Updated on 21.8.2026.
What Should Be Considered When Planning a Ventilation Renovation?
Planning a ventilation renovation in a detached house begins with a comprehensive assessment of the building’s current condition and overall energy consumption. In many older homes, the ventilation system has a low annual heat recovery efficiency, which leads to significant heat losses and reduced energy efficiency.
When planning the renovation, it is essential to evaluate both the performance of the ventilation system and the airtightness of the building so that the new system can be sized correctly. At the same time, opportunities to upgrade to a more energy-efficient solution, such as a mechanical supply and exhaust ventilation system equipped with heat recovery, should be considered.
A thorough assessment of the existing conditions, combined with a comparison of available technical solutions, provides the foundation for a cost-effective and long-lasting renovation that improves indoor comfort and significantly reduces energy consumption.
Which Ventilation Unit Is the Right Choice for a Renovation?
When selecting a ventilation unit, it is worth taking a closer look at the MyVallox 125 CFi range, which has been specifically designed for renovation projects.
Equipped with constant airflow fans, MyVallox 125 CFi ventilation units can replace dozens of older ventilation unit models either directly, without any duct modifications, or with only minor alterations.
The MyVallox 125 units can replace several older Vallox models without requiring ductwork changes, including MUH Ilmava, Ilmava 100, Ilmava 120, Vallox Digit, Vallox 75, Vallox 95, and Vallox 121. They can also replace units from other manufacturers, such as Ilto 440, Ilto 270, Ilto 280, Ilto 290, and Onnline 130 ventilation units.
With duct modifications of only a few millimeters or centimeters, the MyVallox 125 can replace more than 50 different older ventilation unit models in total.
In this article, we have compiled practical tips on what to consider during a ventilation renovation and how to choose the right MyVallox 125 model for your needs..
1. Ensure adequate air volumes
You may use the air volumes of the old unit as a starting point, but you should also check a few things:
- Were the air volumes of the old unit correctly designed? For instance, in the 1980s, the unit and/or ducts could be undersized, particularly with respect to today’s needs.
- Have extensions been built to the house or have wet rooms been added, making the air volumes of the old unit are insufficient?
- Keep in mind that if only the ventilation unit is replaced, there is no obligation to fulfil the current air volume guidelines. If work subject to a building permit is carried out in connection with the upgrade, it is possible that the ventilation system must also meet the current requirements.
- To determine the suitable air volumes, it is advisable to use the services of a ventilation professional. Remember that a professional must readjust the air volumes also after the replacement of the ventilation unit.
2. Check the duct outlets and the dimensions of the frame of the unit
- Check the handedness of the unit (L/R), the number of duct outlets as well as the diameter and locations of the ducts in the unit’s duct outlet, i.e. the ceiling part. Compare them to the dimensional drawings in the replacement table.
- If the old unit has outlet collars with rubber seal rings (male), a duct connector is needed for the duct outlets to connect the ducts to the unit.
- Duct connectors are also needed for connecting the ceiling mounting plate to the ducts.
- The external dimensions of the new unit may differ from those of the old one. Ensure that there is enough room for installation!
- Check whether the vertical space allows the use of a ceiling mounting plate that makes the installation easier.
- You should also leave enough room around the unit for maintenance procedures, such as filter replacement and removal of the heat recovery cell for cleaning.
Replace dozens of old ventilation unit models
For instance, the new Vallox 125 ventilation unit can replace MUH Ilmava, Ilmava 100, Ilmava 120, Vallox Digit, Vallox 75, Vallox 95, Vallox 121, Ilto 440, Ilto 270, Ilto 280 and Onnline 130 and dozens of other old ventilation units. With minor changes in duct outlets Vallox 125 can replace over 50 old ventilation unit models.
Check all replaceable ventilation units in a separate correspondence table below.
3. Take into account the differences between different ventilation units
- Thanks to their outstanding efficiency, new ventilation units condense significantly more water than older models. Therefore, the condensing water must be led into the drain.
- The MyVallox 125 unit has no liquid circulation post-heating radiator, as modern heat recovery cells heat the supply air efficiently enough, so that post-heating is not needed, except during the coldest hours of the year.
- MyVallox 125 does not have a pre-heating/cooling radiator that could be connected to the geothermal heat collection circuit (cf. Digit 2 MLV), but it can be used to control a separate Vallox MLV duct radiator.
- If a so-called circulating air duct has been connected to an old ventilation unit (from above the fireplace, for instance), it must be plugged or connected to the supply air duct.
- A MyVallox control panel is included in the delivery of the MyVallox 125 unit. A NOMAK cable must be installed between the control panel and the unit.
- The MyVallox 125 unit can also be controlled with a cooker hood (Vallox X-Line PTXP MC, Vallox X-Line PTXPA MC or Vallox Delico PTD EC), in which case air exits the cooker hood through the ventilation unit. In connection with the replacement of the ventilation unit, it is also possible to install a separate cooker hood that will remove cooking smells more efficiently directly out of the apartment. In this case, a general extraction valve must be installed in the kitchen.
4. Improve the insulation and sound attenuation of the ducts if necessary
Even if the duct outlets matched the duct outlets of the new unit perfectly, it is advisable to also check the condition of the insulation of the duct when replacing the unit:
- Remember that the exhaust air duct must have condensate insulation over the entire length inside the vapour barrier.
- If the exhaust air duct is difficult to insulate, a wall-mounted air blow-out is worth considering.
When replacing a ventilation unit, consider whether you need better sound attenuation:
- If the noise from the valves is disturbing, replacing the unit will not solve the problem. Instead, silencers should be installed in the ducts or old silencers replaced with ones that dampen the noise of the new unit more efficiently.
- The DC fans of the MyVallox 125 models have a different sound than the old AC fans, which means that different frequency bands are emphasised. The type of the silencer must correspond to the fan noise by frequency band
- Also take other differences into account
Replacing an old ventilation unit in a 1990s house
Supervisor Lassi Saarikko from Kangasalan Putkilämpö recommends thinking ahead as regards the purchase of a new ventilation unit: it is better that it is you, not the broken unit, who determines the time of the replacement.
“A ventilation renovation project, from dismantling the old unit to installing a new one, takes a couple of days. Vallox 125 MV is designed to fit to the duct outlets of the old units. Therefore, there is very little need to adjust the ducts when installing the new unit.”
MUH Ilmava – the best-seller of its time
The manufacture of the best-selling MUH Ilmava ventilation units began at Valmet’s factory in Loimaa in late 1983. With minor modifications, Ilmava units were in production until the 2000s with over 70,000 units sold in.
Vallox 125A MV ventilation units have been designed and manufactured at the same factory as MUH Ilmava and the subsequent Ilmava models. An MUH Ilmava unit can be replaced with a MyVallox 125A CFi unit without an adapter, as the units have six identical duct outlets.
MyVallox 125 CFi ventilation unit solved a family’s problem with negative pressure
The indoor air quality in a detached house in Rovaniemi improved significantly when an old ventilation unit was replaced with MyVallox 125 CFi, equipped with a constant flow feature.
LVI Kemppi, the company that installed the new ventilation unit, finds Vallox’s products reliable and praises the innovative constant flow feature that makes setup easier and provides balanced ventilation.
