ᐅ Planning and Design of a Mechanical Ventilation System with Heat Recovery – Maximum Duct Lengths

Hello everyone,

maybe I don’t actually need to post this question in the telecom-themed forum (and register there as well...).

We are currently planning the (major) renovation of a 1960s house, and the installation of a controlled residential ventilation system is under consideration. While the overall planning is being done by an architect, the ventilation issue has turned out to be a bit more complicated. The HVAC company has the ventilation system planned by a wholesaler (it concerns a Pichler LG350), and communication has been difficult there (openings face the neighboring terraced house, etc.).

Before we either fire the company or ditch the ventilation system altogether (or just have the HVAC contractor handle heating and plumbing), I wanted to clarify a fundamental point here:

- In the "ventilation plan" (created using a variant of airPLAN software, which apparently circulates in various freeware versions) it says: Maximum length between manifold and supply diffuser: 15 m (50 feet).

Question: Does anyone know if this is correct? Is this completely independent of the device? This number also appeared in my "test draft," which I created with the above-mentioned software entirely without devices.

With a potentially "old-building-compliant" installation in the attic (and corresponding ductwork), we would definitely exceed the 15 m (50 feet) duct length.

At the moment, we are leaning towards giving up on the system and ventilating minimally with decentralized units (e.g., in utility rooms)...

Christoph

Is this a single-family house that you want to renovate?
What are its dimensions? Do you want to install the mechanical ventilation system in the basement?
I ask because, normally, it should fit within 15 meters (50 feet) in a "typical" single-family house, right?
I’m not sure if there are actually any length limitations.

This is an end-of-terrace house located in the city center, with a basement, ground floor, first floor, and attic (~200m² (2153 sqft)).

It should be noted that a mechanical ventilation system with heat recovery is not a must-have for us – we recognize the comfort benefits and likely the contribution to moisture control, but it’s not absolutely necessary.

The energy consultant’s initial plan was to install the system in the basement and run the pipes along the exterior wall (under the insulation). However, the manufacturer does not consider this ideal (and the costs were relatively high; the installer was also reluctant to commit due to the extensive channelling work involved).

During our discussions, we then considered the option of placing the system itself in the attic and distributing the ducts from there. In that case, the ducts would need to be routed both vertically (attic to ground floor ~5.3m (17.4 ft)) and horizontally along the walls (at least ~15m (49 ft)).

Is it the case that from the central unit, one duct runs to each individual outlet? In other words, is the number of ducts equal to the number of supply/exhaust vents?

Attached is the mentioned "duct layout plan".

caddar schrieb:
There, the pipes would have to be distributed not only vertically (attic -> ground floor approx. 5.3 m (17.4 ft)), but

Is there a misunderstanding on your part?
Place the unit in the center of the distribution board. The height to the ground floor ceiling is 5.3 meters (17.4 ft). If the single-family house were 12 meters (39.4 ft) long, you would need roughly another 6 meters (19.7 ft) just as a rough estimate, putting you at the short exterior wall. But you don’t have to, since it’s enough if the valve is located in the interior wall. With a room width of 3 meters (9.8 ft), you would need a maximum of 8 to 9 meters (26.2 to 29.5 ft) for the longest pipe run.

Oh, my attic would now be your inhabited top floor. That is my mistake. Still, everything should fit within <= 15 meters (49 feet).

I realize another mistake on my part: you don’t have a shaft to install the pipes 🙁

No, the attic is finished, meaning that placing equipment in the center and/or arbitrary distribution is unfortunately not possible. Since it is an older building anyway, we are trying to stick as much as possible to the installation shafts (for the attic-to-ground floor route) and drilling at the "corners."

EDIT: Although if I were to run the cables along a shaft under the roof, I might actually get closer to your values. Hold on, I’ll upload something...