Ever since the oil crunch of the 1970 s, homes have been built with increased insulation and tightened against air leaks. The goal was — and still is — to conserve energy and thus cut cooling and heating bills. But in recent years, builders and residents have come to realize that ventilation is vital, too, because an airtight house can trap contaminants indoors. And indoors is where we spend almost 90 percent of our time, with 65 percent of that in our houses or apartments, according to the National Safety Council.
Indoor levels of pollutants may be two to five times higher — occasionally 100 times more — than outdoor levels, the council says. There is a connection between poor indoor air quality and the fact that the number of Americans with asthma has increased almost 60 percent over the past three decades, to 20 million (6 million of them children under 18 ), according to the American Lung Association. More than 28 million suffer from hay fever and other allergies as well as other airborne illnesses. And inhouse contaminants can contribute to cancer. Poor indoor air quality may occur even in a seemingly spotless home — not that it doesn’t help to vacuum, change air filters regularly, clean dehumidifiers according to instructions, and maintain air conditioning and heating equipment, gas appliances and such.
But bathrooms, damp basements, carpets, furniture and kitchen cabinets, as well as activities like cooking, cleaning and remodeling, produce pollutants. So do many everyday products found in homes.
The answer is ventilation — proper air circulation in and out of the house. Homes built before the 1970 s have a built-in system: leaks through which outside air infiltrates.
“The average house in the United States has about three square feet of holes in it, but infiltration is a pretty bad way to ventilate because it wastes a tremendous amount of energy,” writes Max H. Sherman in the April / May issue of Fine Homebuilding magazine.
Sherman is a consulting building scientist and physicist at Lawrence Berkeley National Laboratory in Berkeley, Calif. He headed a committee of the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE ) that developed standards for ventilation and indoor air quality for low-rise homes and apartment buildings. (ASHRAE is a nonprofit technical organization that sets standards for indoor air quality in all types of structures, even airplanes. )
Opening windows isn’t the solution, particularly in states like Arkansas where for most of the year that means letting in hot, humid air ridden with dirt, pollen and other allergens. The most effective answer, writes Sherman, is to close leaks but build in mechanical ventilation and passive vents that exhaust old air, suck in outdoor air (maybe not ideal in Arkansas ) or do both (balanced ventilation ). Here are some of the main sources of and kinds of contaminants. Combustion: Tobacco smoke, auto exhaust from attached garages, smoke from a fryer or indoor grill, fuel-burning heating equipment, gas water heaters, fireplaces, wood-burning stoves, gas ranges, candles and malfunctioning equipment. Emissions can include carbon monoxide, carbon dioxide, nitrogen dioxide and airborne particles like soot and unburned fuel.
Microbiological: Molds, mildew, bacteria, viruses, dander and saliva from pets or pests, dust mites, cockroaches, pollen. Standing water, water-damaged materials and undetected plumbing or roof leaks can create a breeding ground for molds, which feed on dampened glue found in drywall. Dust mites thrive in moist, warm environments. Radon and soil gas: Radon is a colorless, odorless, radioactive gas that comes from the natural breakdown (radioactive decay ) of uranium, found in almost all soils and rocks. Radon is not a major problem in Arkansas. Soil gas can contain toxins from pesticides or landfill and sewer gas. Other particles: Lead and asbestos may be found in older homes in pipe and furnace insulation, asbestos shingles, millboard, textured paints and other coatings, and floor tiles. Many homes built before 1960 contain leaded paint; old household plumbing was made with lead materials. Volatile organic compounds: Paints, paint strippers, adhesive removers, aerosol spray paints, varnishes, wax. Many cleaning, disinfecting, cosmetic, degreasing and hobby products. Pesticides, air fresheners, nail-polish remover, dyes, plastics, perfumes, printers, copy machines, dry-cleaning chemicals. Formaldehyde, found in adhesives in particleboard, hardwood plywood paneling, fiberboard used for drawer fronts, cabinets, furniture tops, many kinds of carpeting. Volatile organic compounds are used to add permanent-press qualities to clothes and draperies and as preservatives in some paints and coatings.
Air pressure can add to indoor air quality problems. If air is blown into a tight house, it pushes inside air into wall and ceiling openings where it could pick up contaminants. If it’s sucked out from something like a huge range hood, air infiltrates through chimneys, flues or other openings, pulling contaminants into the house. This is called backdrafting. Except for inexpensive radon testing kits, available in home centers and hardware stores, it’s not easy to identify poor air quality. If you’ve moved into a new house or have remodeled or refinished a home and become uncomfortable or developed health problems, consult a doctor or allergist to see if your home’s air could be the source.
Look for signs of poor ventilation: Moisture condensation on windows or walls, smelly or stuffy air, dirty central heating and air conditioning equipment, areas where books, shoes or other items become moldy, and whether you feel better after you leave your home rather than when inside it. ASHRAE’s standards, meant to apply to new as well as existing homes and small multifamily buildings, describe the minimum requirements needed to provide basic indoor air quality. They include: An overall ventilation rate of 50 cubic feet per minute (cfm ) for the average 2, 000-square-foot house and more as house size increases.
An outdoor-vented kitchen range hood exhausting at least 100 cfm, or a continuous or intermittent fan providing five kitchen air changes per hour.
A bathroom fan removing at least 50 cfm or a continuously operating 20-cfm fan. Exhaust fans should be quiet so the noise doesn’t become annoying. The recommended rating is one sone (a measure of perceived loudness, as opposed to decibels, which are measured by machine ) for continuously operating fans and three sones for intermittently used fans. Also, buy energy-efficient fans. Combustion appliances like gas fireplaces or water heaters must meet code requirements. Air handlers or return ducts in an attached garage must be tested to meet airtightness specifications. Return-air vents must have good filters to remove contaminants that would otherwise be spread throughout the house by the air conditioning and heating system. Pleated filters with a MERV (minimum efficiency reporting value ) rating of 6 or higher are recommended.
To reduce indoor air pollution, the most effective methods are to control the sources and to improve ventilation.
In a typical 2, 000-squarefoot home with two bedrooms and two bathrooms, installing a kitchen fan and two bathroom fans that meet ASHRAE’s quality standards will cost anywhere from $ 1, 500 to $ 4, 000. The cost depends on numerous factors such as style of the range hood and fans, length of ducts and electrical work required.
While efficient air cleaners with high flow rate can reduce those particle-type pollutants, even the best run third to source control and ventilation to improve indoor air quality, says the federal Environmental Protection Agency.
The ideal time to create a structure with good air quality is while it’s being built. Installation of basic kitchen and bath fans averages $ 200 at that point.
Incorporating a whole-house balanced ventilation system will cost more and depend on the size of the house. Other choices can reduce contaminants, too (also when remodeling ) such as using formaldehyde-free building materials and furnishings. Coming next week: Protect yourself against the elements — natural and otherwise — with suitable home insurance.
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