills designed for walls are too thick for doors, and those designed for doors are too thin for doors.

Click Here To See An Air Transfer Grill Installed Above A Bedroom Door: Air Transfer Grill Installed

Not Enough Return Air Capacity

A common HVAC system complaint is that the return air vents make a high-pitched sound.  This is typically due to insufficient return airflow.  This causes the system to pull more air through the existing ductwork than it’s designed to carry.  This increases both air pressure & speed, both of which increase noise level.  By adding more return air vents, the system doesn’t have to work as hard and becomes quieter.

Restrictive Supply Air Register(s)

Supply Air Registers are made to meet various airflow needs.  For example, some are designed to move air long distances.  To accomplish this, these registers have louvers closer together (to increase air speed).  Again, the higher the speed of the airflow, the more noise will be created.

The solution – Replace these registers / vents with ones designed quieter operation.  The more open the face of the register / vent is, the less restriction on air-flow, and the quieter it will be.  Another solution may be to add an additional register with that particular ductwork line.  This cuts the air velocity in half, and makes it quieter.

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

Shown: This Air Register Is Designed To Move Air Farther.  It does this with smaller gaps that causes the air to move faster (and thus farther).


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

Shown: This “High Airflow” Register Is Designed To Move A Higher Volume Of Air (a shorter distance).   

It does this with larger gaps that allow the air to move more slowly.


Improperly Installed Flexible Ductwork

If flexible ductwork isn’t installed properly it tends to; sag, kink, flatten, or bend.  These problems make it harder for the HVAC System to move air, which causes it to create more noise.  If your HVAC system seems to have become notably more noisy recently; 1. Check your air filter first.  2. If the filter is new or clean, have a ductwork inspection performed.

Click Here To See Sagging, Flexible Ductwork Due To No Support Straps

Click Here To See Flattened Ductwork –  Due To Being Forced Into A Location Not Suited For It: Flattened Flexible Ductwork

Click Here To See Ductwork That Is Bent Too Much As A Result Of Being Poorly Installed: Excessively Bent Flexible Duct Work

Click Here To See PROPERLY INSTALLED Flexible Ductwork: PROPERLY Installed Flexible Ductwork


METAL Ductwork Noises, And Some Causes

  • Some ductwork is more prone to noise than other types.
  • Metal ductwork is more likely to make noise than flexible.
  • Metal ductwork is found in three shapes; round, square & rectangular.
  • The shapes don’t handle air pressure equally.  Round ductwork handles air pressure best (flexible ductwork is round).  Next is square, and then rectangular.  The rectangle has 2 short sides & 2 long sides, and the long sides are what makes the noises.
  • Most residential ductwork is made from thin sheet metal.

Common Ductwork Noises, And What May Be Causing Them:

  • Rattling: Caused by loose metal ducts knocking against each other.
  • Popping, Banging & Ticking: Caused by expansion of the metal ductwork when the furnace runs.  In summer, if contraction occurs while the A/C is running.
  • Shaking or Vibrating: When an air filter becomes clogged, a substantial air pressure drop occurs.  This can cause ductwork to shake, knock or vibrate.
  • Rumbling:  IF air pressure within the system is correct, the sound is due to movement within the sheet metal.  This is likely due to the thickness of the sheet metal used.
  • Booming: A loud booming sound is common where the ductwork connects to the furnace.  This area endures the greatest temperature swing, and there may be inadequate expansion joints to isolate the noise.

Ways To Minimize These Sounds:

  • If your ducts are pressing against wood, use rubber pads to separate the ductwork from the wood.
  • Insulating the ductwork will help minimize expansion & contraction, plus it reduces the amount of audible noise that occurs.
  • To minimize these noises more, changing the ductwork may be needed.  1. Change the ductwork shape.   2. Replace ductwork with thicker metal, or flexible ductwork.


Sounds From The Furnace

Now we are going to turn our attention to the HVAC equipment itself.  We will discuss noises that are normal and you should expect to hear.   We will also discuss noises that may be an indicator of a problem with your HVAC System.

Today’s gas, forced air furnaces come in various efficiency levels.  The different efficiencies also make different amounts of noise.   If your furnace is in the attic, furnace operating noise is less of an issue.  If your furnace is within the living space, a furnace can be a constant source of noise all winter long.

old gas furnace

Image Source: CanStockPhoto

SHOWN:  The Openings At The Front Of An 80% / Standard-Efficiency Furnace Are For It To Draw In Air For Gas Combustion.

These Holes Allow Noises Generated By The Furnace To Be Easily Heard

You Will Hear 3 Noises When A Standard-Efficiency Furnace Goes Through A Heating Cycle:

1. A small motor.  It draws air (from inside your home) into the combustion chamber.  Then this motor removes the exhaust gasses to outside the home.

2. The burners lighting.  This will sound somewhat like a quiet “swoosh”.

3. The blower fan motor.

With each step, the furnace makes more noise.  Once the furnace has reached the thermostat setting, it turns off the burners, a little later it turns off the Draft-Inducer Motor, a little later it turns  the blower motor off.


High-Efficiency Furnace

electric furnace

Image Source: CanStockPhoto

A 92%+ / High-Efficiency Furnace Has No Holes In The Front Panel.  It Draws Combustion Air From Outside Through A White Plastic Pipe.

With The Combustion Area Closed Off, Notably Less Noise Can Be Heard From The Furnace


Sounds From The Outside A/C Unit

The A/C outside unit makes a lot of noise while moving tremendous amounts of air, and creating a lot of air-volume noise.   The compressor in this unit makes noise too.   Also, IF you have a Heat Pump, the amount of noise generated during the defrosting cycle can be quite loud depending on its brand and model.

The location of the outdoor unit is a big factor too, as many are located near bedrooms.   This can cause problems while the outside unit cycles on & off all night long.  It is often too costly to relocate the outdoor unit.  And in many cases there are no superior locations.

Dirty & Clogged Outside A/C Compressors Make More Noise

If your outside A/C unit is dirty, it will make more noise.  This is because the air volume is being drawn through a smaller area than the unit is designed for (because some fins are clogged with dirt and debris).  This causes faster air speed through the coils where they are not clogged.  Faster moving air will always make more noise.

Dirt build-up on the fan blade will cause it to make more noise.  The thicker the dirt, the more surface area, and the more noise the dirty blade makes, and the built up dirt creates more air resistance.

A Loose Service Panel On Outdoor Unit Can Rattle Or Vibrate

Loose Panel: Sometimes the panels on the cabinets become dislodged because screws have worked loose, or weren’t screwed tightly after the panel was opened.  Before considering other issues, make sure the panels are secure.   To test this, simply push on the panel.  If the rattle stops, the screws holding the panel need to be tightened.

If You Are Replacing Your HVAC System 

If you are replacing your HVAC System, nearly all A/C brands use Copeland brand central air conditioner compressors.  Two top brands do not use Copeland.  American Standard & Trane A/C use their own proprietary ClimaTuff brand compressor.   ClimaTuff compressors operate more quietly.  This is especially the case with their Heat Pumps during defrosting.

The A/C compressor is the component responsible for moving the refrigerant throughout the outside unit & furnace cooling coil (this coil is inside the furnace or ductwork and can’t be seen without removing a panel).

  • American Standard & Trane have 2 Variable Speed A/C outdoor units rated at 55 decibels. The XV20i and the XV18. **
  • Rain noise level = 50db   *4
  • Normal conversation = 60db *4
  • Each +10db doubles the volume level to the human ear
  • At 55 decibels, the 2 A/C mentioned are under 1/2 as loud as a 70 decibel unit

Click Here To Hear A New Trane A/C, Compared To An Older A/C Of A Different Brand: Trane A/C Outside Unit Noise Level

  • Goodman SEER-18 (with Copeland Compressor) operates at 71–74 decibels.  ***
  • Vacuum Cleaner = 70db *4
  • Hair Dryer = 80db *4
  • Not all the noise is created by the compressor.  The fan and moving air make a lot of noise.  The db quoted are total operating noise.
  • Different fan blades create different amounts of noise.
  • The pitch (angle) of the fan blades factors into how much air the blade can move at the same ration speed.
  • NOTE:  You cannot replace a central A/C fan blade with something other than one identical to the original.
  • Doing so can cause it to overheat due to insufficient air passing through it.
  • A unit that overheats will increase cooling costs and reduce how long it lasts.

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If You Are Bothered By Noise From Your Current A/C, But Don’t Need A New One

There is a way to notably reduce the amount of noise than can be heard. sells noise-reducing panels specifically for HVAC.

Click Here To Hear A Demonstration Of QuietFence’s effectivness:  Hear QuietFence Effectiveness

This product could also be placed between the house and the A/C unit, to lower noise transfer inside the home at the location of the the outside A/C unit.

Note: This is not an endorsement for Quiet Fence, only because we don’t have first-hand knowledge of all noise-reducing fences.


If You Hear A New Noise Coming From Your Furnace

Click Here To Read: Gas Furnace Failure — What Goes Wrong & Why


If You Hear A New Noise Coming From Your A/C Unit

Click Here To Read: Common Central Air Conditioner Problems


If You Hear A New Noise Coming From Your Heat Pump

Click Here To Read: Common Heat Pump Problems



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 Wylie TX, Murphy, TX, and Rowlette, TX.  We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge. We service all homes in southern Collin County, TX & Denton County, TX with no additional travel charge.

Al’s also provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally, we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).