An HVAC system works at its peak with a good supporting cast: a properly programmed thermostat, well-sealed ductwork and adequate insulation. Make sure these items are in place before you make a purchase decision, as they could actually be the source of your problems. If your central air system is over ten years old, consider replacement.
If your HVAC pro says it’s time for an upgrade, your options depend on a range of variables. It may be feasible to replace the furnace or the AC unit only rather than putting in an entirely new system. But replacing components isn’t always the best option, especially if your system is several years old; the old and new parts may not work together efficiently. You’ll save significantly on labor if the whole thing is replaced at once. No matter what type of unit is most appropriate for your needs, look for Energy Star models, which are about 10 percent to 15 percent more efficient than standard models.
Getting a more efficient system is a great idea, but don’t be tempted to get a larger system than you need for your square footage. A system that’s designed for a bigger house won’t run well and can actually make your house less comfortable because it cycles on and off too much.
Your HVAC system serves as a dehumidifier. An oversized system will cool the house too quickly and shut off prematurely, which means incoming air won’t be completely dehumidified. The combo of colder surfaces and wetter air in your house can cause condensation and mold growth. If mold spreads to drywall or joists, you could face an eye-popping repair bill.