Hello everyone!
I have been reading and researching online and in this forum for a long time now, but unfortunately, I’m still not much wiser when it comes to mechanical ventilation with heat recovery.
My partner and I are planning a single-family house (160 m² (1,722 ft²)) with gas and solar energy, built to the KfW-70 standard. Now we are wondering whether we should install a ventilation system.
Friends of ours have a decentralized ventilation system in their new build and are very happy with it—they can’t imagine living without it anymore.
However, in various forums, people often say that for new builds, a centralized system is better. The whole ducting, with maintenance and the potential for germs, gives me a weird feeling... I would constantly wonder what’s actually in the air inside my home. Is that a misguided concern?
And is the decentralized ventilation really that much worse than the centralized system? You hear that a lot.
What kind of costs should we roughly expect for a ventilation system? Is it true that centralized and decentralized systems cost about the same?
Thank you very much for all your advice!
Goldbeere
I have been reading and researching online and in this forum for a long time now, but unfortunately, I’m still not much wiser when it comes to mechanical ventilation with heat recovery.
My partner and I are planning a single-family house (160 m² (1,722 ft²)) with gas and solar energy, built to the KfW-70 standard. Now we are wondering whether we should install a ventilation system.
Friends of ours have a decentralized ventilation system in their new build and are very happy with it—they can’t imagine living without it anymore.
However, in various forums, people often say that for new builds, a centralized system is better. The whole ducting, with maintenance and the potential for germs, gives me a weird feeling... I would constantly wonder what’s actually in the air inside my home. Is that a misguided concern?
And is the decentralized ventilation really that much worse than the centralized system? You hear that a lot.
What kind of costs should we roughly expect for a ventilation system? Is it true that centralized and decentralized systems cost about the same?
Thank you very much for all your advice!
Goldbeere
A
AndyT240523 Dec 2011 11:45Hello everyone,
Here’s a brief experience and opinion about mechanical ventilation with heat recovery:
We have been living in our house with this ventilation system since the end of February and are absolutely thrilled with it.
I believe the best proof of the effectiveness of mechanical ventilation with heat recovery is this:
We have two dogs, and as you might expect, they do have that typical dog smell—especially when it rains. People who don’t own dogs immediately noticed the dog odor in our old apartment.
Now, visitors tell us that they don’t notice any odors in our house—no dog smells, no cooking smells, nothing.
For us, mechanical ventilation with heat recovery is clearly also a comfort gain, as we don’t need to open the bathroom windows after bathing or showering to ventilate.
Our hygrometer usually shows around 80% humidity after a bathroom session, which then stabilizes to around 45%-50% after about 15 minutes.
In our view, this ventilation system has clearly been a very worthwhile investment.
Best regards,
AndyT2405
Here’s a brief experience and opinion about mechanical ventilation with heat recovery:
We have been living in our house with this ventilation system since the end of February and are absolutely thrilled with it.
I believe the best proof of the effectiveness of mechanical ventilation with heat recovery is this:
We have two dogs, and as you might expect, they do have that typical dog smell—especially when it rains. People who don’t own dogs immediately noticed the dog odor in our old apartment.
Now, visitors tell us that they don’t notice any odors in our house—no dog smells, no cooking smells, nothing.
For us, mechanical ventilation with heat recovery is clearly also a comfort gain, as we don’t need to open the bathroom windows after bathing or showering to ventilate.
Our hygrometer usually shows around 80% humidity after a bathroom session, which then stabilizes to around 45%-50% after about 15 minutes.
In our view, this ventilation system has clearly been a very worthwhile investment.
Best regards,
AndyT2405
Well. A system with many inaccessible pipes inside the house might have some advantages for air exchange. However, I believe it is more than likely that germs and bacteria will accumulate inside the pipes over the years and then be distributed throughout the entire house.
Furthermore, such a system always creates a slight draft, which may not be noticeable to most people. But if someone is very sensitive to it, they will always find it disturbing.
Regarding mold growth, I think that a poorly insulated house (older building) is more prone to mold because moisture settles on cold exterior walls.
Everything has its pros and cons.
Regards
Furthermore, such a system always creates a slight draft, which may not be noticeable to most people. But if someone is very sensitive to it, they will always find it disturbing.
Regarding mold growth, I think that a poorly insulated house (older building) is more prone to mold because moisture settles on cold exterior walls.
Everything has its pros and cons.
Regards
Bauexperte schrieb:
Hello,
Quite rare....
To prevent water vapor condensation in multi-layer building components, the thermal resistance should increase from the inside to the outside (insulation layer on the outside) and the vapor resistance should decrease accordingly. These conditions are met, for example, in wall assemblies such as: interior plaster, sand-lime masonry units, solid bricks, mineral wool insulation, air gap, facade panel (wall with ventilated façade). If the wall remains damp—which is especially important to consider in new buildings—then water behind a waterproof or water-repellent outer layer, such as might occur with some thermal insulation membranes, cannot easily escape by diffusion, and the masonry can be damaged over a long period.[1]
[Source 1] Kur, Friedrich; Wohngifte, Handbook for Healthy Building and Furnishing
Thanks to planners at the drawing board in Brussels, this is a relic from the good old days; nowadays, at least small ventilation flaps for windows are offered again—which is better than nothing.
It’s not that simple; in the evenings and at night, occupants are usually at home, and not all moisture can be removed by ventilating twice a day—including moisture from the morning bathroom routine.
Moisture inevitably occurs in new buildings, even though many masonry units are now bonded—less so than before, but with the screed still plenty of water enters the building, and external thermal insulation composite systems (ETICS) do not make this any easier. It is what it is.
Kind regards
B
Bauexperte26 Dec 2011 12:09Hello,
That is a misconception. In fact, except for a few exceptions, the opposite is true. It is the highly insulated houses with external thermal insulation composite systems (ETICS) that have actually encouraged mold growth.
Kind regards
S.D. schrieb:
Regarding mold growth, I think that a poorly insulated house (older building) is more prone to mold because moisture settles on cold exterior walls.
That is a misconception. In fact, except for a few exceptions, the opposite is true. It is the highly insulated houses with external thermal insulation composite systems (ETICS) that have actually encouraged mold growth.
Kind regards
Bauexperte schrieb:
Hello,
That is a misconception; actually, it is the other way around—with few exceptions. It was the highly insulated houses with external thermal insulation composite systems (ETICS) that caused mold problems to increase.
Kind regardsSorry Bauexperte, but I don’t quite understand that.
Basically, an ETICS raises the surface temperature of exterior walls. This is often a problem in uninsulated older buildings because condensation tends to form in corners on the outside walls, which ultimately leads to mold growth.
An ETICS raises the surface temperature so that mold can no longer develop.
Mold growth can, of course, occur if the residents do not ventilate regularly. However, this has nothing to do with the ETICS; rather, it is related to other factors that have affected the previously existing air exchange (such as new windows and doors).
A wall itself does not breathe, so there is no air exchange through the walls.
Best regards
B
Bauexperte26 Dec 2011 13:16Hello,
To prevent mold growth, it is first necessary to understand the conditions under which it develops. There are four factors that inevitably lead to mold formation when they occur together.
- First, there is the humidity. If it is relatively high, this is a crucial prerequisite. Experts state 65 percent relative humidity as the lower limit. Wood is a good substrate for mold if its moisture content exceeds 30 percent.
- Temperature must also be suitable. The most problematic range is between 18 and 25 degrees Celsius (64 and 77°F), which are the typical temperatures inside homes.
- Mold needs a food source. It feeds on cellulose, which can be found almost everywhere in a house – in wallpaper, adhesive paste, plaster, or paint.
- Finally, the pH value of the surface should be approximately between 4 and 7.
When these conditions coincide, mold growth is almost inevitable.
About 10 years ago, it often took more than 18 months from the first groundbreaking to the homeowners moving in when building a solid masonry house. During construction, the house usually stood as a shell through a winter; the water in the building materials was supposed to “freeze out.” Today, however, a solid masonry house is typically ready to move into after no more than 9 months. The moisture in the building materials usually does not evaporate completely – so the house contains more residual moisture than before.
Another common scenario is when an existing house is renovated and insulated against heat loss. Where doors and windows were previously not airtight, now practically nothing passes through – no heat, but also no condensation. This condensation then settles on wall surfaces, wallpaper, and paint – a perfect breeding ground for various mold fungi.
A three-person household produces on average about ten liters (2.6 gallons) of water vapor per day, mainly through cooking, showering, and washing. In the past, this moisture could escape through drafty windows and doors or condense on single-pane windows. The ventilation was essentially built-in to the poorly insulated house.
Today, it is different: the increasing energy efficiency measures in houses literally encourage mold growth and thus increase health risks. A well-known example: single-pane windows in older buildings are replaced with double or triple glazing without simultaneously insulating the walls. The result: the water vapor no longer condenses on the windows but on the coldest spots instead. These are often the corners of exterior walls, concrete lintels above windows, or radiator niches, where walls are generally thinner. Mold forms on these so-called thermal bridges. Condensation can also occur behind furniture or pictures placed against exterior walls. The reason is that the exterior wall cools down because warm indoor air cannot circulate behind these objects.
In newly built houses constructed to current thermal insulation standards and with external thermal insulation composite systems (ETICS), mold can spread if ventilation is not done properly. In massive construction new builds, considerably more ventilation is required during the first year than usual because the walls still contain moisture.
The only alternative to controlled mechanical ventilation is dry heating. This means not only running the radiators but also frequently airing out the humid indoor air. The magic word is “shock ventilation” or “rapid airing.” This involves opening the windows wide, letting the indoor air escape within a few minutes, closing the windows again, and ideally repeating this several times a day.
It is also helpful if, during the construction of a presumably well-insulated house, windows with forced ventilation systems were selected. Although this cannot replace rapid airing, it significantly supports the effect.
Best regards
S.D. schrieb:
Sorry Bauexperte, but that is not entirely clear to me.
To prevent mold growth, it is first necessary to understand the conditions under which it develops. There are four factors that inevitably lead to mold formation when they occur together.
- First, there is the humidity. If it is relatively high, this is a crucial prerequisite. Experts state 65 percent relative humidity as the lower limit. Wood is a good substrate for mold if its moisture content exceeds 30 percent.
- Temperature must also be suitable. The most problematic range is between 18 and 25 degrees Celsius (64 and 77°F), which are the typical temperatures inside homes.
- Mold needs a food source. It feeds on cellulose, which can be found almost everywhere in a house – in wallpaper, adhesive paste, plaster, or paint.
- Finally, the pH value of the surface should be approximately between 4 and 7.
When these conditions coincide, mold growth is almost inevitable.
About 10 years ago, it often took more than 18 months from the first groundbreaking to the homeowners moving in when building a solid masonry house. During construction, the house usually stood as a shell through a winter; the water in the building materials was supposed to “freeze out.” Today, however, a solid masonry house is typically ready to move into after no more than 9 months. The moisture in the building materials usually does not evaporate completely – so the house contains more residual moisture than before.
Another common scenario is when an existing house is renovated and insulated against heat loss. Where doors and windows were previously not airtight, now practically nothing passes through – no heat, but also no condensation. This condensation then settles on wall surfaces, wallpaper, and paint – a perfect breeding ground for various mold fungi.
A three-person household produces on average about ten liters (2.6 gallons) of water vapor per day, mainly through cooking, showering, and washing. In the past, this moisture could escape through drafty windows and doors or condense on single-pane windows. The ventilation was essentially built-in to the poorly insulated house.
Today, it is different: the increasing energy efficiency measures in houses literally encourage mold growth and thus increase health risks. A well-known example: single-pane windows in older buildings are replaced with double or triple glazing without simultaneously insulating the walls. The result: the water vapor no longer condenses on the windows but on the coldest spots instead. These are often the corners of exterior walls, concrete lintels above windows, or radiator niches, where walls are generally thinner. Mold forms on these so-called thermal bridges. Condensation can also occur behind furniture or pictures placed against exterior walls. The reason is that the exterior wall cools down because warm indoor air cannot circulate behind these objects.
In newly built houses constructed to current thermal insulation standards and with external thermal insulation composite systems (ETICS), mold can spread if ventilation is not done properly. In massive construction new builds, considerably more ventilation is required during the first year than usual because the walls still contain moisture.
The only alternative to controlled mechanical ventilation is dry heating. This means not only running the radiators but also frequently airing out the humid indoor air. The magic word is “shock ventilation” or “rapid airing.” This involves opening the windows wide, letting the indoor air escape within a few minutes, closing the windows again, and ideally repeating this several times a day.
It is also helpful if, during the construction of a presumably well-insulated house, windows with forced ventilation systems were selected. Although this cannot replace rapid airing, it significantly supports the effect.
Best regards
Now the question is which is the lesser evil: a poorly insulated exterior wall where condensation forms, or a well-insulated wall (plus window) where indoor humidity must be removed by ventilation.
I believe that a renovated house with new windows (with trickle vents) does not need to be ventilated more often than before the renovation.
Regards
I believe that a renovated house with new windows (with trickle vents) does not need to be ventilated more often than before the renovation.
Regards
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