Control Indoor Humidity with Right Size Home Air Conditioner

The two most important factors for maintaining indoor comfort are air temperature and relative humidity. Southerners understand the impact of humidity on comfort and dehumidifiers are popular to control indoor humidity at any given temperature. Experts say indoor relative humidity should be maintained between 40% and 60%.

Managing comfort with dehumidifiers come with costs – the first cost of purchasing the equipment and the ongoing operational cost, which can be substantial. An economical way to save money and manage indoor humidity is with your central air conditioner system instead of buying a dehumidifier unit.

Dehumidification is a by-product of cooling humid air. Managing indoor humidity with your air conditioner requires a whole-house approach that uses building science for sizing the air conditioner unit.

The amount of humidity your air conditioner will remove depends on how long the system runs, so this strategy requires installing an air conditioner that is just the right size for the home and local climate. Systems that are too big (as size is measured in “tons”) will quickly cool the indoor temperature, but they don’t run long enough to substantially lower humidity.

Many HVAC contractors would rather sell you a large capacity cooling unit and a dehumidifier because it is more profitable, but contractors are mainly concerned about complaints from clients on the hottest days of the year. Right-sizing is a trade-off between better humidity control through spring, summer and fall or having an oversized cooling unit that will maintain a 68 degree indoor temperature on the hottest few days of the year.

In an attempt to address humidity issues, many manufacturers are offering thermostats with humidity control that try to maximize the latent removal capacity of air conditioning systems. These systems typically will drop the temperature set-point by 2 degrees to force the cooling system to operate. This is an improvement, but it requires a thermidistat and a variable speed air handler. If oversized, this system will quickly reach that 2 degrees of cooling and shut off without significantly removing moisture.

The choice between oversized capacity to meet full demand on the hottest day of the year or a right-sized cooling unit that will save money and deliver better comfort all year long may seem difficult, but consider this. If on the hottest day of the year when it’s 102 outside with 90 percent humidity, a right-sized central air conditioner may only be able to achieve 78 degrees indoors. Studies have shown that occupants are agreeable to higher indoor temperatures when the humidity is controlled. You may feel even better when you receive a monthly electric bill that doesn’t leave you hot and bothered.

Still there will always be those in the HVAC industry that believe right-sizing is actually under-sizing or that it is an energy efficiency measure that disregards comfort. Participating AlabamaWISE contractors use right-sizing to maximize comfort and minimize monthly summer electric bills.

Alabama residents pay some of the lowest electric rates in the country, but use 30% more energy than the average American. Right sizing your replacement heat pump or central air conditioner will help you enjoy better indoor comfort and reap the benefits of low electric rates by cutting energy waste.

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