When people talk about ventilation, most only think of ducts and fans. Of course, those are part of our everyday work at IVAeris Oy. But the truth is, before mechanical ventilation, there was natural ventilation – a system that harnessed the power of nature: wind and temperature differences. It’s not just outdated technology; it’s still a completely relevant solution if you know what you’re doing. And that’s exactly why we’re here.
Natural ventilation isn’t just some “museum technology” moving air around. In reality, many professionals are too quick to recommend switching to mechanical ventilation, but that’s not always necessary. Natural ventilation works based on nature’s own principles – the temperature differences between indoor and outdoor spaces, and the wind, create pressure differentials that move the air. But here’s the thing: it’s not always as simple as it sounds. If you want to maximize efficiency, you can add a fan that steps in when natural forces aren’t enough. This is fan-assisted natural ventilation – a smart way to boost the system when you need more power.
Can you combine both natural and mechanical ventilation in the same building? Yes, you can, but it has to be done wisely. It’s not enough to throw them together and hope for the best – the airflow directions must not cross. For example, you can install mechanical ventilation in the bathroom and keep natural ventilation in the rest of the house. The key is to keep the systems separate and manage them without leaks or mixed airflow. And preventing air leaks is crucial. If the exhaust duct isn’t sealed, expelled moisture can start seeping into the structure, and that’s when you’re in trouble. Moisture leads to the growth of microbes and mold – a nightmare no one wants.
Hybrid ventilation – that’s the magic word. It means using both natural and mechanical systems smartly, when it makes sense. But even though it’s a hybrid, it’s officially classified as natural ventilation according to regulations.
Where does natural ventilation work best?
Natural ventilation shines in smaller residential buildings – single-family homes, townhouses, and small apartment buildings are ideal settings. But the world has changed. The way we live has changed. In the past, wood-burning stoves kept the exhaust chimneys warm, but today they no longer play the same role. Additionally, modern lifestyles – larger wet areas, increased water usage, and internal heat loads – challenge the old ventilation solutions.
Nowadays, allergies, sensitivities, and pollution make proper ventilation more critical than ever. You can no longer just copy old solutions into new buildings without careful planning. You need to measure, calculate, and optimize – only then will natural ventilation work like a dream.
Natural ventilation: How does it really work?
Natural ventilation is radically different from mechanical ventilation. It’s not just a “turn on the fan and the job is done” kind of system. In this game, the winner is the one who knows how to harness natural forces: temperature differences between indoor and outdoor air, and the wind, drive the airflow. But here’s the challenge – this system isn’t always consistent. It reacts to weather and the seasons, making its performance a bit harder to evaluate and measure compared to mechanical systems.
Here are a few key points you need to know about natural ventilation:
System design is a whole process – You can’t just jump into the middle of a project and switch from mechanical ventilation to natural ventilation. The plan needs to be built with that in mind from the very beginning.
“Adjustment” is relative – The settings of the vents need to adapt to changes in outdoor temperature and wind, to keep airflow roughly at the desired level. However, it’s important to note that in this context, “adjustment” is used loosely, as natural ventilation airflow can only be increased or decreased, but not precisely controlled.
The limits of filtration and noise reduction – Compared to mechanical systems, natural ventilation offers much more limited options for outdoor air filtration and noise reduction.
Before 1987, natural ventilation was a standard solution in many buildings. Today, it’s mostly used in quiet, pollution-free areas. However, natural ventilation hasn’t lost its relevance – it remains a powerful solution when designed correctly.
Laws and regulations on natural ventilation
The game for natural ventilation changed drastically in 1987 when building regulations were tightened. Previously, ventilation was largely managed by nature, but it has since been limited to quiet, pollution-free areas. However, in the modern world, things don’t work that way anymore. All ventilation systems are expected to meet certain standards – and rightly so.
Let’s go over what modern laws and regulations say about ventilation. By early 2018, legislation was fully updated in conjunction with the Land Use and Building Act. This means that if you want to stay informed, you need to know these regulations. The laws are easily accessible on Finlex (www.finlex.fi), so there are no excuses for not staying up to date.
First of all, the Ministry of the Environment’s decree (1009/2017) regulates everything from airflow rates and directions to temperature and filtration. Every new building, extension, or addition of space is covered by this regulation – except for vacation homes and agricultural buildings. Noise environments are also regulated (796/2017) because noise and acoustics are a big part of well-being. No one wants to live or work in a place where the sound environment is nerve-wracking.
What about energy efficiency? The Ministry of the Environment’s energy efficiency decree (1010/2017) came into play and set the E-value limits – the energy efficiency of each building is measured using these values. While natural ventilation might seem outdated, it is still relevant if you know how to make it work. The efficiency of heat recovery from exhaust air in natural ventilation is zero, meaning you can’t compensate for it with better insulation. However, if you add a fan to the system, electricity consumption is factored into the E-value.
Then there’s the Housing Health Decree (545/2015), which sets strict health requirements for indoor air and ventilation. When there is a suspected health issue in a home, this decree comes into play. No half-measures when it comes to health.
The Land Use and Building Act defines the requirements for fire safety, health, and energy efficiency in ventilation. Building control authorities can grant minor deviations in building permits, but only if they don’t compromise these key requirements. If you’re seeking an exemption, you need to justify it properly.
In summary: if you’re planning a ventilation system, you need to know the rules of the game. It all starts with the right products and understanding how their technical properties, like airflow rates and noise levels, fit into the bigger picture.
How do you ensure that natural ventilation meets all regulations?
In building codes, natural ventilation is still an acceptable solution, but legislation sets clear requirements for airflow rates, flow directions, temperature conditions, and air filtration. These regulations apply to new buildings and extensions, so if you’re planning natural ventilation, you must ensure compliance with these standards.
Here’s how to proceed if you want to implement natural ventilation:
Preliminary consultation – Consult with the building control authorities to clarify their stance and check if the location is suitable.
Qualified designer – The designer must have the right qualifications and experience. No room for amateurs.
Plan – Design the system properly and create a plan that outlines the system’s performance and technical solutions.
System report – This is a document where you explain how you will address the challenges of natural ventilation and ensure its functionality.
Qualified supervision – You’ll need a competent site manager to ensure that the system is installed correctly.
Commissioning and measurement – The system’s airflow is measured and, if possible, adjusted. However, it’s important to note that in this case, “adjustment” is used quite loosely, as natural ventilation airflow can only be increased or decreased but not precisely controlled.
Natural ventilation isn’t an outdated solution – it’s just a different game. When you know the rules and how to play this game, you can achieve a functional and efficient ventilation system that serves you for decades.
Monitoring indoor air quality is crucial, and environmental monitoring provides accurate data on what’s happening in your spaces. It can reveal carbon dioxide levels or humidity in wet rooms. This real-time tracking ensures your ventilation system works as it should and provides essential feedback on the system’s performance. A well-functioning ventilation system is no accident; it’s a carefully designed and monitored setup.
Problems and solutions for natural ventilation
Natural ventilation works like a dream for most of the year in Finland… because for most of the time, we have winter. Cold outdoor air and warm indoor air create the perfect conditions for air movement naturally – thanks to the temperature difference. But you know the famous Finnish summer? Those couple of days of sunshine that people talk about all year? Well, that’s when the real challenges for natural ventilation come into play.
When outdoor and indoor temperatures are similar, and there’s no wind, ventilation can practically come to a halt. The air becomes stagnant, and suddenly, the building feels stuffy. The traditional solution? Open the windows. Sure, it’s easy, but not always the smartest option – especially when noise, pollution, or unwanted guests can enter as well.
But nowadays, we can do much more. We’re no longer limited to just opening windows. This is where modern solutions come into play, helping to keep the air moving even when nature doesn’t provide the boost.
A little mechanical help for natural ventilation
Sometimes natural ventilation needs a little boost, and one smart way to achieve this is by installing a draft enhancer. This device is literally simple but an effective way to increase airflow, especially in ducts and chimneys where the draft isn’t great. The draft enhancer has a turbine that spins with the power of the wind – no matter the direction or speed. It’s in constant motion, ensuring that ventilation works all the time, either more or less. And the best part? It prevents the air from reversing, which is critical. Since it’s made of stainless steel, this device can handle anything the Finnish weather throws at it.
If you want something more active, you can install an exhaust fan in the bathroom or toilet. This doesn’t override the natural system but ensures that air moves, even when outdoor conditions aren’t ideal. A low-blade axial fan is a smart choice, and you can automate its operation by measuring CO₂ levels or humidity. However, the most common and simple solution is to connect the fan to the light switch – when the light turns on, the fan starts running.
But here’s a word of caution: if the exhaust duct isn’t sealed properly, the moisture in the air being vented out can leak into the building’s structure, and that’s when you’ve got a problem. Moisture in the structure leads to microbial and mold growth, and that’s the last thing anyone wants.
Solar-assisted natural ventilation
Solar ducts are the real game-changer here. When the sun heats the exhaust ducts, it creates a temperature difference that increases the airflow in the solar duct. This works on a simple yet effective principle: warm air rises. As warm air gathers at the bottom of the duct, it naturally rises up through the solar duct.
In winter, the heat naturally comes from the building’s living areas, but in summer, the sun can heat the exhaust ducts through an insulated enclosure with glass. This process supports natural ventilation, especially when the sun is shining brightly.
Ensuring optimal performance? The exhaust duct should be at least 4.5 meters tall, but the taller the duct, the greater the temperature difference and the faster the air rises. This way, you can fully harness nature’s power to enhance airflow.
But that’s not all – the same principle can be used for cooling. A solar duct creates a draft, which generates negative pressure and draws fresh air into the building. If the incoming air is routed through the ground first, you get free, solar-powered air conditioning.
The Germans have already implemented this in their passive houses. They bury a “nose” into the ground near the house, ensuring cool air in summer and mild air in winter. It’s a simple yet smart solution that pays off in energy savings and comfort.
Bottom line? Solar-assisted ventilation isn’t just innovative – it’s a practical and energy-efficient way to enhance airflow and even cool your home using the power of the sun.
Backdraft, condensation, and the effects of wind
Wind direction or high outdoor temperatures can cause backdraft, bringing unfiltered air inside. This is a particularly big issue with kitchen exhaust hoods and fireplaces. If this happens, you have a problem – dirty air flowing into clean areas. But don’t worry, the issue can be resolved:
Install a draft booster at the top of the exhaust duct. It reduces backdraft.
Ensure sufficient replacement air, especially in rooms with a fireplace or kitchen hood.
Condensation and wind can cause issues in exhaust ducts year-round. Exhaust duct design needs to be precise to avoid moisture and airflow problems.
You can’t always rely on air to move naturally. But with a few smart solutions – like fan-assisted ventilation or a solar-assisted duct – you can ensure your natural ventilation system works even when nature isn’t on your side.
Thermal comfort, outdoor air ducts, and supply air windows
In natural ventilation, outdoor air enters unheated, which can cause a draft if the airflow isn’t controlled. Properly placed vents, such as traditional tilting vents or air vents behind heating units, can prevent uncomfortable drafts. Additionally, an outdoor air radiator, which directs air through the radiator’s fins, is an effective way to warm incoming air in winter.
If you want to take it to the next level, you can bring outdoor air into the building through an underground air duct. This duct preheats air in winter and cools it in summer. Just don’t forget to equip the duct with a condensation drain and ensure it’s easy to clean. For even greater efficiency, you can even add a duct heater.
A supply air window can be a smart way to preheat air using both sunlight and heat loss from inside the building. But remember to prevent reverse airflow and window condensation. When using a supply air window, it’s crucial that the vent is adjustable over a wide range. And when you need quick cooling, traditional window ventilation is still a reliable method—especially if you can create a cross-draft by opening windows on opposite sides of the building.
Airflow measurement, energy efficiency, and adjustment
Natural ventilation operates in its own realm – the pressure differences are so small that measuring them is like trying to gauge a breeze indoors. That’s why continuous monitoring isn’t required. However, if you want a clearer picture, a one-time measurement is sufficient, and there are a couple of good tools for that. For instance, you can use carbon dioxide as a tracer to directly measure ventilation rates. Or, if you need more precision, you can measure the airflow of individual vents using a vane anemometer and a measuring hood.
If you’re aiming for next-level precision, ultrasonic sensors have entered the game. They provide continuous airflow measurement without causing pressure drops. It’s important to note, though, that the timing of measurements can impact the results – wind and other external factors can cause significant fluctuations in the readings.
Natural ventilation without heat recovery leads to higher heating energy consumption. The E-number requirements steer you toward energy-efficient solutions, such as using renewable energy. But don’t forget CO₂ emissions – without heat recovery and with high-emission heating, your system’s environmental footprint can increase significantly.
Managing airflow requires users to adjust vents according to outdoor temperatures and wind conditions. Vents need to be user-friendly, and if you can see the impact of vent adjustments immediately, controlling the ventilation becomes much easier.
Designing natural ventilation
When planning natural ventilation, the first thing to check is the building site. If the house is in a noisy area – forget about natural ventilation without proper soundproofing. Filtration is another matter. In almost all cases, filtering reduces the efficiency of the ventilation, but it’s crucial in polluted areas. In Finland, outdoor air quality is generally good, but heavy traffic can still cause issues. If the building site is not at least 200–300 meters away from a busy road, filtration is a must.
In noise- and pollution-free areas, natural ventilation can work perfectly without outdoor air filtration. However, if there’s heavy traffic or other pollution around, make sure filtration is part of the plan. And even if the air quality is good, it’s wise to have a filter option available for temporary situations, such as during pollen season. This isn’t a luxury—it’s survival.
Architectural design – ventilation first
Natural ventilation requires a specific building type, so the architectural design begins with ventilation. It all starts with how the ducts and vents are placed. You can choose between two options:
Transfer air solution: Exhaust ducts are in wet rooms, and air moves there through gaps, like under the door.
Room-specific supply and exhaust solution: Each room has its own supply and exhaust air vents.
If you choose the first option, make sure the ducts are properly sized and strategically placed. The ducts should be tall – at least 4.5 meters – to create sufficient chimney effect. Ideally, ducts should be positioned centrally in the building to ensure a strong draft. If they are too short or poorly placed, the air won’t move effectively, and the entire system will lose efficiency.
Sizing – don’t guess
The sizing of natural ventilation can be done using calculation formulas, but don’t rely solely on gut feeling. If the building is complex and spaces are interconnected, simulations might be the best option. Calculating airflow and thermal comfort requires precision. The effect of wind is difficult to estimate with formulas, so use CFD simulations if you need more accurate data.
Ventilation zones should be designed with closable doors between spaces. Otherwise, airflow mixes, and the system’s efficiency decreases. Also, note that airflow changes when doors are opened – overall ventilation performance won’t decrease, but airflow distribution might shift.
Sizing chimneys and air intake units – don’t compromise
Proper sizing of chimneys is critical. Ensure the height and sizing of the chimneys are adequate – a minimum height of 4.5 meters is a good rule of thumb. If you need larger air volumes, add another chimney. But don’t forget that the chimneys also need to be straight – horizontal sections increase pressure losses and reduce airflow. If you need to add bends, make them gradual and ensure the air flows upward.
When sizing air intake units, ensure the pressure drop is minimal. Use vents that provide enough air during warm weather but can be adjusted for colder conditions. Choose vents with a large free flow area – the fewer obstructions to the airflow, the better the system will function.
IVAeris Oy – solutions for natural ventilation
The functionality of ventilation in a naturally ventilated building is not left to chance. It requires careful planning, ongoing maintenance, and the right solutions. And this is where we come in. IVAeris Oy is a ventilation installation and maintenance company that doesn’t just “get the job done” – we ensure that your building’s ventilation works optimally every day of the year.
We know that natural ventilation can be unpredictable, especially with Finland’s varying weather conditions. That’s why our team of experts will create a customized action plan specifically for your building. Whether it’s improving chimney airflow, adjusting vents, or providing annual maintenance, we handle everything. And it’s not just talk – we actually do what we promise.
Healthy and fresh indoor air is not a luxury; it’s a basic right. Don’t wait for indoor air problems to arise, get in touch with us. We have the expertise, resources, and determination to make things happen.
WE KNOW, WE CARE & WE GET IT DONE
IVAeris Oy
010 206 3000