It seems just about everyone has basement humidity problems. Where does all that water come from?



Humidity can be naturally present in the air entering your house. In spring or summer this can come in through open windows and doors; when the heat or AC is on it could come from air leakage around windows and doors, or cracks in walls and ceilings. 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 down on moisture is to slow down the fresh air coming inside, especially during humid weather.

Water can seep through basement walls from outside as well. 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, showering, indoor laundry lines, 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.

Keeping the water out

Don't just buy a humidifier if you have humidity problems. You'll save money, improve comfort, and make your home healthier if you tackle the source of the problem, rather than just address the symptom. If a basement renovation or a change in habits can solve or reduce your problem, you won't need a dehumidifier as much, or even at all. So let's start with prevention.

Keeping surface water out

Water pooling in your driveway, or pouring out of your or your neighbor's eaves troughs, or gushing out the downspouts at ground level, will find its way downhill. If there's porous soil around your house, or a crack between the pavement and the house, the water will flow down there until it reaches the water table or an impermeable layer of substrate. Once it can't flow down, it will try to flow across, which is when it hits your foundation walls and starts working its way through.

The first angle of attack is to keep the surface water from collecting around the walls of your house. Start with eaves troughs and downspouts: make sure they are in good working order, are not overflowing or blocked, and that water is drawn away from the house, not leaking onto the foundation.

Ideally, you should disconnect your downspouts and divert the outflow away from the house foundation. This may help reduce soil water levels around the house, if the downspout is flowing into a gravel drainage pit, or if the drainage pipe is cracked. If the downspouts drain into sanitary sewers, disconnecting will also help your city sewage department, which doesn't really need rainwater in its sewage treatment plants.

Even better than just disconnecting your downspouts, install a rain barrel to harvest the rain from your roof so you don't need to use tap water to water your garden or lawn. Just make sure the barrel overflow drains away from the house.

Your driveway should slopes away from your house. If it runs alongside your house, it should slope away both towards the front or back, and towards the side farthest from your house. If your driveway has another house on its other side, it should also have a U-slope from side to side to draw water away from both house foundations.

If there is a narrow gap of soil between your driveway and your house walls, run a line of mortar along the house walls, flush to the wall at the top and wide enough at the bottom to seal the crack. This will keep water from sneaking down the crack.

Finally, if you get a lot of snow, be sure to clear it from the ends of the driveway before a melt so the melt waters can escape out to the yard or the street.

Other areas around the exterior: Gardens, lawns, and other surfaces should also slope away from your home so water drains away from your walls. If you have a sump pump, it should drain away from the house as well.

Keeping groundwater out

Here there are three options, and which one you choose will depend on your budget and whether outdoor digging or inside renovation are possible. The options are: seal walls from the inside, seal walls and floor from the outside, or improve drainage along outside walls and beneath the foundation.

You can hire a waterproofing contractor to dig down to your foundation from outside, and apply a waterproofing compound to the exterior below-ground masonry. They can also fill the dug-out area back in with gravel and sand to improve drainage, and they can install drainage tile to draw the water table down below the floor of your basement. Just make sure they install the drainage tile to drain into the storm sewers or a sump hole with a pump to empty it. Drainage tile won't help if it doesn't connect to a drain!

If you have exposed masonry in your basement, or are planning to remove and replace the drywall, 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.

If you have exposed concrete floors, seal cracks and patch any missing concrete. Humidity can seep in through cracks and exposed sand.

If you are lowering your basement, for example by underpinning or benching it, your reno should include installing drainage tile below the footings, and a sump pit and sump pump.

Reducing moisture production in the home

Moisture you can prevent from being released into the enclosed space within your home will help cut down on basement humidity problems. While you can't stop breathing, changing habits in the kitchen can help. For example, cook with pot lids on when possible, and run the range hood when cooking anything that produces a lot of steam. Keep showers short and run the fan while showering.

Make sure dryer vents in your basement are properly connected and exhaust their air only to the outside. If you dry some of your laundry on a line or rack, do it outside rather than your basement if you think this is contributing to humidity problems.

Fish aquariums and house plants can also contribute to humidity. Keep aquariums well covered, and opt for drought-tolerant plants that need little watering (and therefore don't release much water vapor) and these living things should not be a big part of your problem.

Take out the humidity but not the heat

If you have humidity problems in the winter it may be that your home is sealed too tight. Well-sealed homes are a great way to save on heating and cooling costs - but a house that is too well sealed can cause humidity build up. It can also cause adverse health effects, because inadequate ventilation lets the toxic off-gassing from plastics, foams, paints, even wood build up in the inside air. Consider installing a heat exchanger if your house suffers from being too well sealed. Heat exchangers allow air to flow in and out of your house, while capturing most of the heat on its way out. Especially when outdoor temperatures are below freezing, outdoor humidity is typically lower than that inside a well-sealed home that has humidity problems.

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.

There are two capacity rankings for a dehumidifier: extraction capacity, which is the amount of water they can extract from the air each day, and tank capacity, which is how much water the tank can 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.) This is especially useful if you're away for several days during times of high humidity ? for example, a summer vacation.

If running a hose isn't an option, make sure you buy a unit with adequate tank capacity for the humidity of your basement given how often you think you'll be willing or able to empty it.

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.

This measurement goes in the opposite direction from most other appliance energy factors, where the energy factor measures energy consumed in a year, rather than amount of work done per energy unit. The key to remember is that a higher energy factor is better.

The ENERGY STAR website lists dehumidifiers whose energy factor ranges 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. Therma-Stor-manufactured, high-energy factor dehumidifiers also include some products rebranded by Ultra-Aire (the most efficient of all at 3.56), Honeywell, Basement Systems, and Santa Fe.

Dehumidifiers rated by the Canadian Office of Energy Efficiency have Energy Factor ratings between 2.02 (best - only one model, the Bionaire BDQ25-UC) and 1.00. EnerGuide energy efficiency cards are not provided on dehumidifiers sold in Canada, so read the Energy Factor rating carefully on the product spec sheet or packaging.

Don't be misled by an ENERGY STAR label. Bear in mind that an ENERGY STAR rating on a dehumidifier does not mean it is really energy efficient - just more energy efficient than some of the others in its category. For example, in Canada, the OEE lists ENERGY STAR-rated dehumidifiers with an energy factor as low as 1.2, when the best energy factor is 2.02 and the worst is 1.0.

Choosing the right extraction capacity

Always buy a dehumidifier that cam handle the level of 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. But remember that, given two ENERGY STAR rated dehumidifiers, the higher capacity unit is typically more energy efficient because of the different capacity thresholds by which ENERGY STAR rates dehumidifiers. It probably makes sense to buy a higher-capacity dehumidifier than the guidance suggests, so you can get the higher energy efficiency rating that comes with it.

Relative humidity - what it means, what you should target

Relative humidity or RH is a measurement of how close the air is to saturation with water vapor. At 100% relative humidity, water begins to fall from the air naturally. For a house the objective should be to keep the relative humidity between 30% and 50% (warmer weather) to prevent bacterial growth, or between 30 and 40% (cooler weather) to prevent frost or condensation buildup on windows.

Digital dehumidifiers have a built in humidistat to measure relative humidity, and you can set the target humidity digitally to a specific level. This is much more precise than the target humidity level allowed by analog dehumidifiers. Especially if you have an analog dehumidifier, buy a hygrometer (humidity meter) from your local building center to measure the RH in your home, and to determine whether your dehumidifier is set properly for the target humidity level.

Extra-cold basement? Get the right dehumidifier for the job.

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. You can buy ENERGY STAR rated dehumidifiers that can operate as low as 42F or 6C.

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. When vacuuming your basement, vacuum the coils. Some dehumidifiers include a washable air filter you can clean to remove dust build-up; this filter prevents the dust from reaching the coils.

How much energy can you save?

If you replace an old dehumidifier with a new, ENERGY STAR rated dehumidifier of a high enough daily capacity, and you address the sources of humidity in your house to the best of your ability, you could cut your energy use by half or even two thirds over what you were paying before for the same humidity control.

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 more detailed information, see the dehumidifiers article at Green Energy Efficient Homes.