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Passion for Passive Housing


We all know the jokes about Colorado’s abrupt weather shifts. Monday brings warm sunshine and tank tops, followed by Tuesday’s snowfall and road closings. This natural madness is reflected perfectly in our monthly energy bills. What else can you expect when you leave your windows open on Monday night, then fire up your furnace on Tuesday? Thankfully, the unpredictable—and sometimes costly—nature of our weather can be nearly circumvented by a passive house.

A passive house is one that requires very little energy to sustain a comfortable inner environment. With traditional houses, homeowners lose a lot of energy from small holes and leaks. But the super insulated walls of passive houses keep energy—and costs—low.

Brian Fuentes, a certified Passive House Architect and the name behind Fuentes Design, filled us in on the finer points of passive housing. “Passive houses are more insulated, about ten times more airtight than your typical home in Boulder,” said Fuentes. “It leaks less air, which means that it’s more comfortable for the occupants. There’s also less chance of moisture damage from leaking areas.”

And, what of those energy savings?

“The annual heat demand is usually about ten times less. Annually, what you’re spending on heating and cooling will be much less than you’re used to. It saves you money in the long run,” said Fuentes.

The house is a near perfect energy trap that brings in external heat from the sun via passive solar gains, and uses that sunlight to maintain comfort. Fuentes went on to describe the process: “You gain energy from the sun by bringing it in through the glass and direct radiation into the building—the building then stores that energy.”

Thick windows also play a large role in this conservation and are the only building materials that need to be imported from outside of the United States. Beyond the thickness, the secret to their green power prowess is a tight seal.

“They’re massive windows that are triple paned and the frames are four inches thick, versus north American windows that are typically two inches thick,” said Fuentes.
But a super-insulated building is rendered useless without strategic building placement to prevent massive heat swings. Too much exposure to the sun during the summer would make the house hot, while not enough exposure in the winter would drop the temperature to very uncomfortable levels. That’s why new passive houses are designed with the majority of the windows facing south. The sun can provide about fifty percent of the heat needed to warm a house to a comfortable temperature.

Passive houses then rely heavily on internal heat gains.

“Internal gains are energy waste made by lights and people using equipment,” Fuentes said. “As people, we make about 100 watts of waste heat just by standing around.”

A well designed passive house can absorb and utilize internal gains so that the wattage generated by humans and appliances totals around fifteen percent of the total energy needed to heat the home. But how is all of the solar heat and human warmth recycled from the house? How does it cool down in the summer time? The answer is the heat recovery ventilation system, a small metal box responsible for ridding the house of unwanted warmth and stale air.

The ventilator recycles energy by collecting the heat going out of the house and reusing it to heat the incoming fresh air. In the summer, the ventilator works in reverse and reroutes incoming hot air straight into the exhaust of the home. Such a design means you don’t ever rely on air conditioning or heating units.

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