How a Passive House Stays Cool in Summer and Warm in Winter (with Lower Utility Bills)

Keeping Cool in Summer

If you go into a typical home when the outdoor temperature is up in the 90s or has even reached triple digits, you’re likely to hear the incessant whirring of the air conditioner as you feel the blast of cold air that it pushes through the ducts. During a recent interview, Nic Zweifel, owner of a Kala high-performance home, recalled his exasperating experience in a brand-new Kansas City loft that he’d assumed would be much more efficient than it actually was. 

“It just wasn’t comfortable,” he said. “The air conditioner was on full blast all the time because no matter what temperature we wanted it, it had to work hard to keep it there, so there was always background noise.”

When you step inside a Passive House in July or August, you might be surprised not to hear much of anything. That’s because it doesn’t require a regular air conditioner constantly gulping energy and running on full blast to bring the indoor temperature down. Thick insulation keeps cool air within the walls, as there aren’t the usual gaps in the building envelope for it to leak out of. 

An ERV unit runs quietly in the background, constantly bringing fresh air in through an advanced filtration process and circulating it throughout every area of the home. Intentional shading of well-placed windows helps ensure that while windows provide a connection to the natural environment outside – and contrary to a common misconception about Passive House construction, can be opened to welcome a breeze on cooler days – they don’t let too much heat energy in during the summer months. 

In an interview, Morgen Govindan, another Kala homeowner, described how a tight building envelope with an air barrier, the ERV system, and high-performance windows and doors help eliminate the temperature swings she was used to in previous houses and provides increased comfort. “There’s very little variability when you walk up or downstairs,” she said. “In the summer, it makes a big difference that it’s not significantly hotter upstairs. It’s just consistent throughout.”

Staying Warm in Winter

In a recent interview, one of the owners of the first Phius-certified Passive House in Missouri described how a combination of continuous, plentiful insulation, thick walls, and an efficient heat pump keeps warmth in and cold out during even the coldest Kansas City weather. 

“It can be the dead of winter and I’ll walk around in shorts and a t-shirt and be totally fine and comfortable,” Pooja said. 

She can vividly recall the temperature regulation issues that many houses she has been in have experienced: “If it's a cold winter day and I'm sitting next to a window, I can feel the draft and the frigid temperature from the window and I’m not even in contact with it.” There are several reasons for this. First, the glass itself in many traditionally built homes is low quality and allows too much heat energy to escape during cold weather. Second, such windows are often framed with materials that conduct further warmth out and away from the inside of a house. And third, poor installation can allow drafts to breeze in unbidden. 

In contrast, the glass in a high-performance home does not allow heat loss from around its edges. Gas between two or more panes also has an insulating effect. Thoughtful framing utilizing materials with low heat conductivity helps retain even more warmth in winter. And an expert team of installers ensures that windows are put into walls tightly and sealed and flashed adequately. 

Another way that windows in a Passive House help to keep heat inside the home is that the structure itself is oriented properly on the best part of the building site and facing the right direction. This typically involves having plenty of south-facing windows to capture passive solar energy from the sun in winter, considering its path across the sky from sunrise to sunset. Welcoming nature’s warmth in this way further reduces the burden on the mechanical system to compensate for seasonal temperature fluctuations. 

To provide added heat when needed, a Passive House uses a heat pump. Instead of relying on the burning of natural gas like most homes, this sources warmth from the air and/or ground to make subtle adjustments to the interior environment without running on overdrive to keep up. Heat from the air that’s continually being exhausted flows through a heat exchanger in an ERV system, providing up to 90 percent heat recovery. As a result of this efficient process, homeowners are insulated from the rapidly rising utility costs that have hit people hard in the past few years. 

Such advanced heating and cooling technology helps Passive House owners save several hundred dollars per month and reduce energy usage by 80 to 90 percent, particularly in peak seasons when HVAC systems are usually working overtime. They do so without the need for the constant manual adjustments that become routine in a regular house. 

“The feedback that we get from guests is that it’s very quiet and comfortable,” Sush Govindan added. “We’ve hardly had to adjust the thermostat at all – I’ve only touched it three times.”