In days past, when adding additional insulation became more feasible in construction; builders and contractors were not as savvy to the need or sizing of proper ventilation and circulation of air. Ventilation is exchanging indoor and outdoor air by opening a window, turning on a bathroom or stove-top fan that vents outdoors, using a forced air system and/or installing a HRV system.
Circulation is the movement of indoor air achieved by using a ceiling or other indoor fan. Circulation is not enough because as we cook, bath and even breathe we release moisture into the air as well as CO2. Our furniture, building material and household cleaners off-gas toxic chemicals and our stoves and heaters produce pollutants too.
In older homes, the exchange of indoor and outdoor air happens quite naturally because of the lack of insulation and air-sealing. Additionally as explained in my post R-Vaule It’s Not What You Think, I demonstrate that as the temperature outside becomes either warmer or cooler than the temperature inside, the flow and speed of air increases as they try to equalize each other out. So the warmer you set your thermostat in the winter, the faster you lose heat through tiny gaps in the wall.
In newer or renovated homes that offer better air-sealing and insulation value, we need to add additional ventilation to ensure that fresh outdoor air is being exchanged with indoor air that is moist and polluted. Read more about Indoor Air Pollution here.
Additionally, as we improve the barrier between the outside and inside, we increase the opportunity for condensation on interior walls, which can lead to unwanted mold. In an older home, as the thermostat is turned up, the warm air is literally sucked through the walls heating both the interior and exterior of the wall. In a newer or renovated home with high insulation and air-sealing installed, the interior wall is the same temperature as the thermostat while the exterior of the wall is cold. The warm inside air inside is holding moisture until it comes across the cold wall where it immediately condenses along the wall creating an ideal habitat for mold.
Newer homes will often come with a whole house fan installed on a timer. Builders will educate new home buyers on the frequency of how often the timer should be run. In homes with forced-air heating the system will pull fresh outdoor air in; as part of the heating process. In homes with electric baseboard, radiant or radiator style homes, there is minimal movement of air. In these homes, you may find windows that have very small openings to allow fresh air in or better yet the home will have a HRV (Heat Recovery Ventilation) system installed.
Of course opening windows or doors is the simplest solution, but when it’s cold outside and you want to only heat the air once, a HRV system gives you the best of both worlds. Fresh air that’s pre-heated by the old air as they pass by each other.
If you are looking for a home, and indoor air quality is tops on your list, click the link below and I can provide you a list of homes with a HRV system installed or I can help identify good home candidates where a HRV system can be added.