Back in 2009, I had a new air conditioner installed our condo. It wasn't cooling much, and the summer electric bills had risen. So, I did a Manual J load calculation on our condo to find out what size we should replace it with. There's this thing called summer design temperature, which is the temperature that your location goes above only 1% of the time. As I wrote in an earlier article about how to find out if your AC is oversized, I wanted to go with the 1.5 ton AC, but I chickened out and put in a 2 ton unit instead. Our place is about 1500 square feet, so that's 750 square feet per ton. That day was last Friday, 29 August, and I looked at the 24 hour period from midnight to midnight.The thermostat was at 75° F for nearly the whole day. The only time it wasn't was in the early morning morning when I lowered it to 74° F. Our design temperature in Atlanta is 92° F. Last Friday, we had a good 5 hours when the temperature stayed right there around 91-92° F. We had another couple of hours above 89° F, so it was perfect for seeing if our AC is oversized.

From 6 pm to 7 pm, the AC was on for 31 minutes and off for 29. Note that the graph above isn't showing the actual on/off cycles. Over the whole 24 hour period, the air conditioner went through 35 cycles. How to Tell If You Have an Oversized Air ConditionerIn addition to being uncomfortable, humid indoor air also causes damage to your home and furnishings and promote the growth of mold and dust mites. Thankfully, purchasing a quality dehumidifier is a great way to solve the problem. Controlling humidity levels is important. Relative humidity shouldn't exceed 40-50%. Learn the basics here, and determine if you have a household moisture problem.and if using a dehumidifier is right for you. If you notice creaking floors, condensation developing on windows, or exacerbated allergy symptoms then your home's humidity levels may be too high. Those living in hot, humid climates may also find that their homes provide the optimal environment for pests such as termites. The chart below illustrates how humidity levels can affect your health and home:High Humidity (Use Dehumidifier) Low Humidity (Use Humidifier) Stains on Ceilings and Walls Scratchy Nose and Throat Condensation on Windows and Mirrors Damage to Electronic Equipment Damage to Home and Furnishings Damage to Home and Furnishings Continued Respiratory Discomfort  Humidity is often associated with that muggy feeling you experience on a warm summer day.

There are two forms of humidity: absolute humidity and relative humidity. Absolute humidity refers to the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. As such, the hotter the air, the more water it contains.mobile office hvac unitOn the other hand, relative humidity refers to the ratio of the current absolute humidity to the highest possible absolute humidity. diagram of hvac split systemIf an environment has 100% relative humidity, this means the air is saturated with water vapor and can hold no more moisture. ac unit condensationThis creates the possibility of rain.Overall, humans are quite sensitive to humidity because the skin relies on air to get rid of moisture. Sweating is your body's way of keeping cool and maintaining its current temperature.

This is why you feel hot and sweaty when humidity levels are high.When there is low relative humidity, you feel much cooler than the actual temperature because sweat is quickly evaporating and cooling us off. In other words, if the temperature is 75° F with zero relative humidity, it will feel like it's 69° F. If  relative humidity is 100%, it will feel like it's 80° F. According to the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standard Environmental Conditions for Human Occupancy, it is recommended that relative humidity be kept between 30% to 50% in the summer and 30% to 40% in the winter.In order to measure humidity levels, you can purchase a small, inexpensive hygrometer. This device will confirm whether there is too little or too much humidity. Once you are aware of the humidity levels in your home, you can then decide if you need to take action.To get an idea of the human perception of humidity, look to the chart below:Relative Humidity at 90° F Very Humid and Uncomfortable Somewhat Uncomfortable for Most People Acceptable for Most;

Some May Perceive it as the Upper Limit May Feel Slightly Dry to Some People Again, if your air is too dry, you can regulate moisture levels with a humidifier. However, if your air is too moist, a moisture removal system can help maintain the indoor relative humidity at the desired level, control musty odors, and protect furniture from water damage.Dehumidifiers are household appliances that help reduce the humidity levels in the air. There are primarily two types of humidifiers: desiccant and mechanical.DesiccantDesiccant Models are named for their use of a desiccative or drying substance to remove moisture from the air.The dehumidifying process involves exposing the desiccant matter to an air stream with high relative humidity. These units do not use compressors and are best placed in areas with low temperatures and lower humidity levels. They are inexpensive and quite effective when controlling light humidity problems.  MechanicalMechanical Models are much more common.

These units are like air conditioners, containing both hot and cold coils in the same box. As the fan draws indoor air over the cold coil, the moisture is collected into a bucket. Dry air then passes through the hot coil to warm it back to its original temperature. As a result, mechanical units raise the air temperature slightly, as opposed to air conditioners, which cool the air as it dehumidifies it.  This model is ideal for moderate to high humidity levels.There are several factors to consider when shopping for a moisture removal system. Consider the size of the unit, dehumidification capacity, and safety features. Below is a list of some of the most common things to look for when choosing a moisture removal system and what it means to you.Size: The size of a dehumidifying unit is generally based on the amount of moisture extracted from the air in 24 hours,. This is usually measured in pints. Purchase a larger capacity model over a smaller one because larger units can dehumidify more area in a shorter amount of time.

A model with a smaller capacity may run continuously and still not lower the humidity to proper levels. The AHAM, or Association of Home Appliance Manufacturers, recommends the following size guidelines:AHAM Dehumidifier Sizing Guidelines - Match Room Size to Current Humidity Conditions to Find Minimum Size Ratings Condition Without Dehumidification Moderately Damp with Musty Odors in Humid WeatherVery Damp with Odors and Damp Spots on Walls and FloorsVery Wet with Sweating Walls and/or Seepage Extremely Wet with Wet Floors and High-Load Conditions Portability: If you're looking to move your unit from room to room, look for one that is compact, lightweight, and includes a carrying handle or rolling casters.Built-In Humidistat: If you'd like to be able to adjust humidity levels, find an option with a humidistat. This feature will automatically turn the unit on/off depending on the humidity setting.Automatic Shut-Off: This function will allow you to turn the unit on or off without having to unplug it.

It also prevents overfilling when the storage tank is full.Low Temperature Operation / Automatic Defrost:  If you're using it in temperatures colder than 65° F, look for a unit that has an anti-frost sensor. You want ot make sure it will operate in cold temperatures. This prevents quick cycling and frost from accumulating on the sensor.Storage Tank Capacity: Almost all types have storage tanks for the collected water. If you're not planning to purchase a model with a continuous drainage port, you'll have to empty the tank periodically. Continuous Drainage:  Models with a continuous drainage port eliminate the hassle of emptying a condensation tank. Simply attach a hose to the dehumidifier and the moisture will drain out through the hose.Washable / Removable Air Filter: Units that have washable filters trap airborne dust and particles. If the filter is washable, this makes maintenance a breeze: simply pull out the filter; rinse it with mild soap and water; and put it back.Brand: There are several brands available, so if you're loyal to a particular one, this may be something to consider.