ᐅ Proper Piping System & Appropriate Pipe Diameters for Plumbing?

Hello everyone,

For our renovation project, I plan to completely redo all the (pipe) installations. I have two questions in advance:

- For aluminum composite pipes, which system is better: crimping or compression fittings?
- What diameters are generally used for radiators and domestic hot water?

The layout will be:
Basement: Heating system in the basement, with only one cold water connection (washing machine separate, supplied with rainwater)
Ground floor: Kitchen with one sink (hot + cold) + dishwasher,
Bathroom with shower + washbasin (toilet is separate, supplied with rainwater),
5 radiators for 5 rooms, total 90m² (970 ft²)
Attic/Top floor: Bathroom with shower + washbasin (toilet is separate, supplied with rainwater),
4 radiators for 4 rooms, total 65m² (700 ft²)

Hello,

Unfortunately, it’s not that simple. To determine the pipes for the heating system, you need to know your heating demand, as the pipe diameter is chosen accordingly.

For water supply, it’s easier. The riser pipe is usually 32mm (1¼ inches) plastic pipe or 28mm (1⅛ inches) stainless steel pipe. The supply line inside the bathroom is typically 20mm (¾ inch) plastic pipe, then 16mm (⅝ inch). It’s best to create a ring layout so you can easily see the pipe diameters.

Regarding installation, I use Rehau with sliding sleeves. The advantage of this pipe is that the connectors do not reduce the pipe diameter. Alternatively, I also use Geberit Mepla, Mapress, and Sanipex (with screw fittings). You should be aware that press and sliding sleeve connections require special machines.

Alternatively, push-fit systems like Geberit Pushfit can be used; these don’t need special tools (except for the calibrator).

Tom1607 schrieb:
To determine the pipes for the heating system, you need to know your heat demand, and the pipe diameter is chosen accordingly.

Is this something a layperson can do, or are there general guidelines? Alternatively, we have an on-site appointment with an energy consultant for the KfW assessment coming up anyway, so presumably, they should be able to estimate that as well.

Tom1607 schrieb:
With water, it's simpler. Riser pipe 32mm (1¼ inch) plastic pipe or 28mm (1¼ inch) stainless steel pipe. Supply line 20mm (¾ inch) plastic pipe inside the bathroom, then 16mm (⅝ inch).

The terminology is new to me, but I assume:
- Riser pipe = main pipe running from the basement up to the floors
- Supply line = for each room (so one 20mm (¾ inch) line for the kitchen, one 20mm (¾ inch) per bathroom)
- 16mm (⅝ inch) for each fixture

I once read that smaller diameters are recommended for hot water (consistently 16mm (⅝ inch)) to get hot water faster.
That probably only works if no one is using water at the sink while someone is showering, right?

Tom1607 schrieb:
It’s best to create a ring circuit so that the pipe diameter can be chosen more easily.

Okay, that’s worth considering.
About 10 years ago, during the interior finishing of a prefab house, I remember the water supply per floor was arranged like this:
Supply line to the shower -> to the sink -> maybe to the kitchen sink. All the same diameter (I don’t know which), no ring circuit, no circulation pump.

Tom1607 schrieb:
Regarding installation.....

I was more thinking about whether both systems are 100% reliable and mature, or if one is better suited for long-term durability.
I assume that screw connections are primarily designed so they can be undone later, whereas press fittings are mainly intended for permanent installations, such as concealed or under screed.

Tom1607 schrieb:
You have to know that press and push-fit connections require special tools.

Yes, I’ve seen that, although there are also manual press pliers available.

Work on drinking water pipes should be carried out by a certified plumber and not by a social worker.
Apart from the fact that you are not allowed to perform this work, you would face serious problems in case of damage, as no insurance would cover it.
Your obvious lack of knowledge on the subject only emphasizes this...

This may sound harsh, but it needs to be said.
Attaching faucets yourself or installing a washbasin is more suitable for DIY projects.

Lumpi_LE schrieb:
Work on drinking water pipes should be carried out by a plumber and not by a social worker.[...] Your obvious lack of knowledge on the subject only emphasizes that....

Thank you for this helpful contribution to my question.
And that is exactly why I am here – to fill this gap in knowledge.
Would you like to contribute?

As I said, you are not allowed to do that, and no one can help you with it.

If a plumber came to you tomorrow and said he wants to teach a 10th-grade class in German and History starting next week and needs to quickly get the material that is currently being taught and how it is conveyed—what would you say to him?