Fun with Ventilation

There has been a flurry of activity out at the house recently. We installed two new Panasonic bath exhaust fans and a whole house Panasonic Energy Recovery Ventilator (ERV), all three of which were generously donated by Panasonic. Bath and kitchen exhaust fans are essential in ensuring good indoor air quality by removing pollutants from the home. They are also Energy Star certified, so they will be both energy efficient and quiet.

Bath exhaust fans rarely provide the amount of airflow that they are rated for due to poor duct installation. Installing small exhaust ducts with lots of elbows and long runs seriously restricts the airflow, but they are very common mistakes. Instead, the duct should provide a short and direct route outside of the house, and the ductwork should be pulled tight. As though they were trying to prove my point, I had to ask the electricians to rotate both of the bath exhaust fans because the initial installation positioned the exhaust port much too close to the ceiling joist, leaving no place for the duct to connect and run to the exterior. Once they were corrected and facing the right way, we used a combination of hard metal piping and flex duct (see photo below). We’ll do airflow testing at the final to verify the exhaust fans are providing the rated performance.

Figure 1. Correctly installed bath exhaust

We’re trying to make the Green on Gift home as airtight as possible while also providing good indoor air quality. There is a common misconception that “houses need to breathe.” In reality, houses should be as tight as possible. Occupants, however, do need to breathe fresh air, which should be brought into a tight house from outside through controlled mechanical ventilation instead of through leaks to the crawlspace, attic, garage, or outside. The Panasonic ERV filters and preconditions the incoming air stream. As it exhausts stale air from inside the house, it passes through a central core that transfers a portion of the heat to or from the incoming air stream, depending on the season. This moderates the temperature and humidity in the incoming air, keeping hot, humid air out in the summer and cold, dry air out during the winter. It also filters all the incoming air to keep out pollen, dirt, and other pollutants.

Figure 2. Correctly installed ERV with insulated ductwork.

We also decided to insulate the ERV ducts even though they will be with conditioned space (image above). This is a little “belt and suspenders,” but I’d rather not have any condensation in my conditioned attic. When I finally move in, my bathrooms and kitchens will have high quality exhaust systems that will remove the excess moisture and pollutants produced from showering and cooking, and the ERV will make sure that all the air inside is healthy and comfortable throughout the year.