ᐅ Student Takes on Building a Ventilation System Himself

Introduction / Preface

Hello!
My name is Christian, and I am 27 years old. This year, I completed my bachelor’s degree in Energy and Environmental Engineering and am now pursuing a master’s in Renewable Energies. I am an enthusiastic DIYer, if you can still call it that with my own lathe, milling machine, welding equipment, and so on.

Recently, I became the "owner" of a single-family house and am currently renovating it. Being a self-proclaimed "tech geek," I want to equip the house with some nice gadgets. I’m doing the renovation myself, and so far, the work is progressing well. As part of the refurbishment, a central ventilation system with heat recovery is planned to be installed (or at least the ductwork pre-installed).

The planned system
The house has approximately 140m² (1507 ft²) of living space plus a full basement. My plan is to install a central system in the heating basement. This system will be completely self-built as a low-budget solution.

The ductwork
Supply air will be delivered to the bedroom and living room (which is combined with the dining area and open kitchen).
Exhaust air will be extracted from the shower bathroom in the basement and the bathroom with a bathtub upstairs.

Since I am still at the "shell construction" phase, I want to lay all necessary ducts now. Due to structural reasons, I plan to use DN70 HT pipes (drainage pipes) for both supply and exhaust ducts.

QUESTIONS
1. Is there any reason not to use HT pipes (wastewater pipes) for the air ducts?

2. The internal diameter of the pipes is 70mm (2.75 inches). At an air velocity of 2 m/s (6.6 ft/s) in the main duct, I achieve about 28 m³/h (16.5 cfm), which means approximately 14 m³/h (8.2 cfm) each for the living room and the bedroom. Will an air velocity of 2 m/s already cause noticeable airflow noise?

3. The system is intended to provide “supportive” ventilation. Do you think it’s feasible to achieve effective ventilation support with the 70mm diameter ducts?

4. The air must of course flow from the “supply air rooms” to the “exhaust air rooms.” In the living room, I plan to install a ventilation grille in the door for this purpose. However, I want to avoid this in the bedroom for noise reasons and to prevent shortcut airflow. I have heard about sound-insulated wall connectors but don’t really know where to get them. Does anyone have tips?

5. Does anyone with experience in this area feel like visiting my construction site (in 21217 Seevetal near Hamburg) to offer helpful advice? I’m diving into this project completely on my own and would really appreciate the chance to exchange experiences.

Many thanks in advance!!

Avoid HT pipes because they can release gases – and you don’t want to breathe that in, do you? Why don’t you buy the well-known blue flexible hoses? Just search for Selfio – they offer free planning for you. It’s not perfect, but better than what you’re doing now.

I can only agree with that... the well-known plastic ventilation ducts are affordable and aerodynamically optimal.

With HT pipes, every joint can create potential turbulence spots, which can then lead to increased noise levels.

For projects like this, I always wonder: why reinvent the wheel?

Nowadays, you don’t have to buy a complete system, but there are all kinds of ready-made components and assemblies from various manufacturers. So, you basically just need to find or adapt the right parts instead of using something completely unsuitable.

Thank you in advance for the responses. The HT pipe will only be used as the exhaust duct... to put it simply... outgassing doesn’t really concern me in this case^^ Thanks anyway for the advice.
The supply air is supposed to be routed through a flue in the chimney. This flue is empty and has never been used. Are there any concerns about using a masonry duct for the supply air?

Regarding noise issues with HT pipes: Do you really think they generate more noise than a corrugated plastic flexible duct? Every ridged surface creates turbulence. In comparison, an HT pipe is quite smooth, isn’t it?

I don’t want to reinvent the wheel… but I want to do as much of the work myself as possible. Of course, I could just buy and install a complete system for $3000, but that’s a few thousand dollars too much for me... plus, I enjoy the challenge of figuring it out myself.
The systems shown all have a minimum airflow of 180 m³/h (106 cubic feet per minute). Why are such large airflow volumes necessary? I’ll never be able to accommodate that through my supply and exhaust ducts.

The flexible duct is naturally not ribbed on the inside. And for 3,000 euros, you won’t get a complete system….

I also install these myself and pay just under 7,000 euros instead of 12-15 thousand euros – and it has a maximum capacity of 500 m³/h (295 CFM). You should definitely have the whole system professionally planned – at least to avoid short circuits and to correctly calculate the airflow. This also prevents noise issues inside the house.

Have you also considered sound transmission between rooms? Why don’t you leave a gap at the bottom of the door leaves instead of planning unattractive grilles? Or what about a door frame ventilation that can be built neatly and discreetly yourself?

The telephone noise is the 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 beneath the door panel is, of course, possible, but I thought that this gap actually increases the telephone noise?

Another issue is the bathroom. When you come out of the shower, you are standing in front of the door... if air flows underneath through a gap, that would probably be uncomfortable with wet feet, right?

For these reasons, I was thinking about wall penetrations equipped with sound insulation. I checked Selfio and saw that the simple metal box (overflow element) there alone costs 150€ and there is no information about soundproofing! EDIT: Ah... it is mentioned in the PDF datasheet then...