We just put new windows in our house and paid to have more insulation in the attic and weatherstripping around the doors. The house seems very tight now (less drafts, more comfortable). Someone mentioned to us that we now need some mechanical vents to control air flow. Any idea on what this is?
Mechanical ventilation is an important, and often forgotten, last step when weatherizing an older home or building a new house. When a structure is sealed tight for energy efficiency reasons, the unintended consequences can often be stale indoor air and moisture that have no way to escape.
This problem can be eliminated by using correctly sized and installed exhaust fans in all the bathrooms in your home, as well as a high volume hood in the kitchen. You should inspect each exhaust fan in your home and make sure that it is properly vented to the outside, usually by way of a sealed duct and a louvered vent. (Be aware of incorrectly vented fans that discharge the air into an attic, crawlspace, or soffet space.)
Of course getting stale air and moisture out of your house is only half the battle. You may also need to install a heat recovery ventilation (HRV) system that actually brings fresh outside air into your home's interior. An HRV system is designed to capture heat from the air that is being pulled out of your house and uses it to warm the fresh air that is being brought in from the outside. The end result is an efficient system that helps to circulate fresh air throughout your entire house, while minimizing the loss of heat in the process.
Most HRV systems operate with a timer and rely on the existing duct-work in your home to distribute the fresh air. You should consult a HVAC contractor to see what size unit would be right for your home and to get an estimate on the cost of installation. Although this type of home improvement can cost between $4,000-$7,000, an HRV system is the most effective way to combat stale indoor air and to maintain a healthy environment inside your home.