Window-mounted HRV
Lloyd Alter
Josh raised a very important point in his post What You Need to Know About Caulking and Health: you need adequate ventilation in your home. But if you caulk it and seal it and tighten up its envelope like every green site on the web says, you can run into serious problems. Humidity can build up and cause mold and rot; toxins can build up, including formaldehyde, radon and toxins from cleaners and even air fresheners.
And with more homes depending on air conditioning, the need for fresh air continues all year round.
Old houses were naturally ventilated; they leak like sieves. Furnaces and exhaust fans create negative pressure and suck air through window frames or right through the wall. The air can change as often as three times per hour. A well-sealed new home designed to Energy Star standards can have as few as half a change per hour. But Alan Berman, in the Healthy Home Handbook, suggests that bedrooms need about 1.3 changes per hour, bathrooms and kitchens six, and is there a smoker in the house? Ten changes per hour.
So there is an inherent contradiction-the greener the home is from an energy point of view, the worse it is from an air quality point of view. That is why it is so important to use building materials that don't outgas, to avoid cheap particleboard or other materials that give off formaldehyde, to use green cleaning supplies, and if your windows are closed for most of the year, to install a heat recovery ventilator.
These devices are essentially two ducts that cross over each other through a labyrinth of metal, so that heat energy is transferred from the exhausted air to the incoming air (or vice versa if you are running this during air conditioning season) It recovers about 85% of the energy so you can bring in fresh air and warm it without significant fuel cost. In some countries (like Canada) they are mandatory; for some reason in the United States they are not, even in Energy Star rated homes.
But no green home should be without one.
