Glossary · Heating, cooling & ventilation

Short cycling

Also called: short cycles

When heating or cooling equipment turns on and off frequently in short bursts instead of running in steady, longer cycles.

What it means

It's often caused by oversizing: the system reaches the thermostat setting quickly and shuts off. Each start-up wastes energy and wears parts, and comfort suffers. Multi-stage or variable-speed equipment reduces it.

Why it matters in an audit

Short cycling is a sign the system may be oversized for the house, which is worth checking before replacing equipment after envelope upgrades shrink the load.

In Canada

NRCan suggests replacing a short-cycling furnace with a high-efficiency two-stage, three-stage or fully modulating model.

Sources

Learn more here

Sizing heating and cooling: the load calculation →

Related terms

Oversizing Installing heating or cooling equipment with much more capacity than the house needs, usually from rules of thumb, not a load calculation.
Variable-speed (inverter) compressor A compressor that ramps its speed up and down to match the heating or cooling needed, instead of switching fully on and off.
Load calculation An engineering calculation of how much heating and cooling a house needs, room by room, used to size equipment correctly.
Heat-loss calculation (CSA F280) A calculation of how fast a home loses heat on the coldest days it's designed for, used to size heating equipment; in Canada it follows CSA F280.
Single-stage, two-stage and variable-speed How many output levels heating or cooling equipment has: single-stage runs fully on or off, two-stage adds a low setting, and variable-speed adjusts smoothly.

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