By
Robin Green
Is your basement or apartment damp or musty? Before you rush off to buy a dehumidifier, you should understand where that humidity is coming from, and how the efficiency ratings for dehumidifiers work. With this knowledge in hand, you'll have a dryer home without spending a fortune on electricity or on a dehumidifier you might not need!
It seems just about everyone has basement humidity problems. Where does all that water come from?
Keeping water out
Humidity can come into your house naturally in the air, in spring or summer through open windows and doors, and through air leakage when the heat or AC is on, such as poorly sealed windows and doors, cracks in exterior wall plaster in older houses, or cracks in upstairs ceilings or attic hatches. Anything that draws air out of your house, such as a wood fire, kitchen fan, or a low- or mid-efficiency furnace, will also draw air in.
So one way you can cut moisture is to restrict the flow of fresh air, especially during humid weather.
Water can seep through basement walls from outside. You need to direct surface water away, seal the outside of the foundation, improve drainage below the foundation, and possibly seal the inside of the masonry wall as well.
Human activities such as breathing, sweating, showering and cooking, can also create moisture when the house is closed up. This can add as much as 20 gallons of water a day to your house.
Water pooling in your driveway, or pouring out of an eaves trough, finds its way downhill. If there's porous soil around your house, or a crack between the pavement and the house, the water will flow through the soil or crack until it reaches the water table or is otherwise stopped. Once it can't flow down, it flows across, which is when it starts seeping through your foundation.
So keep surface water from collecting around the walls of your house. Keep eaves troughs cleared of leaves and properly angled, and downspouts in working order with their outflow directed away from the house. Your driveway should slope away from your house, or you can run a bead of mortar along the wall between the driveway and the house to keep water that accumulates in the driveway from working its way down along your foundation walls.
Gardens, lawns, and other surfaces should also slope away from your home, and if you have a sump pump it should drain well clear of the house as well.
Keeping groundwater out is a bit more challenging and can be expensive. A waterproofing contractor can dig a trench to your foundation from outside, and apply a waterproofing compound to the exterior below-ground masonry. They should also backfill the trench in with gravel and sand to improve drainage, and they can install drainage tile at the bottom to draw the water table down below the floor of your basement.
A cheaper option, if you have exposed masonry in your basement, is to scrub down the masonry to a hard, clean surface free of grit or mineral sweat, and use a parging compound - a thin mortar slurry - to improve the waterproofing on the inside of your walls. This works for minor humidity problems but is not a solution if you have serious basement moisture.
Reducing moisture production in the home
Any moisture you can avoid producing will help cut down on humidity problems. You can't stop breathing, but you can cook with pot lids on, and run the range hood when boiling water; you can have shorter showers or run the bathroom fan when showering; and watch out for aquariums, houseplants, decorative fountains, and other possible humidity sources.
Take out the humidity but not the heat
If you have humidity problems in the winter and your home is recently built and well insulated, it may be that your home is sealed too tight. A well sealed home saves on heating costs, but if it's too well sealed humidity will build up, as will off-gassing from plastics, woods, carpets, and other materials that may harm your health. A heat exchanger might be a better choice than a dehumidifier if this is your problem. Heat exchangers allow air to flow in and out of your house, while capturing most of the heat on its way out.
Energy efficient dehumidifiers primer
Let's cover how humidifiers work, their capacity rankings, how energy efficient dehumidifiers are rated, and how to choose the best one for your situation.
Dehumidifiers remove moisture from the air using a compressor, condenser coils, and fan. They work much like refrigerators, except that their cooling power is used to condense water out of the air. They have a humidistat which keeps them running until the moisture reaches a set lower threshold, or until the tank is full, whichever comes first.
Dehumidifiers are ranked based on extraction capacity - how much water they extract from the air in a day - and tank capacity - how much water they hold. In the US, extraction capacity is rated in pints per day and capacity is rated in quarts. In most other countries, extraction capacity is rated in liters per day and capacity in liters.
Once your tank is full, it will not extract any moisture until you empty it. If you place your dehumidifier near a basement floor drain, you can run a hose from the tank to the drain, so that you never have to empty the tank. (Most dehumidifiers come with an opening for a hose.) If running a hose isn't an option, make sure you buy a unit with adequate tank capacity.
Energy factor rankings
The energy factor for dehumidifiers is the number of liters or pints of water removed from the air per kilowatt hour (kWh) of electricity used. The higher the energy factor value, the more efficient the dehumidifier is. So bigger is better - unlike the efficiency rankings for other types of appliances.
ENERGY STAR dehumidifiers have energy factors ranging from 3.56 (the best) to 1.2 (the worst) with a median rating of 1.62. Only two manufacturers, Therma-Stor Products and Munters Corporation, make dehumidifiers with a factor of more than 2.2.
But bear in mind that an ENERGY STAR rating does not mean the dehumidifier is really energy efficient - just more energy efficient than some of the others in its category. For example, ENERGY STAR rated dehumidifiers can have an energy factor as low as 1.2, while the best energy factor is 2.02 and the worst for a non- ENERGY STAR rated dehumidifier is 1.0.
Always buy a dehumidifier that can handle the dampness in your home. You will typically not require a pints-per-day rating greater than 25 unless your basement is extremely wet and at least 1,200 square feet in area, wet and at least 1,500 square feet, or usually damp and musty (but not wet) with at least 1,800 square feet.
On the other hand, higher capacity ENERGY STAR units are typically more energy efficient because of the different capacity thresholds by which dehumidifiers are rated. So don't skimp and buy too low a capacity unit - overestimate rather than underestimate.
If your basement is very cool, get a dehumidifier model that can withstand lower temperatures. Otherwise, the cold basement will cause frost buildup on the coils, which will make them less efficient and may cause rapid on-and-off cycling of the motor. If you hear this behavior, turn the dehumidifier off until the ice has melted and fallen away. If the behavior persists you may need to switch to a unit designed for cooler temperatures.
Cutting energy costs, with whatever dehumidifier you use
If your basement is damp, and you're running the dehumidifier, keep the doors to the basement closed so moist air doesn't creep in from upstairs.
Keep your dehumidifier coils and fan clean and free of dust. Some dehumidifiers include a washable air filter you can clean to remove dust build-up; if you have one, keep it clean.
If you replace an old dehumidifier with a new, properly sized ENERGY STAR rated dehumidifier, and you tackle your humidity sources as best you can, you could cut your energy use by half or even two thirds over what you were paying before for the same humidity control. But more likely, you'll use a little less energy with a replacement dehumidifier, while getting much better humidity control, or you'll use more energy (if you didn't have a dehumidifier) but you'll be far more comfortable.
Given how much evidence is turning up about the ill health effects of indoor humidity and the resulting mold and mildew, you'll definitely benefit from taking control of your humidity problems and buying an energy efficient dehumidifier. You can't put a price on good health!
For other tips on cutting humidity in your home, and for details on ENERGY STAR ratings of dehumidifiers, see
Energy efficient dehumidifiers at GreenEnergyEfficientHomes.com.
By Kunal Sutar
