Passive House Ventilation vs Trickle Vents: Why MVHR is Healthier, Warmer & Mould-Free
Whenever we visit our Baltic partners, one topic always bubbles up over coffee:
Why isn’t Passive House a standard practise in the UK?
With more than half of the EU embracing this building method over the past two decades (the ones who have our climate). Yet in the UK, adoption has been painfully slow.
Why? It usually comes down to the same debate: mould and ventilation.
Here, many still believe the only way to avoid damp is with trickle vents, drop-out vents, or a little “natural draft.” But that thinking ignores what our neighbours already know: you can have healthier homes, lower energy bills, and fresh, filtered air without sacrificing comfort.
So, how about you join our coffee break chat to explore:
What a Passive House is and how it works
Why mechanical ventilation is EVERYTHING in this system
How it tackles mould without wasting energy
And why UK construction often misunderstands this approach
Let’s dive in.
Panelised Home From THC Homes
The UK Approach: Trickle Vents & Drafts
For decades, UK homes have relied on natural ventilation — leaving the building fabric a bit leaky, or adding trickle vents in windows to let “just enough” fresh air seep in. Kitchens and bathrooms often get intermittent extractor fans, while the rest of the home is expected to “breathe” through gaps.
The theory: fresh air in through the vents, stale air out through extractor fans.
The reality:
Airflow is unpredictable — too much on windy days, too little on still ones.
Cold outside air dumps straight into the room, creating drafts.
Occupants often close vents because of noise, cold, or aesthetics.
Moisture isn’t removed where it matters most, leading to persistent mould risks.
It’s easy to see why some experienced UK builders say: “The tighter you build, the more mould you’ll get — unless you add more vents.”
The Passive House Approach: MVHR
Passive House (or Passivhaus) flips this thinking on its head. Instead of uncontrolled leakage, it uses Mechanical Ventilation with Heat Recovery (MVHR):
Fresh, filtered air is supplied continuously to bedrooms and living areas.
Stale, humid air is extracted continuously from kitchens, bathrooms, and utilities.
A heat exchanger transfers 80–95% of the warmth from the outgoing air to the incoming air.
The result is a system that works like lungs: fresh air in, stale air out, all controlled and balanced.
Why “Better Builds = More Mould” Is a Myth
This belief comes from real experience: builders have seen tightly sealed extensions or double-glazed homes develop condensation and mould. But that’s because the airtightness improved without a ventilation strategy.
Passive House pairs airtightness with MVHR. That means:
Moisture is extracted at the source (showers, cooking, washing).
Humidity levels stay balanced across the home.
Surfaces stay warm and dry — no cold corners where mould can take hold.
It isn’t airtightness that causes mould. It’s airtightness without proper ventilation.
Why This Matters for Health
You breathe about 11,000 litres of air a day — so quality matters.
In a study of 648 Passive House homes, 74% never exceeded 1,400 ppm CO₂ indoors — a level where poor sleep and drowsiness often begin in conventional UK homes【passivehouseaccelerator.com】.
Filters remove pollen, dust, and outdoor pollutants.
Consistent humidity levels mean less mould, fewer allergens, and cleaner lungs.
It’s the difference between waking up groggy in a stuffy room… or refreshed in a space filled with clean, oxygen-rich air.
Why It Matters for Bills
Ventilation can account for up to 30% of a home’s heat loss if it’s uncontrolled【paulheatrecovery.co.uk】.
With MVHR:
Up to 95% of warmth is recycled【admsystems.co.uk】.
Heating demand can drop from ~35 kWh/m² in a typical UK house to ~15 kWh/m² in a Passive House【paulheatrecovery.co.uk】.
That’s serious money saved — and far more stable comfort.
Fun Analogies to Picture It
The Balloon vs. the Lung
UK homes = balloon full of holes: always losing air and needing reheating.
Passive House = lungs: one way in, one way out, always controlled.
The Tea Mug
Lid off = UK home without MVHR: steam (heat) disappears fast.
Lid on with controlled spout = Passive House: warmth stays in, balance maintained.
Myths Busted
“Trickle vents stop mould.” - Not reliably. Many vented homes still suffer damp. MVHR removes moisture continuously where it matters.
“MVHR wastes electricity.” - Fans run at about the same power as a lightbulb, but recycle most of your heating. Net result = lower bills.
“It’s too complex.” - Modern systems are quiet, efficient, and need only simple filter changes a few times a year.
Why We Use Passive Principles in All Our Models
We moved our UK factory from Straford-upon-Avon to the Baltics over three years ago and havn’t looked back! From healthier building materials, low carbon construction and a better space for the end user that is highly energy efficient, has cleaner indoor air and a sense of calm from the natural materials. To us it was a no brainer to build Passive House principled homes
Because:
Health first: fresh, filtered air 24/7
No mould, no damp: humidity controlled at the source
Low running costs: warmth stays inside where it belongs
Future-proof: regulations are tightening, energy prices are rising — Passive House is already the answer
Conclusion: Stop Leaking, Start Breathing
For too long, UK homes have put up with drafts, damp corners, and sky-high bills. Meanwhile, much of Europe has proven there’s a better way.
Passive House ventilation isn’t about sealing people into boxes — it’s about giving homes lungs: controlled, clean, efficient breathing that keeps you warm, healthy, and comfortable.
For more information on Passive House Principles Homes, visit our blog page for expert advice!
