If your house gets cold but still feels damp or sticky, and the air has a faintly musty smell when the system kicks on, there is a good chance your air conditioner is too big for the house.
That sounds backwards. It is also the most common and most expensive mistake made when a system gets replaced in South Florida.
Your AC has two jobs here, not one
Up north, an air conditioner mostly just lowers the temperature. In South Florida it has to do that and pull a serious amount of moisture out of the air, and the second job is what makes a house actually feel comfortable. A home at 76 degrees and 45 percent humidity feels better than the same home at 72 degrees and 65 percent humidity, and it costs less to run.
Removing moisture takes time. The air has to keep passing over a cold coil, long enough and often enough for the water to condense and drain away.
What happens when the unit is too big
An oversized system cools the air fast, hits the thermostat setting in a few minutes, and shuts off. That is called short cycling, and it means the coil never stays cold long enough to do the dehumidifying half of the job.
The result is a house that is cold and clammy at the same time. You end up turning the thermostat down further chasing a comfortable feeling you never quite reach, which runs the bill up. Meanwhile all that stopping and starting is hard on the compressor, the part you least want to replace, and the standing humidity is what leads to musty smells and mold along vents and returns.
An undersized system has the opposite problem and simply cannot keep up on the hottest days. Both are bad. The right size is the goal, and the right size is usually smaller than people expect.
How homes end up with the wrong size
Most of the time it is not deliberate. A contractor sees a 4 ton unit sitting there, quotes a 4 ton replacement, and never asks whether the original was sized correctly in the first place. Others round up on purpose, figuring a bigger unit is safer in Florida heat. Neither approach looks at the actual house.
What should happen instead
A proper replacement starts with a load calculation, which the industry calls a Manual J. It accounts for square footage, ceiling height, window size and which direction they face, how much insulation is in the attic, the condition and layout of the ductwork, and how many people live there.
Here is the part worth knowing before you spend money on a new system. That calculation is affected by the rest of your house. If your ducts are leaking 25 percent of their air into the attic, or the attic insulation is thin and settled, the calculation says you need a bigger system to overcome those losses. Seal the ducts and bring the insulation up first, and the house often needs a smaller, less expensive unit that runs longer, dehumidifies properly, and lasts longer.
That is why we look at the attic and the ductwork before quoting a system, not after. It changes the answer, and it frequently saves money on the equipment itself.
What to ask whoever quotes you
Whether you use us or not, get a few quotes and ask each one the same questions. Did you do a load calculation, or did you match the existing unit? Did you look at the ductwork and the attic insulation? What is the total installed price including permits, the electrical, and haul away of the old system? What is covered by the labor warranty and for how long?
The answers will tell you a lot. A contractor who did not go into the attic does not actually know what your house needs.
Fall is the right time to do this
In peak season, replacements happen in an emergency, on whatever equipment is on the truck, at whatever price is available that day. In the cooler months you have room to get real quotes, compare them properly, and have the work done on a schedule that suits you, before next summer instead of during it.
A Kool Saver is a licensed Florida mechanical contractor handling AC, ductwork, and insulation in house, so the system gets sized against the real condition of your home. Serving Miami Dade, Broward, and Palm Beach. Get a free quote, or read more about our AC services, ductwork, and attic insulation.