Replacing Natural Ventilation with an HRV System: What Is Required in Practice?

Self-draught is a simple ventilation system that relies on temperature differences, wind and leaks in the house. It has worked in many older buildings, but it is also a system that can be uneven. Ventilation can be too weak during parts of the year, while the house releases unnecessary heat once the draught is strong.

FTX is a more controlled way of ventilating. Exhaust air is extracted from, for example, bathrooms, laundry rooms and kitchens, while filtered supply air is supplied to rooms where people are present. The heat in the exhaust air is recovered in The FTX unit and is used to heat the incoming air.

Switching from draught to FTX gives better control of the indoor climate and reduces heat losses. But it is not a change of “one fan for another”. It is a remodelling of the ventilation principle of the house, and it needs to be properly planned.

When is it relevant to switch from draught to FTX?

There are several common reasons why homeowners start looking towards FTX:

• ventilation is perceived as weak or uneven;
• it will be fogging on windows or problems with moisture;
• the air feels trapped in bedrooms and living rooms;
• the house has been additionally insulated or has new, tighter windows;
• you want to reduce heat losses;
• you want filtered supply air instead of air through gaps and leaks.

Especially after renovations, self-draught may not work as well as before. A older houses were often dependent on leaks in the building envelope. When windows, doors, attics or facades are sealed, conditions change. This can make it harder for air to get in, even if chimneys and exhaust air ducts are still in place, and can cause stagnation.

What does FTX mean compared to self-draught?

The big difference is that FTX doesn't wait for weather and temperature differences to create draughts. The system uses fans for both exhaust and supply air. This allows airflows to be sized, adjusted and balanced.

The air supply must be planned

In a self-draught house, there are often exhaust air ducts already in place, for example in the bathroom, WC, kitchen or through the brickwork. This does not mean that the house is prepared for FTX.

For FTX, a supply air system is also needed. The supply air should normally be directed to bedrooms, living rooms and other living areas. This requires ducts, supply air diffusers and a well thought-out routing so that the air is distributed without draughts, noise or unnecessary pressure drops.

This is often where the project is decided. The FTX unit itself is only part of the solution. The ductwork, the positioning of the the adjustments are at least as important for the final outcome.

Can existing channels be used?

Sometimes parts of existing exhaust air ducts can be used, but this must be assessed on a case-by-case basis. Old ducts may be the wrong size, leaky, difficult to clean or located in a way that is not suitable for a balanced FTX system.

It is also common for self-draught to be connected to masonry or older shafts. In this case, you need to examine the condition, tightness, fire requirements and how the ducts actually run. Do not assume that existing ducts can be reused before they are checked.

Where is the FTX unit normally placed?

The unit needs to be placed where it is possible to connect outdoor and exhaust air, supply air and return air in a good way. There must also be space for servicing, filter replacement and condensation management.

Common locations are attics, technical rooms, storage rooms, laundry rooms, utility rooms, boiler rooms or other spaces where servicing is reasonably easy to perform. A location that is practical on the drawing is not always practical in everyday life. Filters need to be changed, sounds need to be handled and ducts need to be routed without unnecessarily long or complicated routes.

Energy is an important part - but not all

FTX is often chosen to reduce heat losses from ventilation. This is a reasonable reason. When heat from the exhaust air is recovered, the heating system does not need to supply as much energy to heat new outdoor air.

But FTX should not only be seen as an energy investment. Just as importantly, the system can provide more even airflows, filtered supply air and better control over how air moves through the house.

It is particularly relevant in bedrooms. Many people notice ventilation deficiencies there first: heavy air in the morning, a stuffy feeling or the need to ventilate often. With a properly designed FTX system, fresh air is supplied where it is needed, while exhaust air is taken from rooms where moisture and odours occur.

Is FTX always the right choice?

No, it isn't. FTX is often a very good solution, but it is not automatically right for all houses. In some buildings, ducting may be difficult, costly or have more impact on the building than you want. In other cases, other ventilation measures may be more reasonable.

The decisive factor is the conditions of the house. A well-designed FTX system can provide both better comfort and lower ventilation losses. A poorly designed system, on the other hand, can create unnecessary noise, draughts, difficult servicing and dissatisfaction.

Common mistakes

1. you start with the unit instead of the house

It is wise to start with a review of the house rather than starting with unit size. A good FTX system is sized according to the building and its use, not the other way round.

Before proceeding, you should find out how the house is currently ventilated, whether there are moisture problems or uneven ventilation, whether the house has become more airtight after renovation and whether there is room for ducting to bedrooms and living rooms. It is also important to assess at an early stage where the unit can be placed, how the noise level is affected, whether a building notification or dialogue with the municipality is needed, and who is responsible for planning, adjustment and documentation.

2. underestimating channelling

It's easy to focus on the unit, but in existing houses, ducting is often the biggest practical issue. Ceilings, joists, closets, attics and shafts may need to be used cleverly to ensure a good installation.

3. choosing too small or too large a unit

A unit should fit the air flows that the house needs. Too small a margin can lead to higher noise levels and poorer operation. An unnecessarily large unit can be more expensive and take up more space than necessary.

4. you forget the sound

Noise from units, ducts and nozzles needs to be addressed at the design stage. The right ductwork, silencers and dimensioning make a big difference.

5. you don't think about service

Supply and exhaust air filters should be changed about 2 times a year and the unit must be checked. If the unit is placed in a confined space or is difficult to access, servicing is easily postponed.

6. sealing the house without ensuring ventilation

When an older house is sealed, self-draught can deteriorate. If you switch to FTX at the same time, you need to think about the house as a whole: the building envelope, air flows, moisture and pressure balance.

7. trying to do too much without the right skills

A change from draught-free to FTX should be planned and installed by people with the right expertise. This involves air flows, noise, duct pressure, fire, condensation, electricity, control and adjustment.

For the homeowner, it is still valuable to understand the basics. It makes it easier to ask the right questions, compare solutions and recognise the difference between a well thought-out installation and a quick, standard solution.

This is what the process can look like

1. Inventory: Review current ventilation, floor plan, ducts, masonry, attic and possible installation routes.
2. Needs assessment: Determine which air flows are needed and which rooms should have supply and extract air.
3. System proposals: Determine the location of the units, ducting, diffusers, sound attenuation and outdoor/exhaust air.
4. Choice of aggregates: Select units based on airflow, efficiency, noise, control, filters and service access.
5. Installation: Install the units, ducts, diffusers, insulation and condensation management according to the designed solution.
6. Adjustment: Measure and balance the air flows to ensure the system is working as intended.
7. Operation and maintenance: Monitor sound, comfort, filter changes and any adjustments after the system has been in operation.

Get a quote for switching to FTX ventilation

Would you like to find out if FTX is suitable for your house? Contact us via the form below and we will help you further. We will go through the basic conditions and connect you with one of our partners who can return with a quote for switching to FTX ventilation.