When you’re purchasing a new HVAC system for your home, you may be tempted to buy the largest residential unit available. After all, it would seem like a larger unit would be better because it could heat or cool your home as rapidly as possible. However, this is one of those situations where what seems like “common sense” doesn’t actually make sense at all.
The essential problem with an oversized HVAC unit is that it will, in fact, heat or cool your home very quickly—too quickly! This leads to what we call short-cycling. That’s when your HVAC cuts on, runs for a short time (less than ten minutes), and then cuts off again. Short-cycling is bad for your energy bills, your comfort, and the lifespan of your HVAC unit.
It’s bad for your energy bills because your HVAC unit uses a large amount of energy every time it switches on, so a unit that’s frequently switching on and off and on again rather than running continuously will waste electricity, sort of like if you turned your car off and back on again at every stoplight.
Furthermore, it’s bad for your energy bills because your HVAC unit runs least efficiently when it first starts up. For instance, according to EnergyStar.gov, an air conditioner does not reach peak efficiency until it’s been running for ten minutes. So if your system is short-cycling, your air conditioner will never be running as efficiently as possible. Ultimately, an oversized HVAC system not only costs more upfront, it will also cost you more in energy bills because it will not run as efficiently as a “right-sized” unit.
Short-cycling is also bad for your comfort because the temperature is your home won’t be steady. Instead you’ll get bursts of heat (if your heater is running) or blasts of chilly air (if your AC is running). A right-sized HVAC unit, on the other hand, will keep your home’s temperature steadier.
Finally, short-cycling can also shorten the life of your HVAC system. Every time your unit starts and stops it puts strain on the motor. Longer cycles mean fewer starts and stops, which will help extend the life of your HVAC.
Ultimately, bigger is not always better when it comes to HVAC. When purchasing a new system, have a trained technician evaluate your home to determine what size HVAC will fit you best. It can save you money upfront and down the road.