98 Fun Facts About HVAC

Willis Carrier was a research engineer at which firm when he designed the first modern air conditioner in 1902?

Buffalo Forge hired Carrier straight from Cornell in 1901; when it shut its air-conditioning arm in 1914, he and six colleagues left to found the company that still bears his name.

Which North Carolina textile-mill engineer coined the term 'air conditioning' in 1906?

Stuart W. Cramer coined 'air conditioning' in 1906 for his way of adding moisture to mill air, which made cotton yarn easier to spin and less likely to break; Willis Carrier's firm later took up the phrase.

Willis Carrier's first air-conditioning system, installed in 1902, controlled humidity for what kind of Brooklyn business?

A printing plant: at Sackett & Wilhelms, humid summer air made the paper wrinkle and swell between press runs so coloured inks no longer lined up, and Carrier's machine was built to steady the air for the presses.

Carrier's company moved to which place in upstate New York, where a university's domed stadium bore its name?

Syracuse let Carrier pull together factories scattered across four cities; decades later the firm's gift put its name on Syracuse University's stadium, the Carrier Dome.

Which machine did Willis Carrier unveil in May 1922, opening the door to cooling large buildings such as theatres?

The centrifugal chiller had fewer moving parts and compressor stages than the machines before it, so big cooling systems became cheaper and more reliable and comfort cooling spread quickly to large public buildings.

Where was the Rivoli Theatre, the grand cinema that Carrier air-conditioned in the 1920s?

New York City's Rivoli was a movie palace off Times Square; for many Americans in the 1920s, a cinema like it was the first place they ever felt mechanically cooled air.

Which automaker was the first to offer an air-conditioning unit in its cars, in 1939?

Packard's unit put its cooling coil and blower in the boot, taking up half the trunk, and the compressor ran whenever the engine did; with no clutch to disengage it, stopping the cold meant removing the drive belt.

In 1931 H.H. Schultz and J.Q. Sherman developed the most common type of which appliance, early models costing $10,000 to $50,000?

The room air conditioner sat on a window ledge; early units cost several times the price of a house at the time.

John Gorrie patented an ice-making machine in 1851 in the fever-prone Florida port of Apalachicola; what was his profession?

Physician John Gorrie built the machine to cool the rooms of his fever patients; he died financially ruined in 1855, yet Florida later chose his statue to represent the state in the US Capitol.

In which country did newspaperman James Harrison build an early refrigeration works in the 1850s, before trying to export frozen meat?

Australia's Geelong was where Harrison ran a newspaper; in 1873 he loaded the ship Norfolk with frozen beef and mutton for Britain, but the cargo spoiled on the voyage.

Frederick McKinley Jones, who invented refrigeration units for trucks, co-founded which company with Joseph Numero?

Thermo King began as the U.S. Thermo Control Company; Jones's units carried fresh food to troops in the Second World War and afterwards changed how groceries were shipped, letting perishables travel long distances by road.

In 1991 Frederick McKinley Jones posthumously became the first African American to receive which honour?

The National Medal of Technology was presented to Jones's widow by President George H.W. Bush, 30 years after the inventor's death; he shared the award with his business partner, Joseph Numero.

In an air conditioner, liquid refrigerant absorbs heat from indoor air as it passes through which component?

The evaporator coil runs cold enough for moisture in the air to condense on it, so an air conditioner also works as a dehumidifier.

Which refrigeration-cycle component is also known as the metering device?

The expansion valve (or a capillary tube) is the metering device; it creates the pressure drop that lets refrigerant flash into a cold, low-pressure mist just before it enters the indoor coil.

Freon was developed in the late 1920s as a safer refrigerant by researchers at which company, then the owner of Frigidaire?

General Motors set its researchers to find a non-toxic, non-flammable replacement for the ammonia and sulfur dioxide that made early fridges dangerous, then formed a joint company with DuPont in 1930 to produce it.

Which inventor helped create both leaded petrol and the first CFC refrigerants?

Thomas Midgley Jr. died in 1944; decades later both of his inventions were phased out worldwide for the harm they did to human health and the ozone layer.

Which agreement, signed in 1987, was among the first treaties ever ratified by every United Nations member state?

The Montreal Protocol phased out the CFCs once standard in fridges and air conditioners; a UN-backed assessment in 2023 found the ozone layer on track to recover within about four decades.

The 2016 Kigali Amendment phases down which class of refrigerants, adopted widely as replacements for ozone-damaging CFCs?

HFCs spare the ozone layer but are potent greenhouse gases, so the amendment turned an ozone treaty into a climate one: cutting them 80 to 85 percent by the late 2040s should avoid up to 0.5 °C of warming by 2100.

Which two chemists predicted in 1974 that CFCs would deplete the ozone layer?

Molina and Rowland published their warning in Nature in 1974 and met heavy criticism, but later measurements showed they had, if anything, underestimated the risk; they shared the 1995 Nobel Prize in Chemistry with Paul Crutzen.

When R-22 was restricted in the 2010s, most new US home ACs shifted to which refrigerant?

R-410A, sold as Puron, spared the ozone layer but proved a potent greenhouse gas, so US rules in turn barred it from new home systems from 2025.

Which hydrocarbon became the main refrigerant in European household refrigerators after Greenpeace championed it in the 1990s?

Isobutane, coded R-600a, was part of the hydrocarbon coolant in the Greenfreeze fridge that Greenpeace launched in 1993 with an East German manufacturer, built to show that refrigerators did not need fluorocarbons at all.

A 'ton' of cooling capacity is defined as how many BTU per hour?

One ton of cooling is 12,000 BTU per hour, roughly what a 500-square-foot room needs; going bigger backfires, because an oversized unit cools the air before it has had time to remove the humidity, leaving the room clammy.

The 'ton' used to rate air conditioners originally compared a machine's cooling over a day with a ton of what?

Ice was what people cooled with before machines, so early refrigeration machines were rated by how many tons of melting ice a day they could match, and the unit stuck.

A British thermal unit is the heat needed to raise how much water by one degree Fahrenheit?

One pound of water warmed by one degree Fahrenheit defines the BTU, roughly the heat of one burning kitchen match; a single unit is so small that US natural gas is priced by the million.

In 2006 US rules raised the lowest rating for new central air conditioners from 10 to 13 on which scale?

SEER, the seasonal energy efficiency ratio, divides a summer's cooling output by the electricity used; moving from 10 to 13 cut the power needed for the same cooling by nearly a quarter.

In the furnace efficiency rating AFUE, what does the letter A stand for?

Annual, because AFUE (Annual Fuel Utilization Efficiency) averages a furnace over a whole heating season, start-ups and cool-downs included, rather than quoting its best steady-state figure.

High-efficiency condensing furnaces are vented with PVC pipe rather than metal to prevent what?

The acidic condensate would corrode metal flue pipe; a condensing furnace's secondary heat exchanger pulls so much heat from the exhaust that water vapour condenses out, so plastic venting prevents corrosion.

Which component makes a heat pump different from an air conditioner, letting it both heat and cool a home?

The reversing valve flips the direction the refrigerant flows, so the outdoor coil that dumps heat in summer gathers it in winter and one machine does both jobs.

Which London venue opened in 1951 with a reversible water-source heat pump fed by the River Thames?

The Royal Festival Hall's heat pump was driven by two Rolls-Royce Merlin aircraft engines converted to burn town gas; it worked, but it was taken out once the Festival of Britain was over.

A pioneering 1948 heat pump drawing warmth from groundwater was installed in the Commonwealth Building in which Pacific Northwest city?

Portland, Oregon's Commonwealth Building was a sealed tower with no opening windows, so even in a mild climate it needed air conditioning, and its heat pumps supplied both the heating and the cooling.

Warren Johnson, a teacher who patented an electric thermostat in 1883, founded the forerunner of Johnson Controls in which state?

Wisconsin: Johnson built the device for his college at Whitewater, where it rang a bell telling the boiler man to adjust the damper, then took it to Milwaukee to find a backer and started his company there in 1885.

Which industrial designer styled Honeywell's round T87 thermostat, first made in 1953?

Henry Dreyfuss, who also styled Bell telephones, gave the T87 its round form; the concept came from Honeywell engineer Carl Kronmiller, and the circle hid the crooked look of rectangular thermostats hung on walls.

Nest Labs founders Tony Fadell and Matt Rogers were both former engineers at which company?

Apple was where Fadell had led the creation of the iPod and where he met Rogers; they started Nest in 2010, and Google bought it in January 2014 for $3.2 billion.

A Roman hypocaust heated a room mainly by circulating hot furnace air where?

Under a floor raised on pillars, hot air from a wood fire spread beneath the room; it burned so much fuel and needed such constant tending that hypocausts were mostly found in public baths and wealthy villas.

Which Founding Father invented a fireplace stove in the 1740s and refused to patent it?

Benjamin Franklin wrote that since we enjoy great advantages from the inventions of others, we should gladly share our own; by his account a London ironmonger then patented a slightly altered version and made a small fortune from it.

Saint Petersburg's Franz San Galli developed which heating device, his 'hot box', in the 1850s?

The radiator made San Galli's name, though others had built similar heaters earlier and his claim to be its inventor is disputed; his workshop of 12 men grew into a factory making heating, water-supply and sewerage equipment.

What does the air-filter rating MERV stand for?

Minimum Efficiency Reporting Value means a filter is rated by its worst-case capture of particles from 0.3 to 10 micrometres; higher is not always better, because a denser filter can choke the airflow of a system not built for it.

Which filter type must trap at least 99.97% of particles 0.3 micrometres across?

HEPA filters are tested at 0.3 micrometres because that is about the hardest size to catch: larger and smaller particles are generally trapped even more efficiently, so 99.97 percent is the filter near its worst.

Which society, founded in New York in 1894, writes ventilation and energy standards cited in US building codes?

ASHRAE began as a society of heating and ventilating engineers and gained the R in its name by merging with the refrigerating engineers' society in 1959.

A 1976 outbreak traced to a Philadelphia hotel's air-conditioning system gave which disease its name?

Legionnaires' disease is named for the American Legion members who fell ill after a convention at the Bellevue-Stratford Hotel, which closed within months; the bacterium itself was not identified until January 1977.

Engineers Frederik van Iterson and Gerard Kuypers, who patented the hyperboloid cooling tower, came from which country?

The Netherlands' state coal mines built the first such towers at the Emma mine near Heerlen by 1918; the waisted shell needs less material than a straight cylinder giving the same draught, and stands up better to wind.

Evaporative 'swamp' coolers are most effective in which kind of climate?

Hot and dry air gives the biggest effect: cooling comes from water absorbing heat as it evaporates, so the drier the air, the larger the temperature drop, at the cost of adding humidity.

The slim wall-mounted 'mini-split' air conditioner was developed in the 1960s in which country?

Japan's Toshiba sold a split air conditioner for homes in 1961, billed as the world's first, and in 1968 Mitsubishi Electric's slim cross-flow fan made the indoor unit thin enough to hang on a wall.

Which company invented variable refrigerant flow (VRF) technology in 1982?

Daikin Industries created VRF; heat-recovery versions can warm some rooms with the heat pulled out of others at the same time.

Which state barred cloth duct tape on ducts after a 1998 study at a national laboratory there found it failed?

California acted on tests at Lawrence Berkeley lab, where Max Sherman's team heat-cycled every duct sealant it could find and reported that only duct tape failed, 'reliably and often quite catastrophically'.

What is the term for the temperature at which water vapour in the air begins to condense into liquid?

Dew point is why cold drinks, windows and uninsulated ducts 'sweat' in summer: any surface cooler than it pulls water out of the air, the same effect an air conditioner's cold coil uses to wring moisture from a room.

Under EPA Section 608, a Type I technician certification covers servicing which equipment?

Small appliances such as fridges and window units need only Type I; the card never expires, and it matters at the supply counter, because refrigerant may be sold only to technicians certified for that kind of equipment.

Roughly what share of global electricity did air conditioning consume in 2022?

About 7 percent, on International Energy Agency figures; the agency expects the number of air conditioners to nearly triple by 2050, driven less by hotter weather than by rising incomes in hot countries such as India and Indonesia.

Airtemp, a climate-control brand, made its first installation in 1930 in which New York skyscraper?

Airtemp was Chrysler's own climate-control brand, so its first job was the Chrysler Building itself; the carmaker later fitted Airtemp units to its cars and sold the business to Fedders in 1976.

Most modern home thermostats run on low-voltage control circuits of roughly how many volts AC?

Thermostats run on a 24-volt circuit fed by a transformer on the furnace or air handler; mechanical types use a bimetallic strip, and some add an 'anticipator' that cuts the burner just before the setpoint.

Robert C. Webber built the first ground-source heat pump in the 1940s after experimenting with which appliance?

Webber noticed his deep freezer's outlet pipe ran hot, captured that heat first for water and then for his house, and ended up with copper coils buried in the ground in place of the freezer.

What is the term for warm air escaping through a building's high openings while pulling cooler air in through low ones?

The stack effect grows with a building's height and the gap between indoor and outdoor temperatures; it is the same buoyancy that makes a chimney draw, which is why a taller chimney pulls harder.

A room is under positive pressure when what is true of its airflow?

More air is supplied than exhausted, so any leak flows outward and unfiltered air cannot seep in, which is why chip-making cleanrooms run this way; isolation rooms for infectious patients do the reverse.

What is the term for heating systems that use water as the heat-transfer medium?

Hydronics covers systems that move heat in water or steam; most hot-water versions use a circulator pump to push the water round the loop, whereas steam travels through the pipes under its own pressure.

Which instrument does an HVAC technician use to read gas pressure and duct static pressure in inches of water column?

Manometer readings are still given in inches of water because the original instrument was simply a tube of liquid, with the pressure shown by how far it pushed the column up.

Which US agency advised in 2023 that buildings aim for at least five air changes per hour of clean air?

The CDC is a disease-control agency, not a building regulator: its 2023 advice on cutting airborne germs counts filtered air as well as fresh air, so a room can reach the target with a portable air cleaner.

Alfred Wolff designed one of the first comfort air-conditioning systems for which financial landmark?

The New York Stock Exchange moved into its new building in 1903 with Wolff's system in place; unlike the factory systems of the day, it was meant to keep people comfortable rather than to protect a product.

The first home air conditioning was installed in 1914 in the Charles Gates mansion in which city in Minnesota?

Minneapolis millionaire Charles Gates ordered a cooling unit some seven feet high and twenty feet long for his new mansion, but he died in 1913 and nobody ever lived in the house, so the machine may never have been switched on.

The HEPA air filter in today's home purifiers was designed in the 1940s for use on which secret wartime programme?

The Manhattan Project needed the filters to stop airborne radioactive contamination spreading, and the design was only commercialised in the 1950s.

Philip Diehl built the first electric ceiling fan in 1882 by adapting a motor he had designed for which device?

A sewing machine motor was the starting point: Diehl had engineered it for Singer, then mounted fan blades on it and fixed it to the ceiling.

Natural gas has no smell of its own, so utilities add sulfur compounds that make a leak smell like what?

Rotten eggs is the smell of the mercaptans added to household gas, a precaution US lawmakers pushed for after an undetected leak destroyed a Texas school in 1937.

Which colourless, odourless gas from a faulty furnace or blocked chimney is why homes need a dedicated alarm?

Carbon monoxide forms when fuel burns incompletely, and it binds to haemoglobin so the blood can no longer carry oxygen round the body.

Many older dial thermostats switched a furnace on by tilting a small glass vial holding a bead of which element?

Mercury is a toxic heavy metal, so an old thermostat with one of these tilt switches has to be handled as hazardous waste.

Tax-exempt home heating oil in the United States is dyed which colour so inspectors can spot it in road vehicles?

Red dye marks the fuel as untaxed, and the rules call for five times the usual concentration so it still shows when mixed with legal road diesel.

The ondol, which warms a house with smoke channelled from a cooking fire, is traditional to which country?

Korea's ondol draws the smoke through stone passages to a chimney on the far wall, and the word is now also used for Korean-style hotel rooms.

Which cartoon character has been the mascot of Owens Corning's fibreglass home insulation since 1980?

The Pink Panther fits because the insulation itself is dyed pink, a colour the company went on to register as a trademark.

Which capital city heats its homes with geothermal hot water, then pipes it under streets to melt snow and ice?

Reykjavík sends the water under streets and sidewalks at about 30 °C, and Iceland moved its district heating off oil after the price shocks of the 1970s.

Which British company announced the Air Multiplier, a fan with no exposed spinning blades, in 2009?

Dyson was not first to the idea: Toshiba patented a bladeless fan design in 1981 but never marketed it before the patent expired.

To bring warm air down in winter, official US advice is to run a ceiling fan in which way?

Clockwise, low speed circulates the warm air pooled at the ceiling back into the living space; in summer the direction is flipped to make a cooling breeze.

Which gas that builds up inside houses does the EPA call the top cause of lung cancer in non-smokers?

Radon is usually kept out with a vent pipe and fan that pull the gas from beneath the house and release it outdoors.

Which fire-resistant mineral, widely used as pipe and ceiling insulation, was later tied to mesothelioma?

Asbestos went into roofing, drywall and even lawn furniture before its health effects were widely acknowledged in the 1970s.

Which US government label for efficient furnaces and air conditioners began in 1992 as a scheme for computers?

Energy Star was set up by the Environmental Protection Agency, and its first labels went on computers and their peripherals before spreading to heating and cooling equipment.

Warm air rising from a baseboard heater and circulating round a room shows which mode of heat transfer?

Convection moves heat in a flowing fluid, and when buoyancy alone drives the flow, as above a heater, engineers call it natural; add a fan and it becomes forced.

Which condition, often blamed on poor ventilation, brings symptoms that ease soon after workers leave?

Sick building syndrome was linked to fuel-saving standards that cut the outdoor air required per person after the 1973 oil crisis.

The natural gas burned in most home furnaces and water heaters consists chiefly of which hydrocarbon?

Methane makes up about 95% of typical pipeline gas, with small amounts of heavier alkanes and traces of nitrogen and helium.

On a roll of loft insulation, which rating shows how well it slows heat flow, with higher numbers insulating better?

R-value is the reciprocal of the U-factor quoted for windows, so the two run in opposite directions: good insulation scores high on one and low on the other.

Which instrument measures the humidity of air, one 1783 version using a stretched human hair as its sensor?

The hygrometer with a hair sensor was the work of Swiss physicist Horace Bénédict de Saussure, three centuries after Leonardo da Vinci devised a prototype.

In a home air conditioner, which component pumps refrigerant gas around the sealed loop, warming it as it goes?

The compressor leaves the refrigerant hotter than the air outside, which is what lets a cooling system shed a house's warmth outdoors even in midsummer.

In a house heated by radiators, which appliance does the job a furnace does in a forced-air system?

A boiler does not have to live up to its name: in hot-water systems the water sent to the radiators is heated without ever boiling.

In a gas furnace with a pilot flame, which sensor generates the trickle of electricity that holds the gas valve open?

A thermocouple sitting in the flame works as a fail-safe: if the flame goes out it stops producing power, and the gas supply shuts off by itself.

Which term did chemist Joseph Black introduce for energy that changes a substance's state but not its temperature?

Latent heat takes its name from the Latin for lying hidden: melting ice soaks it up while the thermometer refuses to move.

In a gas furnace, which component passes the burners' warmth to household air while keeping combustion fumes out?

A heat exchanger can fail from metal fatigue after years of warming up and cooling down, and it is the barrier between burner fumes and the air a family breathes.

In a forced-air system, which box-like chamber links the furnace to its branch ducts?

Plenum also names the airspace above a dropped ceiling, where cabling has to be a special fire-resistant grade because air circulates through it.

Which plate or valve inside a duct or chimney opens and closes to regulate the flow of air?

A damper in a fireplace chimney keeps weather and birds out when shut, and motorised versions let a single furnace heat separate zones.

What is the name for the passage inside a chimney that carries a furnace's combustion gases outdoors?

Flue once meant the whole chimney, and US codes forbid using ordinary ductwork as one because combustion gases need their own continuous route outdoors.

Which home-audit test uses a powerful fan to change a whole house's air pressure and measure how leaky it is?

The blower door began life in a window: Swedish testers first mounted the fan there in 1977, and a Princeton team later moved it to the doorway.

Which efficiency figure for a heat pump divides the heating delivered by the work put in, and usually exceeds 1?

COP stands for coefficient of performance, and it can pass 1 because a heat pump moves existing warmth instead of making it, something no ordinary electric heater can do.

Which measure of combined heat and humidity is thought fatal to healthy people if sustained above 35 °C?

Wet-bulb temperature is read from a thermometer in a water-soaked sock, and above that threshold the body starts gaining heat from its surroundings, even in shade beside a fan.

On a psychrometric chart, which property expresses the total heat content of moist air, water vapour included?

Enthalpy adds the heat carried by water vapour to that of the air itself, so controls that bring in outside air for cooling check it, not just the thermometer.

Which HVAC feature cools a building with cool outside air instead of mechanical refrigeration?

An economizer provides what engineers call free cooling: when outside air is cool and dry enough, it needs no further conditioning at all.

Which open networking standard, adopted by ASHRAE in 1995, lets building controls from rival makers communicate?

BACnet is short for building automation and control networks, and work on it began at a committee meeting in Nashville in 1987.

The dark, sun-facing masonry wall behind glass that warms a building with stored sunshine honours which Frenchman?

Félix Trombe gave the wall his name through his extensive work on solar buildings, though Edward S. Morse had patented a similar glazed air heater back in 1881.

Which unit, counted against a 65 °F baseline in the US, measures how much heating a spell of weather demands?

A degree day is clocked up when the outside temperature sits one degree below the baseline for a full day, the baseline being the point above which a building needs no heating.

Fans and ventilation rates are specified in CFM, a measure of delivered airflow that stands for what?

Cubic feet per minute is the unit ventilation standards are written in: ASHRAE's rules set a required amount of outdoor air for every occupant.

Which ultra-efficient building standard was first met by four terraced homes in Darmstadt in the early 1990s?

Passive house buildings are so airtight and well insulated that conventional heating systems can be downsized or left out altogether.

Which law of thermodynamics explains why moving heat from a cool room to hot outdoors takes power?

The Second law, in Rudolf Clausius's 1850s wording, says heat can never pass from a colder body to a warmer one without some other change taking place.

Which tarry residue, left inside chimneys by cooling wood smoke, is the usual fuel of a chimney fire?

Creosote forms when wood burns with too little airflow, and the chimney fires it feeds are counted as the substance's deadliest effect.

What do HVAC engineers call outside air entering a building unintentionally through cracks in its envelope?

Infiltration is driven by wind and by warm air's buoyancy, and engineers rate it in air changes per hour: how often the leaks replace a building's whole volume of air.