AC Installation and Replacement in Oakland County

What size AC does your house need?

Air conditioners are sized in tons, and one ton is 12,000 BTU of cooling per hour. Home systems typically run from 1.5 to 5 tons. The right number comes from a load calculation, known in the trade as Manual J, which accounts for insulation, windows, ceiling height, which way the house faces and how leaky it is. Square footage alone, or the size printed on the old unit, is not a reliable guide.

Bigger is not better. An oversized air conditioner cools the house quickly, satisfies the thermostat and shuts off before it has run long enough to pull the humidity out. The result is a house that is cool but clammy, with extra starts and stops wearing on the equipment. An undersized unit has the opposite problem and runs all afternoon without catching up. In a humid Michigan summer, sizing is most of what makes a new system feel good.

SEER2 and equipment types in plain English

SEER2 is the efficiency rating for air conditioners, a bit like miles per gallon: the higher the number, the less electricity it takes to deliver the same cooling. For split-system central air conditioners in northern states, the federal minimum at the time of writing is 13.4 SEER2, and standards can change. Higher-rated equipment costs more up front. With a cooling season as short as ours, it takes longer to earn that back than it would in the South, so paying for more efficiency deserves a second look.

How the system runs often matters more to comfort than the number on the label. There are three kinds, and the difference is how many speeds the compressor has.

• Single-stage: fully on or off. The simplest and least expensive, and perfectly good when the system is sized well.
• Two-stage: a low setting for ordinary days and a high one for the hottest. Longer, gentler cycles give steadier temperatures and remove more humidity.
• Variable-speed: adjusts its output continuously to match what the house needs. The quietest and most even, and the most costly.

Matching the new AC to your furnace and ducts

Central air shares the furnace. The furnace blower moves the air, and the cooling coil sits on top of it. So a new outdoor unit has to be matched to an indoor coil of the right size, and the blower has to move enough air for both. One more thing to know: new equipment uses a newer refrigerant than systems built a few years ago. Older systems can still be repaired, but the old and new refrigerants are not interchangeable, which is one reason the coil and outdoor unit are replaced as a pair.

That raises a fair question: should the furnace be replaced at the same time? If it is in the second half of its life, doing both together gives you a properly matched system and one installation instead of two. If the furnace is fairly new, keep it. We will tell you which case you are in. For the combined job, see replacing a furnace and AC together. We also look at the ducts, because ductwork that is leaky or too small will hold back any new system.

Adding central air to a house that has none

If your home has a forced-air furnace but no air conditioning, adding central air is usually straightforward: a coil goes above the furnace, the outdoor unit goes outside and the existing ducts carry the cooling. We check first that the ducts and blower can handle it, since ducts designed only for heat are sometimes too small for cooling, and that the electrical panel has room for the new circuit.

If the house is heated by a boiler and has no ducts at all, there are two routes. New ductwork can be run through a basement, attic or closets where the layout allows. Or ductless mini-splits can cool the house room by room without any ducts. Each has its place, and the house usually makes the choice clear once we have seen it.