Student dares - Self-built ventilation system

Introduction/ Foreword Hello! My name is Christian and I am 27 years young. This year I completed my Bachelor’s degree in Energy and Environmental Technology and am now studying for a Master’s in Renewable Energies. I am a gifted handyman, if you can still call it that with my own lathe/ milling machine/ welding equipment, etc. Recently, I became the "owner" of a single-family house and am in the process of renovating it. Since I am basically a "tech freak," I want to equip the house with some nice gadgets. I am doing the renovation myself and so far the work is progressing well. A central ventilation system with heat recovery is also to be installed during the renovation (or at least the pipes laid). The planned system The house has about 140m² of living space plus a full basement. My plan is to install a central system in the heating cellar. This system is to be built completely as a low-budget project by myself. The pipes Supply air will be brought into the bedroom and living room (with dining room and open-plan kitchen). Extract air will be sucked from the shower bathroom in the basement and the bathroom with bathtub upstairs. Since I am currently still in the "shell construction" phase, I want to lay all the necessary pipes now. Due to building technology reasons, I want to make supply and extract air pipes from DN70 HT pipes. QUESTIONS 1. Is there any objection to building the air ducts from HT pipes (wastewater pipes)? 2. The internal diameter of the pipes is 70mm. With an air velocity of 2 m/s in the main pipe, I achieve almost 28 m³/h, i.e. about 14 m³/h each for the living room and for the bedroom. Do these 2 m/s already cause flow noise? 3. The system is intended to serve as "support"... do you think I can achieve this ventilation support with the 70mm diameter? 4. The air must of course pass from the "supply air rooms" to the "extract air rooms." In the living room, I plan to install a ventilation grille in the door for this purpose. However, for reasons of noise and short-circuit airflow, I want to avoid this in the bedroom. I have heard of sound-insulating wall penetrations... but don’t really know where to get them... does anyone have tips? 5. Does anyone with experience in this area maybe feel like visiting me on my building site (in 21217 Seevetal near Hamburg) and giving me helpful tips? I am diving in completely cold with my project and would really appreciate an exchange of experience. Many thanks in advance!!

HT pipes not because they can emit gases - and you don’t want to breathe that in, do you? Why don’t you buy the well-known blue flexible hoses? Just google Selfio - they plan for you free of charge. Not ideal, but better than what you are doing now.

I can only agree... the well-known plastic ventilation ducts don't cost the earth and are optimal in terms of flow dynamics...

With HT, you also have potential turbulence points at every connection, which can then lead to increased noise development.

With such projects, I always ask myself: Why reinvent the wheel?

Nowadays, you don't necessarily have to buy a complete system, but there are all kinds of ready-made components and assemblies from various manufacturers... so you basically only have to find the right ones or adapt them appropriately and not use something totally unsuitable for it...

Thank you very much in advance for the answers. The HT pipe will only be the exhaust duct.... in short... off-gassing would probably be pretty irrelevant to me^^ Thanks anyway for the hint. The supply air is to be guided through a draft in the chimney. It stands empty and has never been used. Are there any concerns regarding the supply air duct made of masonry?

Regarding noise development with HT pipe. Do you really think there is more noise there than with a corrugated plastic flex pipe? That generates vortices at every stupid corrugation. In contrast, an HT pipe is quite smooth?!

I don't want to reinvent the wheel... but I want to build as much as possible myself. Of course, I could simply buy and install a complete system for 3000€. But that's a few thousand € too much for me ... and I lack the "inventive spirit."
The shown systems have a minimum of 180 m³/h, why are such large volume flows necessary? I will never get that through my supply/exhaust pipes.

The flexible pipe is of course not corrugated on the inside. And for 3,000 euros you don't get a finished system....

I also install those myself and pay just under 7,000 euros instead of 12-15 thousand euros - and it has a maximum of 500 m³/h. You should have the whole thing planned - at least to avoid short circuits and to have a correct air volume calculation. This also prevents you from having noise in the place...

Have you also thought about telephone noise between the rooms? Why don't you leave a gap at the bottom of the door leaves and instead plan ugly grilles? Or a frame ventilation that you can build yourself nicely & invisibly?

The telephone noise is question 4

Frame ventilation is not possible because the frames are already installed (were already installed), they are solid wood frames/doors, which I am reluctant to damage. A gap under the door leaf is of course possible, but I thought that this gap actually supports the telephone noise?

Another problem is the bathroom. When you come out of the shower, you stand in front of the door.... if air now draws through a slit at the bottom, that would surely be unpleasant on wet feet...?!

For these reasons, I was thinking of wall penetrations equipped with sound insulation. I have now looked at Selfio and seen that the stupid metal box alone (overflow element) costs €150 there.... and there is not even anything mentioned about sound insulation! EDIT: Ah... it is then mentioned in the PDF datasheet...