Ventilation Choices: Three Ways to Keep Indoor Air Fresh
Every House Needs Fresh Air
Delivering the right amount of fresh air
All the effort that goes into creating tighter houses results in significant energy savings and greater comfort. But moisture, chemical toxins, and cooking odors can’t dissipate as easily in a house with a tight envelope as in a leaky house. Opening a few windows may provide too much or too little ventilation, with adverse effects on comfort in either case. Even in houses where building materials and furnishings have been carefully chosen to reduce indoor air pollutants, some form of mechanical ventilation is a prerequisite for healthy occupants and a healthy building.
There are two basic strategies to provide mechanical ventilation: spot ventilation, which removes moisture and pollutants at their source, and whole-house ventilation.
Typical spot ventilation strategies include the use of bathroom exhaust fans and an exhaust fan over the kitchen range. Exhaust fans are available in a variety of sizes, styles and price ranges. Control options range from simple wall switches to sophisticated timers, occupancy sensors, or humidistats.
Whole-house mechanical ventilation systems are designed to remove stale air from or supply fresh air to the building as a whole. These systems are more complicated and more expensive than spot ventilation systems, but also more effective.
Use a variable speed furnace fan
Some ventilation systems use the furnace fan to distribute air around the house. In these systems, the fan speed used for heating and cooling is probably too high in a ventilation-only mode. A variable-speed or two-speed fan is more efficient, using less power for ventilation than for heating and cooling.
MORE ABOUT VENTILATION
Air sealing makes a house healthier
In designing any ventilation system, a few rules of thumb apply:
Building materials and furnishings that emit the least amounts of pollutants should be a first choice.
The most efficient ducts are smooth, straight, sized correctly, and sealed tightly. Corrugated ducts have greater resistance to airflow, and elbows and long runs of duct also reduce efficiency. Duct joints should be sealed with mastic. Ventilation ducts that pass through unconditioned spaces should be insulated.
Exhaust ducts should always be vented to the outside, not into crawl spaces, basements, or attics.
Don't forget about radon
Radon, a naturally occurring radioactive gas, is the second leading cause of lung cancer in the U.S., accounting for between 15,000 and 22,000 deaths a year, according to the National Cancer Institute. Radon can migrate through the soil and into basements, or enter a building via well water. Some parts of the country are at greater risk than others, but all houses should be tested for it.
Particularly in high-risk areas, a vent system designed to pick up radon from beneath the basement slab should be installed during construction. If tests later show radon levels are too high, it's relatively simple to install a fan and exhaust the gas before it can do any harm. Putting in a radon mitigation system after the fact is that much more difficult.
Designing a Ventilation System
For an in-depth discussion of this topic, see "Designing a Good Ventilation System."
Review of Residential Ventilation Technologies
RadonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles.
All About Radon
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