For centuries homes weren’t ventilated, and they did all right, didn’t they? Why do we need to go to all this effort (and often considerable expense) to ventilate houses today?
Engineers have developed several reasons that ventilation is more important today than it was long ago. Most importantly, houses 100 years ago were leaky. Usually they didn’t have insulation in the walls, so fresh air could easily enter through all the gaps, cracks, and holes in the building envelope., the building materials used 100 years ago were mostly natural products that didn’t result in significant off gassing of volatile organic compounds (VOCs), formaldehyde, flame retardants, and other chemicals that are so prevalent in today’s building materials, furnishings, and other stuff.
All Homes Should Have Mechanical Ventilation. With better-insulated, tighter homes that ventilation is even more important. But even in a very leaky house, one can’t count on bringing in much fresh air or calm days in the spring and fall when there isn’t a pressure differential across the building envelope. (See above Figure) If budgets allow, going with balanced ventilation is strongly recommended, and if you’re doing that in a relatively cold climate, like ours, then providing heat recovery is a no-brainer. Mechanical ventilation always takes energy; with heat recovery, the energy penalty of fresh air is minimized. ( Ventilation Options)
Exhaust-only Mechanical Ventilation. This is a relatively common strategy in which small exhaust fans, usually in bathrooms, operate either continuously or intermittently to exhaust stale air and moisture generated in those rooms. This strategy creates a modest negative pressure in the house, and that pulls in fresh air either through cracks and other air-leakage sites or through strategically placed intentional make-up air inlets. An advantage of this strategy is simplicity and low cost. A disadvantage is that the negative pressure can pull in radon and other soil gases that we don’t want in houses.
Supply-only Mechanical As the name implies, a fan brings in fresh air, and stale air escapes through cracks and air-leakage sites in the house. The air supply may be delivered to one location, dispersed through ducts, or supplied to the ducted distribution system of a forced-air heating system for dispersal. A supply-only ventilation system pressurizes a house, which can be a good thing in keeping radon and other contaminants from entering the house, but it risks forcing moisture-laden air into wall and ceiling cavities where condensation and moisture problems can occur. (Home Insulation)
Balanced Ventilation. Much better ventilation is provided through a balanced system in which separate fans drive both inlet and exhaust airflow. This allows us to control where the fresh air comes from, where that fresh air is delivered, and from where exhaust air is drawn. Balanced ventilation systems can be either point-source or ducted. With ducted systems, it makes sense to deliver fresh air to spaces that are most lived in (living room, bedrooms, etc.) and exhaust indoor air from places where moisture or pollutants are generated (bathrooms, kitchen, hobby room).
Balanced Ventilation with Heat Recovery. If there are separate fans to introduce fresh air and exhaust indoor air, it makes a lot of sense to locate these fans together and include an air-to-air heat exchangers o that the outgoing house air will precondition the incoming outdoor air. This air-to-air heat exchanger—more commonly referred to today as a heat-recovery ventilator or HRV—is the way to go in colder climates. A slightly different version, known as an energy-recovery ventilator (ERV), is similar but transfers moisture as well as heat from one airstream to the other, keeping more of the desirable humidity in the house in the winter and reducing the amount of humidity introduced from outdoors in the summer.(Ventilation Options )
Glew Engineering can help with your Ventilation needs throughout your home. Glew Engineering has novel up to date ideas on ways to solve your problems and get the best value on projects for your home.