ᐅ KfW 70 - 36 cm Ytong blocks - Ventilation system

Mycraft schrieb:
The electricity costs are similar for both systems... the central unit has only 2 fans... the decentralized system, on the other hand, has 10 or more... so overall, the total consumption ends up being comparable.

However, with the decentralized system, you need more filters and have to clean the units more often because the heat exchangers, etc., clog much faster than with central systems... Each fan also requires a separate condensate drain and must be installed completely airtight into the wall... and with 10 holes in the wall, the potential for errors is quite high...

Additionally, there is the factor that the fans sometimes fail... and not always within the warranty period... of course, the seller says "They last forever," but that’s not true... and then you have to spend a bit more... and so on.

So first of all – I think it’s good that such points are discussed calmly and clearly. This helps to clear up rumors and half-truths about central and decentralized systems.

As I already mentioned, for our future decentralized system, we need 6 fans with heat recovery (for about 170 sqm (1830 sq ft)), each equipped with a filter, plus 4 exhaust-only fans (which do not have filters). I can’t estimate the price for the two filters in the central system, but for our 6 filters, the annual cost is between 9 and 15 euros each (depending on the filter type). Pollen filters (15 euros) can only be used once in the decentralized system, while others can be washed and reused.

The system can – but doesn’t have to be – cleaned during filter changes, i.e., once a year (in case of heavily polluted outdoor air, changing the filters and cleaning twice a year might make sense). This is relatively simple: unscrew the cover, pull the fan unit out of the duct, clean it, then slide it back in, done. The duct where the fan sits is only as long as the wall thickness. The heat exchanger can be put in the dishwasher or rinsed off (or cleaned in a bucket or wherever).

Condensate drainage – our fans have an external cover (ours will be made of stainless steel). The moist air is discharged outside, condenses on the cover, and drips off a drip edge integrated in the cover. This drip edge ensures that condensate doesn’t run down the exterior wall (which would be undesirable). Of the 5 units installed in the ventilation office, 4 had such a cover WITH a drip edge. Only one brand from Berlin did not include this. The cover is included in the price of the fans with heat recovery. For the exhaust-only fans, we ordered these covers separately.

Fan failure: Well – this can also happen in a central system, right? If the fan is not repairable (or the repair no longer makes sense financially), the fan would have to be replaced. I think this could even result in higher costs with a central system.

Installation error potential: I agree 100% with you here. This was one of the main questions I asked at the ventilation office. How must the fans be installed, and most importantly – how can thermal bridges be avoided? Based on the explanation, I created a neat drawing which I will give to the installer (even if it makes him think I’m crazy). I also plan to take a day off work on the installation day to personally supervise the process (even if the technician finds this annoying).

The only thing that might involve more effort is that you have to carry a ladder from fan to fan and climb up and down each time. With the central system, you change the filters in one location (unless you also have exhaust filters – if I understood correctly). However, if you want to clean the ducts in a central system, you have to go through the entire house, unscrew, dismantle, clean, reassemble (see your link in the other thread). Whether the effort is the same or higher, I can’t really judge.

Well, that all sounds good... drip edges are certainly one option... however, from my observation, condensation and similar issues still occur at the spots where the facade is penetrated by rain and wind... this happens with all systems, so with decentralized units, the facade needs to be cleaned more often.

As you yourself write, the entire unit can be cleaned during the filter change... the word "can" should definitely be replaced with "must"... because the diameter of the systems is relatively small, and with continuous operation, they become quite clogged within a year.

Of course, a fan in a central system can also fail, but with decentralized systems, the likelihood is much higher simply due to the number and size... it’s a simple calculation.

I am in favor of central systems when space and options allow... but first and foremost, I support ventilation in general... so decentralized is definitely better than nothing at all... because that would be the completely wrong path, especially in the era of plastic-covered houses.

Mycraft schrieb:
Yes, that all sounds good... drip edges are certainly one option... however, in my observation, condensation and similar issues still occur in areas where the facade is penetrated, due to rain and wind... this happens with all systems, so with decentralized units, the facade naturally needs more frequent cleaning...

As you wrote yourself, the entire unit can be cleaned during filter replacement... the word "can" should definitely be replaced with "must"... because the diameter of these units is relatively small, and during continuous operation they tend to get clogged within a year...

Of course, a fan in a central system can also fail, but with decentralized units it is much more likely simply due to their number and size... it’s a straightforward calculation...

I prefer central systems if there is sufficient space and options... but above all, I am in favor of ventilation in general... so decentralized is definitely better than nothing... because that would be the completely wrong approach... especially in the era of plastic bag houses.

The external covers are overall larger than the fan or penetration diameter. Therefore, they still offer some protection against wind, weather, and dirt. As mentioned, a major supplier, who often has sales agreements with tradespeople, unfortunately does not offer these covers.

I wrote “can be cleaned” because that depends on the individual. Personally, I believe: “If you invest so much money in building a house, as a homeowner it would be negligent not to give your property the necessary care and maintenance.”

I cannot and do not want to judge whether a decentralized or a central fan is more likely to fail, as I simply have too little experience with this topic. However, I do believe that with appropriate maintenance (see the paragraph above) the lifespan can generally be extended (apart from material defects or manufacturing faults).

Otherwise, I am also an advocate for a ventilation system – with heat recovery. Of course, I had to learn first that despite the projected 90% heat recovery (actually closer to 80%), such a system will never pay for itself financially. But I am already looking forward to the improved quality of life, and that cannot be measured in money.

Hello,

Mycraft schrieb:
Yeah, that all sounds good... drip edges are definitely one option... however, my observation has been that due to rain and wind, condensation and similar issues still occur where the facade is penetrated... with all systems, so of course the facade needs more frequent cleaning with decentralized units...

Regarding the "facade that needs cleaning," I agree with f-pNo. You cannot assume that a single-family house—once built—does not require any maintenance; the same applies to facing facades. Besides, there are various providers for decentralized ventilation systems as well.

Mycraft schrieb:

As you yourself wrote, the entire unit can be cleaned during filter replacement... the "can" can definitely be replaced with "must"... because the diameter of the units is relatively small and with continuous operation they get pretty clogged within a year...

Maybe you could get into the habit of clearly stating that you are only sharing your assumptions?

Any homeowner can easily clean a decentralized system; it is simpler and less labor-intensive than a central system. Normally, the unit itself indicates when the filter needs to be changed. The owner just needs to remove the indoor cover, take out the filter, and insert a new or cleaned filter (filters can be cleaned in the dishwasher, by the way). Then just inform the device that the filter has been replaced, and that’s it. Even if this needs to be done once a year, it is not a huge effort.

The ventilation ducts of a central system, on the other hand, require the presence of a maintenance technician equipped with a camera, vacuum device, and long brushes.

All in all, I would assume—adding up all costs—that the actual cleaning expenses for both systems do not differ significantly.

Mycraft schrieb:

Of course, a fan in a central system can fail as well, but with decentralized systems it is much more likely, simply due to the number and size... that’s a simple calculation...

In recent years, our clients have installed many ventilation systems—both decentralized and central—depending on their preferences and budget. I have not heard complaints about frequent filter changes or maintenance intervals from either type of system. With proper advice—beyond the “wisdom” found online—homeowners generally have a good understanding of what to expect and when. If this were not the case, my inbox would certainly be flooded, or at least there would be negative feedback online regarding the way we advise and sell single-family houses.

Mycraft schrieb:

I prefer central systems if you have the space and options... but I am obviously primarily pro-ventilation... so better decentralized than nothing at all... because that is the totally wrong approach... at least in the era of plastic-bag houses...

Every system has—like everything in life—advantages and disadvantages; there is no magical, one-size-fits-all solution when it comes to ventilation. But I do agree with you on one point—it is better to have a decentralized system than none at all, if the external conditions don’t permit installing one type or the other.

You have chosen the central solution; that’s fine. However, your personal decision should not be used as a reason to negatively judge other systems based on assumptions.

Best regards, Bauexperte

Bauexperte schrieb:

You have chosen the central solution; good. However, your personal decision should not be used as a reason to unfairly criticize other systems based on assumptions.

Regards, Bauexperte

With this thread and the other one, I believe we have generally been able to clear up many guesses, assumptions, and prejudices (for me regarding central ventilation and for @Mycraft regarding decentralized ventilation). Therefore, I found the discussion, after some initial difficulties, to be good and helpful. All is well.

https://www.hausbau-forum.de/threads/ventilatoren-fuer-feuchtraeume-und-abluftdunstabzugshaube.9077/

Hi
When I asked about the necessary cleaning of our centralized ventilation system, I was told it isn’t needed. The supply air already has a filter, so the ducts stay clean. Each exhaust air intake also has its own filter, keeping the exhaust ducts clean as well. Therefore, only the covers, which are easily accessible, need to be cleaned. Maintenance technicians with long brushes, cameras, or similar equipment are not required.
We’ll see if that actually works in practice. If not, I can get the necessary equipment myself and take care of it—it’s not rocket science, just a matter of effort.