Indoor Air Quality
Indoor Air Quality refers to the quality of the atmosphere in a building. It encompasses many aspects of a healthy and comfortable atmosphere: temperature, humidity, and the amount of pollutants such as carbon dioxide, radon, volatile organic compounds and particulate matter. IAQ receives more attention these days because houses are more airtight and better insulated than ever before. While this means that houses use less energy, it also means that passive air leakage through the building envelope will not provide sufficient ventilation to moderate concentrations of airborne pollutants.
A huge number of Alaska homes -- an estimated 58% -- are airtight and lack continuous ventilation, putting them at risk of poor indoor air quailty (See the 2014 Alaska Housing Assessment for more detail.)
Temperature and humidity are primary measures of indoor air quality. The temperature of a home is usually regulated by the heating system. Water vapor, on the other hand, is produced by daily activities such as breathing, cooking, showering as well as houseplants and soils in crawlspaces. It is measured as relative humidity. Some humidity is desirable (30-40 percent is recommended) because it keeps skin and sinuses from becoming too dry, stops static build-up and is beneficial for people with asthma. High humidity, however, can cause problems for the house and its occupants. Humidity levels above 40 percent in winter in our climate can lead to condensation within the building envelope, which promotes the growth of mold, mildew and rot. Humidity above 60% any time of the year provides growing conditions for bacteria, viruses and fungi.
Pollutants are introduced into a house in many ways. Carbon dioxide is produced when people breathe, and is often used to gauge the indoor air "freshness" (the air exchange rate). Carbon monoxide is a dangerous gas produced by combustion heating appliances, gas ranges and cars. All homes should have a CO alarm near any bedrooms. Formaldehyde, which can cause long-term health problems, can be released from furnishings such as carpeting and cabinets. Radon is released from certain types of soils underneath a home’s foundation. Smoking, cooking and chemicals used for cleaning or pest control can also release pollutants into the home, triggering asthma symptoms, eye irritation, headaches or fatigue. Long-term exposure to some pollutants in sufficient concentrations can contribute to an elevated risk of cancer or respiratory disease. So -- it is important to manage pollutant levels within the home!
How is Indoor Air Quality improved in homes?
There are several ways to manage IAQ, and one of the most important is through ventilation. There are two basic types of ventilation: whole-house ventilation and local ventilation.
Local ventilation is used in high-pollution areas, such as kitchens and bathrooms. The purpose of local ventilation is to remove humidity and pollutants before they migrate to other areas of the house. This is typically achieved using exhaust ventilation, such as range hoods and bath fans. These devices can be controlled by switches or run on a timer and serve to exhaust pollutants and excess humidity.
There are many ways to provide whole-house ventilation. The first relies on natural air leakage, a strategy that was common in the past when homes were not built as tightly as they are today. With no mechanical ventilation system, natural pressure gradients caused by wind and temperature differences move air through open windows or the building envelope. This strategy is not recommended for either leaky or tight homes. In an old leaky house, you are wasting energy as heat escapes through the walls, windows and roof. In a tight home, natural air leakage is unreliable and often insufficient.
Two whole-house mechanical ventilation strategies are exhaust-only and supply-only systems. An exhaust-only system usually consists of one or more bathroom fans designed to run continuously. Fresh air must enter through the building envelope. In a supply-only system, a central fan is typically integrated into a forced air distribution system and brings fresh air into a home. Supply-only systems are not recommended in Alaska since they force moisture from inside the house into the building envelope.
The final, and best, whole-house ventilation strategy is a balanced, distributed system such as a heat recovery ventilator (HRV) or an energy recovery ventilator (ERV). These appliances exhaust stale air and provide fresh air at an equal rate, distributing it through the home through a ducted system.
No matter what the strategy is for a ventilation system, make sure it’s working properly and that outdoor air vents are open and unblocked.