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.
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.
Key facts
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 timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
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.
Claim text not yet imported for this patent
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.
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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