Cejas Cooling & Construction

Explore Heat, Temperature, and Pressure

Let’s step away from the blinking thermostats and humming vents for a second. This is about the quiet war behind your drywall. The physics of pressure, the language of temperature, the heat that moves like a thief in the night. Welcome to the space between comfort and collapse. This is where the system breathes—or chokes.

Temperature: The Fever of Matter

Temperature isn’t just a number. It’s molecular anarchy or discipline, depending on the setting. The faster those molecules dance, the hotter it gets. The slower they creep, the colder the world becomes. And at absolute zero—that cold, godless void at -459.67°F (0 Kelvin)—everything stops. No motion. No energy. Just silence so pure it would crack the sky.

Fahrenheit vs Celsius: Two Thermometers, Same Fire

• Fahrenheit is jagged and granular, American and unapologetic.
• Celsius is clean, rational, used by scientists and the rest of the world. Both measure the same thing: how fast atoms are punching the air. In the end, it’s just a dialect of thermodynamics.

BTUs: Calories for Buildings

The British Thermal Unit is a working-class hero of heat. One BTU raises a pound of water by one degree Fahrenheit. Your AC is doing tens of thousands of these every hour, lifting heat from your home like Sisyphus with a dolly.

Heat Always Moves

Heat never rests. It always moves from hot to cold, looking for equilibrium like a dog finding shade.

1. Conduction: Heat passed hand to hand, molecule to molecule. Like your skillet handle burning your palm.
2. Convection: Heat hitching a ride on air or water. Rising, swirling, shifting. That hot pocket of air in your attic? That’s convection.
3. Radiation: Heat moving with no medium at all. Sunlight on your face. Fire without touch. The oldest form of heat there is.

The Three Faces of Heat

• Sensible Heat: You can feel it. It raises temperature. Straightforward.
• Latent Heat: The ninja of thermodynamics. It changes state—water to steam, ice to water—without changing temperature.
• Specific Heat: A material’s stubbornness to heating up. Water needs a lot. Metal, not so much.

Pressure: The Weight of Air

You are standing beneath an ocean of sky. That sky has weight. At sea level, it presses down with 14.7 pounds per square inch (PSIA). Every HVAC system you work on is a conversation with that pressure.

Elevation: Where the Air Gets Thin

Climb a mountain and you’ll find the pressure dropping. That means water boils at a lower temp. That means refrigerants behave differently. That means your system, if not tuned for altitude, will perform like a hangover in thin air.

The Barometer: The Weatherman’s Compass

A barometer is a tool that reads the mood of the atmosphere. Traditional ones use mercury. The higher the pressure, the taller the mercury rises. At sea level, we expect 29.92 inches of mercury (in. Hg). Anything less and the weather’s about to turn.

The Language of Pressure

• Inches of Mercury (in. Hg): Used for measuring vacuum. A slow inhale.
• PSIA: Absolute pressure. Includes the weight of the atmosphere.
• PSIG: Gauge pressure. What your gauges read. It ignores atmospheric pressure.

At sea level:
0 PSIG = 14.7 PSIA
0 PSIA = -14.7 PSIG

How to Convert:

• PSIA = PSIG + 14.7
• PSIG = PSIA − 14.7
• 1 in. Hg = ~0.49 PSI
• 29.92 in. Hg = 14.7 PSIA

Why It All Matters

This is the code beneath the comfort. The reason the air feels light or heavy, the reason your system hums or groans. Heat, pressure, and temperature are not just numbers. They’re the language of entropy. Every system you touch is waging a battle against the laws of physics—and losing, slowly.

But for a while, with the right charge and the right pressures, you hold the line. You keep homes human. You bend the invisible just enough to let comfort exist.

This is the work. This is why you’re here. Between heat and heaven.