Healthy Home

Keep Your Home Healthy

Indoor air quality is important because we breathe about
5,000 gallons of air daily and spend 90 percent of our time indoors. Everyone’s health is affected
by indoor air quality, but children and the elderly are at higher risk
of adverse effects. Indoor air quality problems can be life
threatening, such as exposure to carbon monoxide. Exposure to mold can cause respiratory problems and
can trigger asthma attacks.

Ventilate to reduce moisture and pollutants

Exchanging inside air with outside air is required to remove
pollutants and moisture (when outside air is dry). Ventilation minimizes
exposure to human-generated pathogens such as viruses and bacteria that cause illness.

The recommended ventilation rate for homes is
0.35 air changes
per hour (ACH) or 15 cubic feet per minute per person. For example, a
1,200 square foot home with 8-foot walls has an air volume of
9,600 cubic feet. Obtaining an air change of 0.35 per hour requires
exchanging 0.35 x 9,600 = 3,360 cubic feet of
air per hour. This is an airflow rate of 3,360 ÷ 60 minutes per hour =
56 cubic feet per minute.

Natural air infiltration through doors and windows may provide some air exchange. A heat
recovery ventilator (heat exchanger) is an energy efficient method of
obtaining the recommended air exchange while reducing the cost of heating and cooling the ventilation
air. Lingering odors are one indication
of inadequate ventilation.


Many activities in the home produce moisture that
needs to be
removed. Each person produces about 3 pints of water per day while
breathing. About 1 pint of moisture is introduced into a home during a
10-minute shower. Additional moisture is added by towels drying.

A house will produce 6 to 16 pints of moisture per day as materials in it dry during the fall. Moisture
coming through a concrete basement floor and walls due to moist soil on
the outside may be as much as 100 pints per day. Remove moisture by
ventilation when outside temperatures are cool and with a dehumidifier or air conditioning when outside temperatures are warm.


A major problem with excess moisture in the home is mold. Exposure
to mold can cause cold-like symptoms, respiratory problems, nasal and
sinus congestion, watery eyes, sore throat, coughing and skin irritations,
and can trigger asthma attacks. Children, the elderly, pregnant women
and people with existing respiratory sensitivities are at higher risk
for adverse health effects of mold. If you can smell or see mold, you have a mold problem. Since
people react to mold whether it is living or dead, the mold must be removed.

Mold can be removed from hard surfaces such as hard plastic,
glass, metal and counter tops by scrubbing with a soap or detergent. (Do not
mix ammonia and bleach. The fumes are toxic.) It is impossible to
completely remove mold from porous surfaces such as paper, Sheetrock
(drywall) and carpet padding. These materials should be removed and
discarded. Scrubbing may not completely remove mold growth on
structural wood, such as wall studs, so it may need to be removed by
sanding. Wear personal protective gear and isolate the work area from the rest of the home while sanding.

After the mold is removed from structural
wood, disinfect the
area using a chlorine (sodium hypo chlorite) bleach and water solution
or another disinfectant. The amount of bleach recommended per gallon
of water varies considerably. A clean surface requires less bleach than a
dirty surface. A solution of ¼ to
½ cup bleach to 1 gallon of water should be adequate for clean surfaces.
The surface must remain wet for about 15 minutes to allow
the solution to disinfect. Provide adequate ventilation —
exchanging inside air with outside air —
during disinfecting, and wear rubber gloves. Rapidly dry the surfaces.

Plumbing leaks

Extensive mold growth occurs in areas that stay moist due to plumbing leaks. Check under
sinks, dishwashers and other locations that may have hidden moisture.

Bathroom exhaust fan

Run the bathroom exhaust fan during and for a few minutes
after showers to exhaust the moisture. A timer switch is a convenient method of obtaining the desired
fan run time. You should be able to feel air entering the bathroom under the bathroom door while
the exhaust fan is running. Keep surfaces dry to prevent mold growth.


Closets can be conducive to mold growth. Closets on exterior walls
will be higher in humidity than the rest of the house during the heating
season. The relative humidity of the air in a closet may be at a level conducive
to mold growth, even when the humidity in the house is low, if the
temperature in the closet is cooler than in the house (Figure 1). This will
typically occur near the outside wall. Keep the closet warm by storing things
away from the outside wall to allow air circulation. Leave closet doors
open during very cold weather. Clothes stored in a basement may
become musty, particularly during the summer, if the humidity is
above about 70 percent. Stored clothes should be clean and dry.
Boxed articles will stay wet if they become damp, creating an
environment conducive to mold growth.


Keep furniture away from outside walls to permit air circulation.
Cool areas behind furniture will be high humidity areas conducive to
mold growth. Periodically vacuum upholstered furniture to remove skin fragments that create an
environment conducive to dust mites.

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Figure 1. Closets on exterior house walls may be conducive to mold growth.
Adapted from Moisture Control Handbook: Principles and Practices for Residential and
Small Commercial Buildings by Lstiburek and Carmody. (click on image for a bigger

Basement carpet

Water vapor from moist soil under a concrete basement floor may
come through the floor and moisten carpet. This creates an environment conducive to mold growth. A
carpet pad is discouraged on the floor if there is potential for moisture because the moisture is held by
the pad. Generally mold growth occurs on the back side of the pad and is not visible unless the carpet is lifted.

Clothes dryer

Vent a clothes dryer outdoors. About 5 pints of water are removed per load of clothes. This amount
of moisture could cause severe moisture problems, such as mold growth, if vented into the house.

Flooded materials

Mold will grow on wet materials in 24 to 48 hours. Expose the wet materials to dry airflow to
promote rapid drying. Wall cavities and other closed areas, such as flooring
layers, need to be opened to permit drying before mold growth occurs.

Window condensation

Moisture condenses on windows because the window
temperature is below the dew point of the air in the house. This
moisture can damage the window and wall around the window and lead to
mold growth. Condensation can be minimized by reducing the
humidity level or warming the window surface (Figure 2). Keep the inside
humidity level below about 40 percent in the winter in cold climates to
reduce condensation potential. Lower the humidity level by increasing
ventilation when outside air is
cooler than inside air. Dehumidifiers generally lower the humidity level
to only about 50 percent so are not adequate for limiting
condensation during the winter. The window surface can be warmed by
adding additional layers, such as plastic.

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Figure 2.Condensation on window surfaces as affected by outside temperature, inside relative humidity and window type.

(click on image for a bigger image)

Indoor humidity

Recommended humidity level in the winter is 30 to
40 percent in cold climates. A relative humidity above about 40 percent
the potential for condensation on windows and other cool
surfaces. Humidity levels below about 30 percent lead to dry skin and
nasal passages, increasing the potential
for respiratory illnesses. Overly dry air can inflame the symptoms of
sinusitis, lead to laryngitis and get
in the way of a good night’s sleep. Also, low humidity levels
cause problems in furniture and pianos due to wood shrinkage and
the incidence of static electricity shocks.

During the summer, indoor humidity levels
should be kept below about 65 percent to minimize the potential for mold
growth and below about
50 percent to minimize dust mites.

Hygrometers (relative humidity gauges) may not be accurate. Mechanical hygrometers are
frequently in error by more than 20 percent. Calibrate your
hygrometer by sealing it in a plastic bag along with a cup containing ½ cup of
water and ¼ cup of table salt (Figure 3). After at least 12 hours
at room temperature, the meter should read 75 percent relative humidity. Electronic meters tend to be
more accurate, but they should also be calibrated.


A dehumidifier works best at removing moisture
from warm, humid environments. Many units
are rated at 80 F and 60 percent relative humidity. A 10-degree
in temperature will reduce the capacity by about 40 percent. Therefore, a
dehumidifier rated at 30 pints per day at 80 F is expected to
remove only about 18 to 20 pints at 70 F. A 10-percent increase in
relative humidity is expected to increase
the capacity by about 25 percent. Therefore, a dehumidifier rated at 20
pints per day at 60 percent relative humidity would be expected
to remove about 25 pints at 70 percent relative humidity. Coils should
be cleaned periodically to maintain the dehumidifier’s efficiency.

Basement humidity should be kept at or below about 65 percent during the summer. A dehumidifier or
air conditioning should be used to remove the moisture.
Ventilation during the summer may add moisture to the basement. Outside air
at 80 F and 50 percent relative humidity will be at almost 70 percent
relative humidity when cooled to 70 F in the basement.

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Electronic hygrometer                                                          
Mechanical hygrometer

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¼ cup table salt•½ cup water•5 qt. Ziploc bag. After 12 hours 75% humidity

Figure 3.Calibrate a hygrometer to assure its accuracy.

Attic ventilation

Adequate attic ventilation is required to prevent moisture problems in
the attic, including moist insulation and moisture that can soak through
the ceiling. For natural ventilation, provide 1 square foot of vent area for each 300 square feet of attic area
if there is a vapor retarder (plastic) in the ceiling and 1 square foot of
vent area for each 150 square feet of attic area without a vapor retarder.
Place half of the vent area near the roof peak and half at the eaves.
Provide air chutes or use other methods to assure that eave vents are not blocked by insulation and that
wind does not enter the insulation, reducing its insulating value (Figure 4).

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Figure 4. Air enters for attic ventilation at the eave and exhausts near the roof peak.
Adapted from Moisture Control Handbook: Principles and Practices for Residential
and Small Commercial Buildings by Lstiburek and Carmody. (click on image for
bigger image)

Ice dams

Ice dams occur when escaping heat melts snow on
the roof and the
water freezes when it reaches the cooler surface near the eave. Water
from ice dams can enter wall cavities, causing insulation to be
ineffective, leading to rotting of structural
wood, staining wall coverings and creating conditions conducive for
mold growth. Reduce the potential for ice dams by sealing any air leaks
from the living space to the attic
and providing adequate attic insulation and ventilation
to keep the roof cold (Figure 5).

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Figure 5. Problems caused by ice dams.
(click on image for bigger image)

Crawl space

A vapor retarder must be placed on the soil and sealed to the
foundation to limit moisture from moving into the crawl space. Moisture in
the crawl space will lead to mold growth, which can affect the health of building occupants (Figure
6). The crawl space should have vents to permit ventilation to remove moisture if needed.
The vents are normally closed. The soil on the house exterior should be sloped to carry water
away from the foundation. The crawl space should have drainage similar to a basement.

Home drainage

Install at least 6 inches of gravel underneath the
concrete floor. This forms a water drainage layer and radon removal
layer. Place a vapor retarder between the concrete floor and the
layer to minimize radon and moisture entry into the house. Place
4-inch drainage pipe along both the inside and outside of the concrete
footing. The top of the drainage pipe should be below the top of the
footing. Install a coarse gravel envelope around the outside drainage
pipe. Place filter fabric around the coarse gravel to prevent soil
from clogging the coarse gravel (Figure 7). Place gravel or a
drainage mat next to the concrete foundation wall (basement wall) to
water to drain to the drainage pipe and to keep wet soil away from the
wall. Place a layer of low permeability
soil, such as clay, near the surface to limit the amount of water
soaking into
the ground next to the wall. Slope the ground about 1 inch per foot
away from the house. Extend down spouts several feet away from the
house. One inch of rain on a 1,000 square foot roof is equal to about
gallons of water.

Dust mites

Dust mites are tiny creatures (too small to see)
that feed on human skin cells that we shed each day. Mites may cause
symptoms such
as a runny nose or watery, itchy eyes in allergic people. Dust mites
prefer moist environments and soft
textiles, including sheets and bedding, upholstery fabrics and

Keep humidity levels less than 50 percent and
provide ventilation
to minimize dust mites. Wash sheets weekly in water that is 130 F
or warmer. Mattress pads and other bedding also should be washed
in hot water, but probably do not need to be washed as frequently as
sheets. Periodically vacuum the mattress to remove skin fragments that
create an environment conducive to dust mites. Special pillow and
mattress covers can minimize dust mite exposure. Replace pillows
about every five years. Dust mites do not normally live in the dry
environment of a furnace or air-conditioning duct.

t Pollutants


Studies by the Environmental Protection Agency and the
Consumer Product Safety Commission have shown that cool mist
humidifiers (ultrasonic and impeller) can disperse microorganisms and
minerals into the air. Proper care and cleaning of humidifiers is important
for reducing the potential for exposure to these microorganisms.
Microorganisms often grow in humidifiers equipped with tanks
containing standing water. Follow the manufacturer’s recommendation
for cleaning and changing water in the humidifier. Do not permit the
area around the humidifier to stay wet.

Unheated crawl space                                                                      
Heated crawl space

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Figure 6. A vapor retarder must cover the ground of a crawl space to limit moisture accumulation
and the potential for mold growth.
Adapted from Northern Comfort: Advanced Cold Climate Home Building Techniques.
(click on image for bigger image)


Space heaters

Combustion-type space heaters produce carbon monoxide,
water (almost ½ gallon per gallon of fuel) and many harmful pollutants during the combustion of the fuel.
These combustion gasses must be vented outdoors. Carbon monoxide is
a colorless, odorless gas that can be fatal.

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Figure 7. Foundation drainage system.
Adapted from Moisture Control Handbook: Principles and Practices for Residential and Small Commercial Buildings by Lstiburek and
Carmody. (click on image for bigger image)

Vehicles in attached garages

Vehicles should not idle in an attached garage because they produce large amounts of carbon monoxide and other pollutants
that can enter the house.

Smoke detectors

Place smoke detectors near or in bedrooms and on every floor of
your home. Test smoke detectors at least every three months and
replace batteries as recommended.


Radon is a colorless, odorless, tasteless radioactive gas that increases the potential for lung cancer. Radon has been found
at elevated levels in homes across the country.

Test your home for radon. The testing device, normally a charcoal
canister kit, is set in the lowest habitable space (usually the basement
during the heating season when the house is kept closed) for a few days and
then sent in for analysis. If the reading exceeds the recommended level
of four picocuries per liter of air, further testing will be needed to determine
if there is sufficient radon in the living space to require action to reduce
the level. Test kits are available from some hardware stores, your
local public health district or the American Lung Association.

Reducing radon levels requires a combination of sub-slab
suction using a fan, a sand or gravel layer under the concrete floor and basement floor crack sealing.
Consult Extension Service or other publications for more information.


A furnace should be serviced by a technician every one or two
years. This service should include performing maintenance and checking
for proper operation, including proper combustion and exhausting
of combustion gasses. Combustion gasses contain many pollutants
and can be drawn back into the house if a vacuum is created in the house by an operating fireplace or
large exhaust fan.

The furnace filter needs to be changed routinely to permit adequate airflow through the furnace or air conditioner. The more
porous furnace filters are designed to protect the furnace and have little ability
to remove household pollutants. Common pleated filters
generally capture particles larger than about 1 micron, which will remove most dust and many allergens.

Carbon monoxide

Carbon monoxide is produced during combustion. It is colorless and odorless, and may be lethal. Symptoms of carbon
monoxide poisoning include headaches, dizziness, nausea and
fatigue. Carbon monoxide detectors should be placed on every level of your home and near bedrooms.

Air filters

The most effective and usually the least costly methods to limit
indoor pollutants are source control and ventilation. Air cleaners may
reduce the levels of certain pollutants, but air cleaning alone cannot
adequately remove all the pollutants in a typical indoor air environment.

Since particles float about in the air, they are difficult to live with
and control. Air movement from a person walking around, the furnace or air conditioner, and the
natural convection of warm air rising and cold air sinking causes particles
to swirl about. Some of the particles float in the air, and some settle
on surfaces. Natural settling may be so rapid that air cleaners contribute little additional effect.

The effectiveness of air cleaners in removing pollutants from the air is
a function of both the efficiency of the device itself (the percentage of
the pollutant removed as it goes through the device) and the amount of
air handled by the device. A product of these two factors for a given pollutant is expressed as the
unit’s clean air delivery rate (CADR).

Filters are the most common particle removal
method. The filters are rated based on the size of particles removed.
Other methods
include electrostatic and ion generators. Particles entering an
air cleaner receive an intense positive electrical charge and adhere to
plates, which have to be removed and washed. Ion generators charge
the particles in a room so they are attracted to each other or to
surfaces in the house. Independent tests of ion generators have shown no
reduction in dust concentration in the air. Ozone can be a by-product of
electrostatic cleaners, particularly
if the units become loaded with material, and of ion
generators. Ozone is a lung irritant and should not be used in an
occupied space.

Machines are available that purposely produce
ozone as an indoor cleansing agent. These
should not be used in occupied areas. Ozone, which is an oxidizing
agent, is a potent lung irritant that can cause respiratory distress.
Although residential ozone-generating machines are promoted as air
cleaners, independent studies have shown that the machines do
not effectively destroy microbes or mold, remove odor sources or reduce
indoor pollutants sufficiently to provide any health benefits.

Keep your home healthy through proper home
construction, maintenance and operation.