Set your thermostat to heat, and a fixed sequence begins inside the furnace cabinet. The thermostat closes a circuit and calls for heat.

A correctly matched cooling system runs 10 to 20 minutes once the compressor starts, and longer as the load rises.

You put a hand under the register in the back bedroom, and the air on your palm is thin.

A light-commercial rooftop unit does two jobs from one cabinet above your ceiling. During a cooling peak, its compressor, condenser fan, and supply blower run for long stretches against the heat your occupants and equipment add.

Your hallway thermostat reads 74, and the bedroom at the end of the hall reads 74 as well.

The wind dies down, the sky lightens, and you finally walk back inside after checking the yard for downed branches.

You open the closet door to grab something and step in a puddle you didn't leave there.

A furnace does not heat your home by mixing flame with the air you breathe.

The outdoor unit hums, hesitates, then finally kicks on with a shudder you can feel through the wall.

You walk in, bump the thermostat down, and for the first two or three minutes the air coming out of the vents smells like a basement that's been shut up for a season.

A ductless mini-split is a heat pump that has been split into parts and stripped of its ductwork.

A C-wire, short for "common wire," gives your thermostat a steady, always-on supply of 24-volt power.

Standing in the filter aisle with a wall of cardboard-framed rectangles in front of you, each one stamped with a different number, is a familiar kind of stuck.

Most home comfort equipment does one job. A furnace burns gas to make heat. An air conditioner runs a cooling cycle.

You stand under a supply register with your hand up, and you can hear the indoor unit running in the closet or attic, but almost nothing lands on your palm.

You set the thermostat to 72, the downstairs feels almost chilly, and yet the upstairs bedrooms sit warm and stuffy at bedtime.

Warm air from the vents on a day you need cooling is one of the most common calls an HVAC tech gets, and it almost always traces back to a single idea most homeowners have backward.

For a part the size of a soda can, the capacitor punches far above its weight.

The hail passes, and you walk out to find the outdoor half of your air conditioner looking like it went ten rounds, the casing dented and the delicate metal fins flattened and mashed on the side that faced the storm.

You framed the new bonus room, the primary suite, or the enclosed porch, and now it needs to stay comfortable in a part of the country where the cooling season runs long.