Air Conditioning Installation – Why Not Oversize?
When an air conditioner runs, it does two jobs. It lowers the temperature of the air, and it removes moisture from the air… Water vapor condenses on coils in oversized air conditioners, too, but you have to get enough condensation on the coil for the water to start dripping down into the pan below the coil.
It takes about 15 minutes of runtime before you start getting serious dehumidification of the air, so oversized systems will not dehumidify well. If the AC comes on, runs 10 minutes or less, and then shuts off, the house may be cool, but in a humid climate, the indoor humidity levels will stay high, probably over 60%.
A properly functioning central A/C unit should be able to cool a moderate, four-bedroom home by 10 degrees Fahrenheit in three hours. Although the cooling power of your A/C also depends on the power, size, and age of your unit, your home should be noticeably cooler within a few hours.
The best way to size your system is to have a “Manual J” calculation done on your house. That’s the gold standard for system sizing, taking into account things like how much insulation you have, what kind of windows and what direction they’re facing, and everything else. Many utility companies will do this for free (check with them), and if not, you can hire an energy auditor. Don’t go with an HVAC contractor for the Manual J, go with your utility or an energy auditor so you can trust that they did it right. They’ll tell you exactly what size you need, and you can shop accordingly.
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