The dehumidifier is a kissing cousin to the air conditioner (AC). The dehumidifier is specifically designed to remove water from the air. The AC is designed to remove water and heat from the air. The humidity in the air is measured as relative humidity (RH).
Moderately, dry air (30 to 50% RH) works wonders in a home. People feel best in this interior humidity range. Dryer air keeps people more comfortable at a higher temperature. When humidity creeps up, people tend to turn up then AC. The dehumidifier is a useful tool for helping homes in the comfort zone (the combination of temperature, humidity, and air movement which keeps a room comfortable).
Dry air is an effective mold, mildew, and dust mite deterrent, and thus is crucial to a healthy home. Most molds need 70% RH to get started. Dust mites grow best at 75-80% RH, and they cannot survive when the humidity is below 50%.
Other common home humidity problems arise in damp basements, unventilated kitchens and baths and leaks. Unventilated kitchens and bathrooms dump moisture into the air that your AC system is expected to remove. Damp foundations, basements, and crawlspaces, leaky roofs and misplaced drainpipes, leaky plumbing are also moisture culprits. In some cases, the greatest humidity source is damp outside air seeping into the house.
In hot, humid climates, the AC systems are designed to both cool and dehumidify. But sometimes the ACs is oversized to cool during extreme heat conditions. As a result, under normal conditions, the AC runs too few hours to effectively dehumidify the air, and interior humidity builds up. The dehumidifier is a good fix for this condition. Ultimately, however, the AC system should be re-engineered before replacement.
Dehumidifiers work better in high humidity and temperatures conditions. Most don’t work well at temperatures below their rated working range, listed in their spec sheet. For example, a humidifier rated at 65o F will not work swell in a 40o F basement.
A home dehumidifier typically removes 2 to 10 gallons or water daily from the air. They work from condensing moisture from the air onto a cool coil. For example, the air mass in a 1,000 square foot home at a temperature of 80oF and 60% relative humidity (RH) contains 10 gallons of water. If 2 gallons of water were stripped from the air the RH would drop below 50%.
This work of stripping water from the air comes at a steep energy price in kWh. In our Florida neck of the woods, it costs about ten cents to dry a towel with air conditioning…about a third of that to dry it with a dehumidifier…and a lot less than to throw it in a clothes dryer vented to the outside.
So it makes sense to limit both internal and external sources of humidity at the source first. Moisture source control strategies for these problems include weatherization-moisture control; bathroom vent fan; kitchen vent fan; home air sealing and sealed attic.
The choice of an energy-efficient dehumidifier is a daunting task. The capacity is given is U.S. liquid pints per day which a dehumidifier can remove from the air. The efficiency factor is liters per kWh. This is confusing enough. But it gets more complicated!
As a rule of thumb it is best to get the largest capacity dehumidifier which is practical. As the table below shows, a 70 pint capacity dehumidifier costs about the same to operate as a 35 pint model. However, it will run 50% less of the time and thus make less noise and potentially last longer. A unit which is undersized and running almost continuously may burn out in three years or less. Also, the extra capacity may come in handy in a prolonged hot humid spell, or in case of an unforeseen leak into the house.
There is one thing which is clear. Choose an Energy Star rated model. They may cost little or no more than a conventional model, while saving substantial electricity.
A ceiling fan creates a “wind chill” factor that allows people (and your pets) to remain cool at temperatures above 750F. The fan breeze strips away hot air from the surface of your skin, and enhances evaporative cooling of your sweat.
A ceiling fan uses energy a lot less energy than an air conditioner.
It enables the homeowner to set the thermostat at a higher setting, and reduce the number of hours your energy hog of an air conditioner has to run.
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