ᐅ New Construction: Floor Structure / Ceiling Thickness for Ductwork of Mechanical Ventilation Systems

Good evening,

we are building a house (currently in the preliminary design phase) and I am currently sorting out an issue between the architect (who has never installed a mechanical ventilation system with heat recovery but is otherwise excellent) and the heating engineer. I have a question about the floor construction with mechanical ventilation:

As I understood from the heating engineer, there are three options:

Option 1: With a 20cm (8 inch) concrete slab, the 63mm (2.5 inch) duct is completely embedded within the concrete slab. On top of that comes a 15cm (6 inch) floor build-up as planned by the architect, including impact sound insulation, underfloor heating, etc.

Option 2: Concrete slab (20cm / 8 inch), and then within the 20cm (8 inch) space above it (instead of the 15cm / 6 inch build-up as planned), the 63mm (2.5 inch) ducts plus underfloor heating and other layers.

Option 3: Too expensive because of shallow ducts, so not an option.

Or are options 1 and 2 actually the same, meaning I definitely need a 20cm (8 inch) concrete slab plus a 20cm (8 inch) floor build-up?

Additional question/comment: At the end of the day, because the ground floor has large rooms, it makes sense to increase the story height (floor to floor level) by 275cm (108 inches) to be on the safe side...

Thank you very much

Option 1 is probably the most common method. Just make sure there is enough overlap and, if necessary, add some extra reinforcement.

Option 2 is also possible, but it requires sufficient ceiling height.

Option 3 is, in my opinion, the most elegant solution, but it is more expensive.

There is also option 4, where the ceiling is suspended, and option 5, where everything is distributed over the attic space (insulated in this case).

Do you have two reinforced concrete slabs or just one?
It might be necessary to combine variants, for example V1 for ventilation on the ground floor and V3 for the upper floor.
75mm (3 inches) pipes are better than 63mm (2.5 inches). The flexible pipes also come flat, so with proper planning, variant V3 is hardly more expensive than variant 2.

With proper planning, rectangular metal ducts can sometimes be more cost-effective, as many components such as large air distributors are no longer needed.

Mycraft schrieb:

With proper planning, flat ducts (sheet metal) can sometimes even be more cost-effective, since many components like large air distributors are no longer needed.

Sorry, I don’t want to hijack the thread, but I just need to ask quickly—maybe this will also help the original poster.

Honestly, I haven’t dealt much with our ventilation system technically because I feel well taken care of by our provider.

We don’t have flat ducts; instead, we installed round flexible ducts in the concrete ceiling. But I keep reading here about air distributors that need to be installed in the ceilings, etc. There was even a thread where they were curiously installed in the floor structure.

I’m 99% sure we don’t have any air distributors in the ceiling. I’m just a bit confused because it sounds like, from what you say, that you can only avoid using air distributors if you have flat ducts!?

For round flexible ducts, the manifolds are usually located under the ceiling or on the wall—where the ducts come out.