Trickle vents or heat recovery ventilation? A cost and benefit analysis of ventilation systems
After replacing old windows with modern, airtight units, a problem emerges that most homeowners don't anticipate. Condensation forming on the glass, mould in the corners of rooms, feeling groggy in the morning – these are signs that your home is literally suffocating. Modern windows with a U-value below 0.9 W/(m²K) provide excellent insulation, but without effective ventilation, your home becomes a moisture-laden thermos of stale air. You now face a choice between three solutions: micro-ventilation (an emergency function built into windows), trickle vents (dedicated devices for fresh air supply), or mechanical ventilation with heat recovery (MVHR). This article will help you make an informed decision based on your situation, budget, and current building regulations.
Building regulations and ventilation: How to avoid compliance issues
Modern building regulations increasingly limit primary energy consumption in new buildings. A natural ventilation system – trickle vents plus extract ducts – expels heated air to the outside without recovering any warmth. With a standard heating system such as a gas boiler, energy consumption often exceeds regulatory limits, which can cause problems during building inspection.
Heat recovery ventilation reduces energy demand by reclaiming 50–90% of heat from extracted air. This directly translates to lower primary energy consumption, making it easier to meet building standards. A home with MVHR requires neither ventilation chimneys nor window trickle vents – a saving that partially offsets the higher system cost.
According to established ventilation standards, a home requires specific minimum air extraction rates: a kitchen with a gas hob needs 70 m³/h, a bathroom 50 m³/h, and a living room 30 m³/h. A typical trickle vent allows 20–50 m³/h at 10 Pa pressure difference. To ensure adequate air exchange in a 120 m² home, you need a minimum of five to seven trickle vents – a fact often overlooked by homeowners.
Micro-ventilation – free solution or a fast track to heat loss and mould?
The micro-ventilation function – the handle in a 45-degree position – is an emergency ventilation feature intended only for brief use. Most manufacturers’ technical specifications recommend using it for no longer than 15–30 minutes. Why?
Micro-ventilation creates a linear gap of 5–10 mm around the entire perimeter of the window sash. Cold air flowing through this narrow gap chills the window rebates. When indoor humidity is high, water vapour condenses on the seals. On frosty days, the water freezes, damaging the EPDM gaskets – after one winter season, they lose their elasticity and no longer seal properly against the profiles.
Security consideration: A window in micro-ventilation mode is partially unsealed, which has implications for home insurance. The security rating (RC class) does not apply in this mode. Furthermore, micro-ventilation completely negates the window’s acoustic insulation – if you’ve invested in windows with a high sound reduction rating of Rw 40–45 dB, opening the sash gap allows street noise to enter almost as freely as through a tilted window.
Safe ventilation with windows closed? Discover MACO Secuair
A better solution is the special ventilation position available in MACO Multi-Matic hardware with the optional Secuair function. This system allows you to leave the window ajar whilst maintaining RC2 security rating. The minimal tilt opening provides energy-efficient, continuous ventilation even during extended absences. An additional handle position enables safe ventilation without concerns about seal damage or security.
Trickle vents in older homes: Solving moisture problems after window replacement
Trickle vents provide an effective solution for natural ventilation with airtight windows. Unlike micro-ventilation, they have a calibrated nozzle and flow-regulating mechanisms, making them a genuine component of the ventilation system. As buildings become increasingly airtight, natural air exchange barely occurs – contaminated air and accumulated moisture cannot escape to the outside.
Humidity-controlled, pressure-controlled, or rebate vents? An overview of vent types
Humidity-controlled vents are the most popular solution. They work on the principle of automatic response to humidity – inside is a polyamide strip that changes length depending on the relative humidity in the room. When humidity exceeds 70%, the damper opens fully, admitting more air. When humidity drops below 35%, the vent closes, reducing heat loss. They operate without electricity and require zero maintenance.
Pressure-controlled vents are designed for tall buildings and locations exposed to strong winds. The damper responds to the pressure difference between outside and inside. When strong wind hits the façade creating positive pressure, the damper blades automatically restrict the airflow aperture, maintaining constant airflow and protecting against draughts.
MACO VENT rebate vents are a special solution that remains hidden in the window rebate. They can be fitted to existing PVC windows with just two screws, without routing the profiles. MACO VENT automatically closes in excessively strong winds and pre-warms incoming air, minimising the sensation of cold draughts.
Noise and air quality: Do acoustic vents with filters provide effective protection?
A trickle vent is an opening in the window through which air flows – and therefore noise as well. The noise level of standard models is 30–40 dB, equivalent to a quiet conversation in the next room. You won’t notice this during the day, but at night when you want to sleep in silence, the airflow may be clearly audible, particularly in strong winds.
The solution is acoustic vents with additional sound attenuators. Their acoustic attenuation is 35–40 dB in the open position and up to 41 dB when closed, comparable to the parameters of the entire window – ideal for locations near busy roads.
Modern filters fitted in trickle vents capture up to 98% of PM10 particulate matter as well as a significant proportion of PM2.5, allergens, and fungal spores. The recommended replacement frequency is twice yearly – before the heating season in autumn and after it in spring.
How we fit trickle vents in GEALAN S8000 and S9000 windows
Our GEALAN S8000 window systems (Uw down to 0.78 W/m²K) and GEALAN S9000 (Uw from 0.71 W/m²K) are factory-prepared for trickle vent installation whilst maintaining excellent insulation values.
Installing standard trickle vents requires routing slots in the window profiles. Routing creates elongated slots with controlled geometry and smooth edges – air flows smoothly without turbulence or noise. An alternative is MACO VENT – installation with two screws without any intervention in the profile structure. This solution is ideal for those who want to fit trickle vents themselves or add them to existing windows.
→ GEALAN S8000 System – proven universal solution
→ GEALAN S9000 System – certified energy-efficient windows
Important: When even the best trickle vents won’t eliminate moisture from your home
Trickle vents are effective only under one condition: a functioning extract ventilation system. If your home has an extraction problem, trickle vents may not solve it.
The mechanism is simple. Trickle vents supply air to rooms, but natural ventilation through ducts is responsible for removing it. If the ducts aren’t working properly – blocked, too short, or simply lacking the temperature differential to drive airflow in summer – an imbalance occurs. Inflow exceeds outflow. Air enters through the vents but has nowhere to exit.
Simple test: Hold a sheet of paper against the extract grille in the bathroom or kitchen. If the paper is drawn in and stays in place – the extract is working properly. If it doesn’t hold or falls off – you have an extract ventilation problem. In such cases, the solution is hybrid ventilation (mechanical extraction assistance whilst retaining trickle vents) or full heat recovery ventilation.
Heat recovery ventilation in practice: How to reclaim up to 90% of heat and reduce energy bills
Heat recovery ventilation (MVHR) is a closed mechanical ventilation system. The central unit draws fresh air from outside, passes it through filters and a heat exchanger, where it’s warmed by heat from the extracted air. The result: fresh, warm, clean air flows into rooms without opening windows.
The heart of the system: Cross-flow, counter-flow, or enthalpy heat exchanger?
Cross-flow heat exchangers offer 50–60% efficiency. The air streams cross at a 90-degree angle. They’re susceptible to frosting on very cold days, which requires activating energy-intensive electric heaters. This is the choice for budget installations.
Counter-flow heat exchangers achieve 75–90% efficiency. The streams flow parallel in opposite directions over a longer path, allowing more effective heat transfer. This is currently the standard in energy-efficient construction and the best choice for passive houses.
Rotary (enthalpy) heat exchangers have thermal efficiency of 55–80% but offer an additional benefit: they recover not only heat but also moisture. The rotating wheel transfers humidity from bathroom extract air to the supply air. This solves the problem of winter air drying, maintaining humidity in the optimal 35–45% range.
Does heat recovery ventilation dry out the air in winter?
This myth appears regularly: “MVHR dries out the air in winter.” In fact, any ventilation system that works effectively – including natural ventilation and trickle vents – lowers relative humidity in winter. The mechanism is always the same: cold outdoor air contains very little absolute moisture. When you heat it to room temperature, its relative humidity drops.
This happens in homes with both MVHR and trickle vents. It’s a basic principle of thermodynamics. The difference is that a rotary heat exchanger in an MVHR system can recover 40–60% of moisture from extracted air and transfer it to the supply – a solution unavailable in natural ventilation systems.
Which windows for homes with MVHR? Why Yawal TM 102HI is the ideal choice
A home with MVHR needs windows without trickle vents. Heat recovery ventilation is a closed system – air enters ONLY through the central unit. Trickle vents in windows would disrupt the airflow balance and reduce system efficiency.
For homes with MVHR, we recommend Yawal TM 102HI aluminium passive house windows with Passive House Institute certification and a thermal transmittance of Uw from just 0.58 W/(m²K). The 102 mm frame depth with thermal isolator allows for monumental glazing with sash weights up to 300 kg – ideal for modern passive houses with large glass expanses.
→ Yawal TM 102HI Passive House Aluminium Windows – PHI certified
Making the right choice in 2025: What works for new builds vs existing homes
Scenario 1: Building a new home and regulatory requirements
At the design stage, the choice is fairly clear: heat recovery ventilation. Current building regulations effectively mandate energy-efficient solutions, and meeting energy consumption standards with natural ventilation alone is difficult without additional investments.
Installing MVHR in a home built from scratch is significantly simpler than attempting to retrofit it later. Ductwork can be concealed within walls and ceilings during construction, rather than struggling to hide it afterwards in boxing and suspended ceilings. The cost of MVHR (€4,000–6,500 for a 120–150 m² home) is partially offset by savings on ventilation chimneys and trickle vents. Additionally, many countries offer grants and incentives for energy-efficient ventilation systems.
Scenario 2: Renovating an older home with a limited budget
This is the more challenging situation and requires compromises. Installing MVHR in an existing building is a substantial undertaking – walls must be drilled through, ducts routed through living spaces, and ceiling layouts often need changing.
If this isn’t within your budget, trickle vents are a sensible compromise. You achieve rapid improvement in comfort: elimination of moisture, mould, and stuffiness. It’s not an ideal solution, but significantly better than leaving the problem unaddressed.
Most importantly: Before fitting trickle vents, check whether your natural ventilation works at all using the paper test at the extract grille. If the paper doesn’t hold – you have an extract ventilation problem, and trickle vents may not help.
Scenario 3: Small home up to 80 m² – Is MVHR worth it?
In small homes, the economics change. MVHR costs nearly the same as in a larger home (the cost of the unit and installation is similar), but savings are proportionally smaller – fewer square metres to heat means lower baseline bills.
In this situation, trickle vents may be a sensible choice, particularly if the home has functioning natural ventilation. It’s a reasonable compromise between cost and comfort.
4 common ventilation concerns: Noise, draughts, and retrofitting existing windows
Are trickle vents noisy?
The noise level of standard models is 30–40 dB. If you live near a busy road, external noise drowns this out. But in a quiet suburban area, especially in winter during strong winds, it may be audible at night. Acoustic vents with attenuation up to 41 dB are available, comparable to the parameters of the entire window. Before purchasing, it’s worth honestly asking yourself: will this really bother me?
Do trickle vents let heat escape?
Outside air enters cold and must be heated to room temperature. This requires energy. The difference between trickle vents and simply opening windows lies in control – trickle vents introduce air more efficiently than opening windows wide.
Trickle vents aren’t installed to save on energy bills, but to eliminate health and building problems: moisture leading to mould, stuffiness causing headaches, high CO₂ concentration reducing concentration. Significant energy savings come only from heat recovery ventilation.
Retrofitting trickle vents to installed windows – is it possible?
Yes, trickle vents can be fitted to existing windows. Standard trickle vent installation involves routing special slots in the window frame. An alternative is MACO VENT rebate vents, which are fitted with just two screws without any intervention in the profile structure. This solution is ideal for those who want to install trickle vents themselves.
Hybrid approach: Can you combine MVHR with trickle vents?
This isn’t recommended. MVHR is a closed system. If you have trickle vents in windows, you’re introducing cold outside air bypassing the central unit and heat exchanger. This air doesn’t pass through filters, isn’t warmed by recovered heat, and disrupts the airflow balance in the installation. System efficiency drops.
The rule: Either airtight windows plus MVHR, or windows with trickle vents plus natural ventilation.
When to invest in MVHR, and when trickle vents are enough
Micro-ventilation is an emergency function for brief airing, maximum 15–30 minutes. For continuous ventilation, the optional MACO Secuair system available in our hardware is a better solution, allowing safe ventilation whilst maintaining RC2 security rating.
Trickle vents are the solution for renovating older homes. Condition: functioning natural ventilation verified by the paper test at the extract grille. They’re a tool for improving comfort – eliminating moisture, mould, stuffiness – not for energy savings.
Heat recovery ventilation is the choice for those building new homes. In new construction, it’s practically standard, driven by building regulations. Problems with ventilation – condensation on windows, mould in room corners, morning grogginess – don’t disappear on their own. Act now, before poor ventilation starts affecting your home and health.
