ᐅ Central Ventilation System – Air Outlet in the Floor or Ceiling?

Hello home construction enthusiasts,

In a scope of work description, it states: "The supply air is provided through floor-level supply outlets with white cover grilles, for example in the living room, master bedroom, and children's rooms (if such rooms exist). By combining supply and exhaust rooms, the hallway is used as a transfer area. This means that the room doors have a gap of about 1 cm (0.4 inches) above the finished floor."

My question is: Do these floor-level supply outlets make sense? Is this meant to reduce drafts from above? I suspect that the solid construction company uses this as a standard because the ducts are installed in the floor (with impact sound insulation and heating inside) rather than suspending the ceiling.

Personally, I would prefer supply AND exhaust air in the ceiling (this seems more sensible to me, since if the air comes from below, furniture like cabinets could block it). But if both supply and exhaust are to come from the ceiling, wouldn’t you need to drill a hole through the intermediate ceiling (if you want the outlet on the ceiling in the ground and upper floors) or the basement ceiling (if you want the outlet on the ceiling in the basement)?

Thank you very much for your advice.

This interesting topic was not continued in the other thread:

schaaaf schrieb:

I don’t like to revive old topics, but I would like to hear arguments why the floor is preferred? Does this apply to both supply and exhaust air? Against floor outlets would speak the "suction" of dust and the stirring up of dust and the issue of furniture.

Source: https://www.hausbau-forum.de/threads/kwl-planung-position-der-komponenten-laenge-der-leitungen.39567/post-529840

Shiny86 schrieb:

My concerns about floor valves were in case something is spilled. But maybe that is rather unlikely. If vacuuming is enough for cleaning, then great. I didn’t know I was allowed to put something on top of the floor valves. For example, in the bedroom I could imagine a chair where clothes might be placed sometime.
So would you leave all positions as they are?
In the living room, I would move it though. Otherwise, there might be a draft when sitting on the sofa right above.
Suspending the ceiling on the upper floor is not an option for me. Can floor outlets also be installed in the dining room and living room? Then a sofa with legs can be placed there. I need a sofa with legs anyway for my robot vacuum cleaner.
And in the kitchen, maybe a wall outlet? Or does one have to have the same type of outlet throughout a single floor?

Source: https://www.hausbau-forum.de/threads/kwl-positionierung-der-zu-und-abluft-in-meinen-entwuerfen.36750/post-440380

One addition: The issue with drafts has already been discussed here. https://www.hausbau-forum.de/threads/kwl-positionierung-der-zu-und-abluft-in-meinen-entwuerfen.36750/post-441338. So this part of the question is already answered.
Cabinets and furniture should not pose a problem for floor vents; this has also been clarified in one of the earlier threads.

What I am still wondering is: Are wall outlet vents used in solid construction? Where would the duct be routed then?

And: What about the 1cm (0.4 inch) door gap? Is that a sound issue? Dust can get through there as well...

We once saw this offered by a prefab house builder and inquired about it. It was simply a way to simplify the construction process: The mechanical ventilation ducts are installed in the ground floor ceiling, with ceiling outlets on the ground floor and floor outlets on the upper floor.

It makes sense to always place the exhaust vent at the top because warm, moist air rises wherever it occurs (shower/bathroom, kitchen – even in a small toilet/guest WC when sitting and sweating *g*). You want to remove the humidity from the room.

And what about the basement? Is the ventilation typically installed in the ceiling or floor? If you have underfloor heating, it’s probably installed in the floor, right?

Hello,
in our house, the exhaust vent on the upper floor bathroom was installed within a wall. A small section of drywall was used to route the gas boiler’s exhaust pipe up to the roof and to accommodate the ventilation exhaust duct behind it.

Side effect:
Since this drywall section is right next to our shower, we had a small recessed shelf built into it for shower supplies.

On the upper floor, our fresh air inlets are also installed in the floor of the other rooms.

Regards,
Michael

Normally, the pipes for the mechanical ventilation with heat recovery are not installed on top of the raw floor slab, as is the case with underfloor heating, but rather within the raw floor structure. This is not the reason why the outlets are installed in the floor.

Basically, it always depends on how cleverly the ductwork can be laid. The shorter the ducts, the lower the resistance and the less noise is generated by the airflow. Therefore, it can make sense to route the mechanical ventilation ducts into the floor if this saves several meters of duct length. Wall outlets are also an option but require a certain minimum wall thickness. Regarding exhaust air, I agree with you to some extent, since exhaust vents are usually located in rooms such as bathrooms. Here, I would definitely prefer a ceiling outlet, because water can sometimes collect on the bathroom floor, and depending on the placement of the outlet, this water could enter the mechanical ventilation system.

As an alternative to the gap under the door, there are flat door seals that allow air exchange when the door is closed (transfer grilles). Be aware, however, these only permit a certain airflow in cubic meters per hour (m³/h); the rest has to pass underneath the door. Alternatively, transfer vents can be installed in the door frame. These, however, are disproportionately expensive if professionally installed.