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How Quiet Are Through-the-Wall ACs Really? Tony’s Decibel Tests & Noise-Reduction Fixes

Most homeowners think noise is just part of owning a through-the-wall AC — that constant hum, the vibration, the whooshing airflow, the late-night rattle that wakes you up. They assume it’s normal.

Tony knows better.

A properly installed through-the-wall AC can be surprisingly quiet, quieter than many window units, and in some cases, even quieter than older ducted systems. But when they’re installed wrong? You’ll hear every vibration, every compressor pulse, every airflow choke, every sleeve rattle.

This blog breaks down real decibel numbers, how wall construction affects noise, brand behavior, and Tony’s personal list of noise fixes that actually work.

Let’s make your wall unit whisper.

1. What “Normal” Noise Sounds Like — Tony’s Decibel Benchmarks

Tony carries a decibel meter in his tool bag because noise complaints are one of the top reasons homeowners call him back after installation.

Here are his real-world readings:

Outdoor Sound (Measured 3 feet away):

Cooling-only units: 67–74 dB
Heat pump wall units: 66–72 dB
Electric heat mode: near silent (no compressor)

Indoor Sound (Measured at the unit):

Low fan: 46–54 dB
Medium fan: 50–58 dB
High fan: 56–64 dB

What do these numbers compare to?

45 dB = quiet home
55 dB = office noise
65 dB = restaurant conversation
75 dB = traffic passing by

A good wall AC should blend into background noise on medium fan and be barely noticeable on low fan.

If yours sounds like a lawn mower? Something’s wrong.

(Reference: Mechanical Noise Prevention and System Balancing Principles)

2. The Biggest Noise Source Isn’t the Unit — It’s the Sleeve

Most homeowners blame the machine, but Tony knows:

The sleeve is the source of 50% of all noise problems.

Common sleeve noise issues include:

sleeve not level
sleeve vibrating against framing
poor insulation
metal-on-wood contact
gaps causing whistling
sleeve depth too long
moisture causing pops and crackles

The sleeve is a metal box, and if it’s not isolated or insulated, it acts like a speaker amplifying noise.

Tony always checks sleeve condition before touching the unit.

(Reference: Air Distribution and Duct Sizing Reference)

3. Wall Construction Affects Noise More Than the AC Brand

Your wall is half the noise equation.

Brick / Masonry Walls

✔ quietest
✔ best for sound reduction
✔ ideal for heat pump units

Stucco Walls

✔ good sound performance
✘ can transmit vibration if not padded

Vinyl Siding + Wood Studs

✘ most noise transfer
✘ can rattle
✘ needs sleeve insulation

Drywall + Thin Exterior Walls

✘ loudest
✘ poor sound blocking
✘ often need extra foam insulation

The thinner the wall, the more sound gets indoors.

(Reference: Home Insulation and Envelope Performance Manual)

4. Brand Noise Behavior — What Tony Sees in the Field

Every through-the-wall AC brand has its sound profile.

Friedrich (Kühl & Uni-Fit)

quietest overall
best vibration control
studio-apartment friendly

GE & LG

moderate noise
great value
improved compressors in 2024–2025 models

Amana & older brands

noisier due to older compressor designs

Cheapest off-brand units

loudest
terrible vibration isolation
poor airflow tuning

But Tony reminds homeowners:

“A loud unit from a good brand = bad install.
A quiet unit from a bad brand = rare miracle.”

Installation is everything.

5. Fan Noise vs. Compressor Noise — Know the Difference

Fan Noise:

whooshing
rattling panel
uneven airflow
higher at medium/high speeds

This is airflow-related.

Compressor Noise:

humming
low rumble
pulsing
vibrating

This is mechanical.

Sleeve Noise:

rattling metal
buzzing
shaking
whistling

This is what Tony fixes the most.

(Reference: HVAC Noise and Acoustics Guidelines)

6. Heat Pump Noise — The Swoosh, The Pause, The “What Was That?”

Heat pump through-the-wall units have defrost cycles, which can confuse homeowners.

During defrost, you may hear:

swooshing
hissing
compressor slowing
unit pausing
steam outside

This is normal.
Tony teaches homeowners this so they don’t panic.

7. The Top 10 Noise Problems Tony Fixes Every Summer

1. Sleeve touching framing

→ Add foam isolation.

2. Sleeve tilted wrong direction

→ Water buildup → crackling noises.

3. Deep sleeve choking airflow

→ Compressor works harder → louder.

4. Poor sealing

→ whistling and air whooshing.

5. Loose mounting screws

→ constant rattling.

6. Dirty coils

→ higher pressure → louder operation.

7. Fan blade imbalance

→ vibration.

8. Filter installed backward

→ loud airflow turbulence.

9. Unit not centered in sleeve

→ cabinet rubs, causes buzzing.

10. Overcooling small rooms

→ short cycling → repeated compressor noise.

Tony fixes these in under 30 minutes on most service calls.

8. Tony’s Noise Reduction Fixes That Actually Work

Here’s what Tony does on real job sites to quiet wall units.

A. Add foam isolation to sleeve edges

This stops metal-on-wood vibration instantly.

B. Insulate sleeve interior

Foam board or acoustic insulation cuts noise by 20–40%.

C. Adjust sleeve depth

A unit that’s too far back recirculates air and gets loud.

D. Add a rubber isolation pad or bracket

Reduces vibration dramatically.

E. Level the sleeve correctly

Incorrect slope makes water pop, crackle, and hiss.

F. Seal gaps with HVAC-grade foam

Stops whistle noise.

G. Clean the blower wheel & coils

Dust = louder airflow + higher pressure.

H. Replace worn fan motors

Older motors get loud before they fail.

I. Tighten all cabinet screws

Many “mystery rattles” are loose panels.

J. Lower fan speed

If static pressure is too high, slowing the fan makes the unit quieter.

Tony never leaves a job without applying at least 3–4 of these fixes.

9. Room Setup Makes a Big Difference — Even Without Touching the AC

You can reduce noise by changing the room environment:

✔ Add carpet or rugs
✔ Hang curtains
✔ Use upholstered furniture
✔ Don’t block the airflow
✔ Avoid placing the bed right next to the unit
✔ Add wall sound panels (if needed)

Sound-absorbing materials reduce perceived noise dramatically.