Can I Still Open the Windows in an Airtight Passivhaus?

In the UK, many of us live in homes that simply aren’t comfortable — often cold, draughty, damp and prone to mould, with poor indoor air quality.

We’ve become so used to cold, leaky homes that we often don’t think about the discomfort they cause. We just turn up the heat, consume more energy and drive up our bills further.

But the reality is, these issues aren't just inconvenient—they’re harmful to our health.

Cold homes raise blood pressure, while mould increases the chance of depression and can even be fatal in severe cases. Poor indoor air quality worsens conditions like asthma, allergies and eczema and can contribute to lung cancer.

Given that we now spend nearly 90% of our time indoors, it’s crucial that our homes support our health and wellbeing.

Passivhaus is most well known as "the world's leading standard in energy efficient construction". 

But many people don’t realise that Passivhaus is also a strict comfort standard, ensuring homes are free from draughts, cold spots, condensation and overheating, while maintaining a comfortable temperature and excellent indoor air quality all year round.

This may sound like magic, but it’s the result of the meticulous way a Passivhaus is designed and built, with airtightness (one of the five principles of Passivhaus design) playing a key role.

Airtight construction means there are no gaps in the building for air to leak in or out. So your Passivhaus is completely draught-free. This is achieved through the use of a continuous air barrier that envelopes the entire building – from the walls and roof, to the floors and openings. The design process identifies all potential air leakage paths, which often occur at the junctions where two building elements meet, such as:

— Where walls meets the roof
— Where walls and floors meet
— Where walls and windows meet
— Where building services such as pipes, cables, electrical outlets or ducts pass through the air barrier

During construction, even the smallest of these gaps are sealed using specialist tapes and adhesives. Anywhere an air leak could occur, Passivhaus makes the extra effort to plug it, stopping cold air blowing in and warm air escaping.

For a home to be certified as a Passivhaus, it must meet a strict airtightness target, far more demanding than typical homes.

This is verified through an airtightness test, also known as a blower door test, which measures how much air leaks out of the home when placed under controlled pressure.

Your Passivhaus will have two such tests—one during construction and another after completion—to ensure it satisfies the criteria.

An airtight Passivahus can create the impression of an unpleasant, stuffy home — but that’s definitely not the case.

A Passivhaus uses a Mechanical Ventilation with Heat Recovery system (MVHR), which acts like the home’s lungs, simultaneously extracting stale air and delivering fresh, filtered air 24/7.

Here’s how it works:

The MVHR system monitors for healthy temperature and humidity levels around the Passivhaus to make sure that the rooms aren’t too humid or dry. The temperature is normally set at 20 degrees in a Passsivhaus, as it’s considered the optimal temperature for human comfort.

The best thing about an MVHR system is that its filters remove dust, pollen and pollutants from the incoming air, helping reduce triggers for hay fever, asthma and eczema and improving the health of occupants.

Careful checks on the design and the installation ensure the MVHR works effectively and that the intended air flow is actually delivered. The ventilation system is also whisper-quiet and must meet strict noise limits.

Yes, you can open windows and doors in a Passivhaus just like in any other home. But perhaps the question should be – why do we open windows at all?

We open windows to enjoy a breeze or birdsong, or for less pleasant reasons, like clearing out a steamy bathroom or burnt food smell. The amazing thing about living in a Passivhaus is that those less pleasant reasons mostly disappear.

Thanks to the MVHR system (constantly removing stale, moist air and supplying fresh, filtered and perfectly temperate air) bathrooms don’t steam up, cooking smells vanish, laundry dries faster and bedrooms stay fresh. You won’t need to open windows to defog the bathroom mirror or air out a stuffy bedroom, because these problems simply don’t occur.

If you need to quickly clear the air in a Passivhaus (ie - dinner burnt and smoke is filling the kitchen) – just turn up the MVHR fan for 30 seconds and the air is fresh again. It’s faster and easier than opening all the windows.

The MVHR system also means you can keep your windows closed if you want to block out traffic noise, pollution, pollen, or even countryside odours like manure.

While the Passivhaus model assumes you'll open windows for natural ventilation during warmer months, it’s less practical in winter, as letting in cold air will increase heating costs. However, most Passivhaus residents find they don’t need to open the windows as much, because the air quality and indoor environment remain consistently comfortable all year round.

Airtight construction is about creating a comfortable, energy-efficient home that doesn’t sacrifice fresh air or the option to open your windows. It’s not about sealing off your home from the outside world, but rather about optimising the way air moves in and out, ensuring a steady flow of fresh air and maintaining a healthy, comfortable temperature year-round.