A house is only efficient if it's healthy. According to the EPA, most of us don't meet that standard, as indoor air quality makes the top-five list of environmental health problems Americans face. The problem starts with moisture and contaminants. Excess humidity (caused by normal daily activities like cooking and showering) can lead to mold and even house decay, while contaminants and allergens found throughout the house in building materials or household appliances can lead to significant health problems. In other words, every day problems can get big and ugly. But we knew that. Fortunately, straight-forward air-sealing and ventilation solutions go a long way toward fixing those problems.
II. The Basics of Ventilation - how it works in your house (or doesn't).
Unfortunately for those of us who live in houses that whistle during wind storms, and whose mail slots flap when the dog barks, just because you can feel a draft doesn't mean your house is properly ventilated. In fact, there are three big problems with so called "natural ventilation."
1. Natural ventilation that occurs in a drafty house is often limited to those leaky areas, leaving the rest of the house full of stagnant, stale air.
2. Relying on natural ventilation alone provides no way to control the amount of moisture or contaminants that enter the house.
3. Most air leaks occur in the basement, which tends to be a moisture rich breeding ground for mold, a common household menace that we can help you live without.
For all of these reasons, it is necessary to take an active role in determining how your house exchanges air with the world.
III. Take this on: Seal up your house, then make it breathe!
We recommend this two step approach.
1. Seal up your house. Moisture is transmitted in a variety of ways, and adequate ventilation alone won't keep every corner dry. Ideally, a home will have vapor barriers both on the outer walls and beneath the floor to minimize the transmission of moisture through capillary movement.(Meaning movement through porous materials; i.e. water seeping from the ground into the concrete foundation and from there into the framing) and diffusion (water molecules moving through a wall). Homes should be sealed properly to prevent unwanted moisture from sneaking in through cracks and crevices. As always, we recommend an energy audit to pinpoint less visible problems with your home's building envelope, but any visible leaks (around windows or doors, for example) you may as well take care of as soon as possible. To get a sense of the best tools for each job, check out our air-sealing buyers guide.
2. Manually/mechanically ventilate your house. Harmful contaminants hang around every house, airtight or not, including chemicals from building materials (particle board, glues, etc) and emissions from gas-burning appliances like stoves and furnaces. These can be effectively minimized with proper sealing, venting, and adequate air circulation from a mechanical ventilation system. The EPA recommends a rate of .35 air changes per hour (that is, just over 1/3 of the air in your home being replaced every hour; or 3 hours for a full air change), and no less than 15 cubic feet per minute [cfm] per person living in the house. A kitchen should have a fan that runs around 100 cfm intermittently or provide 5 air changes per hour continuously, and a bathroom fan should run at either 50 cfm intermittently or 20 cfm continuously. The key is to make sure that harmful air is being discharged outside, and that fresh air is being circulated throughout the entire home and not just in targeted areas.