How Willis Carrier Invented the Modern Air Conditioner
Willis Carrier's 1906 patent for an apparatus to control humidity and temperature, forming the technical foundation for modern air conditioning systems.
Original patent title: “Apparatus for treating air.”
Willis Carrier's 1906 patent for an apparatus to control humidity and temperature, forming the technical foundation for modern air conditioning systems. Granted to Buffalo Forge Co in 1906 with 19 forward citations, and it is now in the public domain.
Key facts
Coverage
What does this patent actually cover?
The apparatus treats air by passing it through a spray of water to control its moisture content and temperature. By adjusting the temperature of the water spray, the system can either cool the air or remove humidity through condensation. This process allows for the precise regulation of the air's dew point, which is the temperature at which water vapor turns into liquid. The device essentially creates a controlled environment by balancing thermal and moisture levels within a stream of air.
The gap
What does this patent NOT cover?
- Does not cover chemical-based air purification or filtration systems.
- Does not cover modern vapor-compression refrigeration cycles using chemical refrigerants.
- Does not cover systems that lack a water-spray-based humidity control mechanism.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
Carrier realized that by controlling the temperature of the water spray, he could precisely dictate the moisture content of the air, effectively decoupling temperature control from humidity control.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Industrial textile mill climate control
Early 20th-century printing press humidity regulation
Commercial HVAC systems
Why it matters
The bigger picture
This patent marks the birth of modern climate control. It enabled industries like printing and textiles to operate regardless of weather conditions, and eventually transformed global architecture and human comfort by making indoor environments habitable in extreme heat.
Filed
September 16, 1904
Granted
January 2, 1906
Market context
Who's building on this
Companies in this space
The Carrier Corporation remains a global leader in HVAC technology, continuing to refine the principles of thermal management established by this patent. Major competitors like Trane and Daikin also operate within the technical lineage of this foundational work.
Market impact
This patent enabled the creation of the multi-billion dollar HVAC industry. It allowed for the expansion of manufacturing into hot climates and fundamentally changed urban development by permitting the construction of skyscrapers that could be kept cool and dry.
Claim 1 — Plain English
What this patent covers
The apparatus treats air by passing it through a spray of water to control its moisture content and temperature. By adjusting the temperature of the water spray, the system can either cool the air or remove humidity through condensation. This process allows for the precise regulation of the air's dew point, which is the temperature at which water vapor turns into liquid. The device essentially creates a controlled environment by balancing thermal and moisture levels within a stream of air.
The clever bit
Carrier realized that by controlling the temperature of the water spray, he could precisely dictate the moisture content of the air, effectively decoupling temperature control from humidity control.
What it does not cover
- Does not cover chemical-based air purification or filtration systems.
- Does not cover modern vapor-compression refrigeration cycles using chemical refrigerants.
- Does not cover systems that lack a water-spray-based humidity control mechanism.
Patent Journey
From filing to expiry
PatentBrief Score
Impact Score
Moderate
Citation count
26/40
Moderately cited
Claim breadth
0/20
Narrow claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more →
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$14K – $46K
Midpoint $29K · expired or expiring · industry ×1.6
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Concepts involved
Citations
Patent lineage
Cite this patent
Carrier, W. H. (1906). How Willis Carrier Invented the Modern Air Conditioner (U.S. Patent No. 808,897). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/808897/air-conditioning-carrier
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
Embed
Add this patent to your site
Drop this plain-English patent card into any blog post or article — free, no signup. It always links back to the full breakdown here.
<div data-patentlens-widget data-patent-number="US808897"></div> <script src="https://patentbrief.org/embed.js" async></script>
Stay in the loop
Get a weekly digest of new patents.
One email per week. No spam. Unsubscribe anytime.
Keep exploring
Related patents you should know
US 4683195 · 1987
How to Make Billions of Copies of a DNA Segment
This patent describes the Polymerase Chain Reaction (PCR), a method to rapidly create many copies of a specific piece of DNA or RNA, enabling its detection and analysis.
Cetus Corp
US 8697359 · 2014
How to Edit Genes in Human Cells Using an Engineered CRISPR System
This patent describes an engineered CRISPR-Cas9 system for precisely cutting DNA in eukaryotic cells to change how genes work, opening the door for gene editing in complex organisms.
Massachusetts Institute of Technology
US 7657849 · 2010
How the iPhone's Slide-to-Unlock Gesture Works
Apple's 2010 patent describes unlocking a device by dragging a specific graphical image across the touchscreen along a predefined path, a gesture that became iconic with the original iPhone.
Apple Inc
US 4733665 · 1988
How Doctors Implant a Permanent Stent Using a Balloon
This patent describes the method for placing a permanent, expandable wire mesh tube inside a blood vessel or other body tube using a balloon-tipped catheter to widen it and keep it open.
Expandable Grafts Partnership
US 4405829 · 1983
How RSA Public-Key Encryption Keeps Digital Messages Secret
This patent describes the foundational RSA algorithm, a method for securely sending messages where anyone can encrypt a message using a public key, but only the intended recipient can decrypt it using a secret private key.
Massachusetts Institute of Technology
US 4575330 · 1986
How 3D Printers Build Objects Layer by Layer from Liquid
This patent describes the foundational method for 3D printing, where a machine builds a three-dimensional object layer by layer by hardening a liquid material with light or other energy.
UVP Inc
Semantically similar
You might also find these interesting
US 8080 · 1851 · John Gorrie
John Gorrie's 1851 Patent for Artificial Ice Production
US 2495429 · 1950 · Raytheon Manufacturing Co
How Percy Spencer Invented the Microwave Oven
US 2133235 · 1938 · Owens Illinois Glass Co
How Glass Fibers Are Spun for Insulation
US 1203495 · 1916 · General Electric Co
How William Coolidge Invented the Modern X-Ray Tube
More to explore
More in Energy & Clean Tech
US 2708656 · 1955
How the First Nuclear Reactor Works
US 2780765 · 1957 · Bell Telephone Laboratories Inc
How the First Practical Silicon Solar Cell Works
US 223898 · 1880
How Thomas Edison Invented the Practical Incandescent Light Bulb
US 2742437 · 1956 · Oxy Catalyst Inc
How Eugene Houdry Invented the Modern Catalytic Converter
New to patents?
Common Questions
Frequently Asked Questions
What does How Willis Carrier Invented the Modern Air Conditioner cover?
Willis Carrier's 1906 patent for an apparatus to control humidity and temperature, forming the technical foundation for modern air conditioning systems.
Who owns patent US 808897?
Buffalo Forge Co owns this patent, granted in 1906.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 808897 cited by?
This patent has been cited by 19 later patents that build on its ideas.
What problem does this patent solve?
This patent marks the birth of modern climate control. It enabled industries like printing and textiles to operate regardless of weather conditions, and eventually transformed global architecture and human comfort by making indoor environments habitable in extreme heat.
What does this patent NOT cover?
Does not cover chemical-based air purification or filtration systems.
Patent monitoring