Some existing homes may already be too tight to assure safe air quality or to offer additional energy savings. Homes that were sealed in the past, without today's air tightness detection technology, may have been sealed to a point below minimum standards. These homes may require mechanical ventilation and do not need to be sealed further. The recommended way to know if a home is already tight is to have a blower door test conducted to measure air exchanges in the home. Blower door tests are conducted by trained weatherization professionals.
For most older homes, it is unlikely that weatherization will make a home too tight. A study on this topic was commissioned by a large utility company, concerned about this issue in relation to its own weatherization program. Researchers at Lawrence Berkeley labs concluded that aggressive weatherization reduced airflows in homes by about 30%. Traditional home construction, in all but the coldest climates, has not focused too much attention on tight construction, especially in older homes. More recently, more attention is being given to build tight and ventilate right.
However, in homes that use combustion appliances (e.g. gas ranges, furnaces, water heaters) it is important to be cautious when sealing homes. Combustion appliances require adequate oxygen to perform efficiently and safely. In many locations, for new construction and if the house is weatherized, local codes require that the combustion air comes from the outside through properly sized and located intake ducting.
In colder moist climates, one indicator of excessive ventilation is a too-dry home during the heating season. This is evidenced by signs of static electricity: tiny shocks when touching conductive objects, clinging clothes, and occupant complaints of dryness. Cold drafts along baseboards and electrical cover plates (outlets and switches) on exterior walls are another of excess air leakage. Such homes will benefit from weatherization. On the other hand, homes that are too tight may show signs such as cooking odors that linger for many hours, and condensation on windows even at moderate low temperatures. The latter might also indicate excessive moisture levels.
A home that has excessive production of pollutants or moisture may be on the brink of an indoor environmental problem, saved only by excessive air leakage. In such homes, aggressive weatherization may bring these issues to the forefront, ‘creating’ an indoor pollution problem.
Have the house tested using a blower door test to determine if there are adequate or excessive air exchange rates.
