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How Air Conditioning Humidistats Work

AC humidistatYour air conditioning system controls your indoor environment in three ways. First, it cools your home, then it regulates the humidity level by removing excess moisture in the interior air. Finally, it heats your home with a heating coil or by operating in reverse function if it is a heat pump type unit. All air conditioning systems use a thermostat to regulate these functions. In some systems a humidistat may also be present.

When your air conditioner is running warm interior air passes over a metal coil which is cold and thus the air is cooled. When passing over the coil moisture in the air also condenses on the cold coil and drips into a pan and is drained to the exterior. A correctly sized A/C unit will remove the proper amount of moisture as it cools the air to keep the interior environment comfortable.

Most people enjoy an interior temperature between 74° and 76° and an air conditioner operating at these temperatures will keep your humidity below 60% which is within the comfort range. If you are a seasonal occupant, you can save money by keeping your air conditioner set to a higher temperature when you are away. But, with your A/C operating less there is a possibility of the interior humidity increasing to levels where mold can begin to form. When your humidistat turns on your air conditioning system will operate in its normal mode cooling and removing humidity in the interior environment.

When there are no people in residence interior temperature levels will rise and fall in conjunction with the exterior temperatures and your thermostat will keep them within the safe zone. Because there are no exterior doors being opened, showers being taken or people breathing and perspiring the humidity levels are slower to rise. But unlike temperature the humidity level will not fall with the exterior environment and over time it will increase to the danger zone. If your interior temperature is set to 80° your home could be in the danger zone for mold growth. If a humidistat is wired into the system, it can be set to turn on when interior humidity increases to levels where there may be a concern for mold growth.

AC Condensation removalIn most situations the humidistat is the primary regulating device and the thermostat operates in a secondary function. If this is the set up in your dwelling, when you are in residence you should set the humidistat to the “ON” position so it will not override the thermostat when a particular humidity level is reached. Then set your comfort level with the thermostat temperature setting. When you go away for the summer season you can set your thermostat to a higher level than would normally be comfortable. Suggested temperature levels vary but you should keep the thermostat setting below 80°. Then, you can set your humidistat to 60%. Typically mold and mildew will not grow below 68% humidity. This combination will save you money on your cooling bills, extend the life of your air conditioning equipment because it will be operating less and keep your interior environment within safe humidity levels thus preventing mold growth.

Some may consider the difference in temperature settings insignificant but when considering that outside summer temperature in South Florida can average 90° or more in the day time, setting your thermostat to 80° as opposed to a comfortable 74° could in theory save almost nearly 1/3rd the energy costs of cooling a large home. If that level of savings is not attained a 20% reduction in energy costs would still be a significant difference.

The down side to a humidistat is many people and especially guests do not understand how to set one when they leave. Sometimes, when your guests leave they may set the two devices improperly with the most dangerous being turning the thermostat off thinking the humidistat is all that needs to be set. With the thermostat set to off the air conditioning will not run at all and dangerous indoor temperature and humidity levels could be reached quiclky. It is also questionable how much energy is actually saved in smaller mulita story condo type units by using a humidistat as opposed to just setting your thermostat to 78°.

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