One of the benefits of building a super-tight, well-insulated house is that you can downsize the HVAC system. Our strategy for the Model ReModel (an annual project covered by ProRemodeler) was to use three mini-splits from Fujitsu: a 12,000 BTU wall-mount unit for the main part of the house; a 7,000 BTU wall-mount unit for the master bedroom area; and a 7,000 BTU slim-duct unit for the bathroom/laundry. And because the house is tightly air sealed, we added mechanical ventilation to ensure a supply of fresh air.
When it comes to ventilation systems, you have four options: supply-only, exhaust-only, balanced, and balanced with energy recovery. We’re using a balanced system, meaning fans will push and pull air into and out of the house in equal amounts. We’re not using energy recovery because in a house of this size (about 1,250 square feet), the energy penalty is so minimal that it doesn’t justify the added cost of an energy recovery ventilator.
Two ducts make up the heart of our system. One carries fresh air pulled in by a filtered Air King Q-Fresh fan in the crawl space that modulates flow based on temperature and humidity of the incoming air. A second duct carries the air into a distribution box located under the attic insulation that splits the flow into several branches. The fresh air picks up some heat as it flows through ducts in the conditioned space, but most is still dumped into closets to avoid drafts and keep the house feeling comfortable.
We also have an Air King range hood that not only functions as an exhaust for cooking operations, but is synchronized to the supply fan. The range hood runs continuously to draw air out of the house, which is simultaneously replaced by the supply fan. This system follows code and exchanges air at the rate of 70 CFM, but it can be adjusted up or down.
Finally, in the bathroom we’re using an Air King EcoExhaust vent fan above the shower. It runs on a manually set timer, but is also connected to a humidistat that will automatically exhaust moist air out the gable end.