Minneapolis Passive House: The Home That Makes Money

1. No Natural Gas

This is essential for our society’s transformation to a clean energy economy, commonly called electrification. That means no gas heater, no gas stove, no gas fireplace. How? The technology exists: induction stoves are leaps and bounds better than the old electric stoves that were hard to clean and hard to control the heat level. Electric heat pumps to cool and heat the house have become much more efficient. Hot water is heated with an AO Smith air-to-water heat pump. The benefit of no natural gas is threefold:

• Better indoor air quality and a healthier home. First, no fossil fuel burning in the home means no carbon monoxide, nitrous oxides, volatile organic compounds, or other harmful emissions that can detrimental to your health—including no greenhouse gas emissions, which contribute to global climate change. 
• Energy efficiency. Second, no combustion means no fumes to vent outside, eliminating the need for additional holes in the home (which would lead to a leakier house).
• Safety. In previous homes, the Johnsons were aware of three different natural gas explosions in neighboring homes, and they frankly just wanted to make the safer choice. When you think about it, it’s a little crazy how most of us do not ever think about the highly combustible gas lines running underneath our yards and into our homes!

2. It’s All About the Building Envelope

The central tenet of a passive house is its windows’ orientation toward the sun in order to take advantage of the sun’s free heat in the winter while having shading on that side in the summer to keep it cool. The home needs to keep that heat inside, which means the walls, windows and doors have to be super well insulated—and where they come together must be tightly sealed so there are no air leaks. The Johnson’s home accomplishes this through insulated concrete forms (ICF)—8 inches of concrete plus foam insulation + stucco = 24-inch walls. They chose German-made Muller Schreinerei triple-pane windows—aluminum on the outside and wood on the inside—rated for Passive Haus, with an astonishingly low U factor (which measures a window’s resistance to heat flow). Opening and closing the windows and doors is like opening and closing a safe. It is so airtight that their blower door test came back with 0.35 air changes per hour (ACH) at 50 Pascals pressure. For context, building code in Minnesota was recently lowered from 5 ACH to 3 ACH (at 50 Pascals); LEED Homes v4 will give you two points for a blower door test that comes back at 2.0 ACH or less. Now that is a tight building envelope!