ᐅ Is a recirculation line necessary? The 3-liter rule appears to have been exceeded.
Created on: 30 Nov 2025 21:09
S
Scash93Hello everyone,
We are currently building a prefabricated house with a major manufacturer and are actually at the point where we should be informed about the installation date. This means all documents have already been finalized and approved, and according to the builder, no further changes are possible.
However, the builder has now unexpectedly contacted us to say that a circulation pipe is mandatory on the upper floor, as the 3-liter rule allegedly cannot be met. During the selection process, we already signed off that we do not want such a pipe.
The bathroom on the upper floor is located almost directly above the utility room (a section of the floor plan is attached). Although I am not an expert, my own research suggests that a circulation pipe would be rather unusual with this pipe layout. We still do not want a circulation pipe.
We have already had problems with the builder, and the tone has always been “if you don’t agree to the extra costs, construction will stop.” We expect this again in this case.
Are there any experts here who can support us or give an assessment of whether a circulation pipe is really necessary?
Best regards
Scash
We are currently building a prefabricated house with a major manufacturer and are actually at the point where we should be informed about the installation date. This means all documents have already been finalized and approved, and according to the builder, no further changes are possible.
However, the builder has now unexpectedly contacted us to say that a circulation pipe is mandatory on the upper floor, as the 3-liter rule allegedly cannot be met. During the selection process, we already signed off that we do not want such a pipe.
The bathroom on the upper floor is located almost directly above the utility room (a section of the floor plan is attached). Although I am not an expert, my own research suggests that a circulation pipe would be rather unusual with this pipe layout. We still do not want a circulation pipe.
We have already had problems with the builder, and the tone has always been “if you don’t agree to the extra costs, construction will stop.” We expect this again in this case.
Are there any experts here who can support us or give an assessment of whether a circulation pipe is really necessary?
Best regards
Scash
Hi Scash,
The 3-liter rule means that in a building’s hot water pipes, the amount of water wasted after opening a tap should not exceed 3 liters (0.8 gallons) before hot water arrives. Usually, this is achieved by keeping the pipe run as short and direct as possible to the fixture to avoid unnecessary water waste. If your bathroom is located almost directly above the utility room, there is actually good reason to believe that a circulation pipe might not be strictly necessary.
However, there is an exception if the pipe run is particularly long or if the water pressure is insufficient to deliver hot water quickly enough to the fixture. In such cases, a circulation system may be needed to ensure hot water is always immediately available. But if the distance from the utility room to the bathroom is really short, it could be that the builder is simply playing it safe—perhaps due to internal regulations or liability concerns.
Have you asked for the exact pipe length or consulted another expert who could inspect the situation on-site? In principle, you could insist on not having a circulation pipe, especially if the 3-liter rule can be met without one.
Good luck!
The 3-liter rule means that in a building’s hot water pipes, the amount of water wasted after opening a tap should not exceed 3 liters (0.8 gallons) before hot water arrives. Usually, this is achieved by keeping the pipe run as short and direct as possible to the fixture to avoid unnecessary water waste. If your bathroom is located almost directly above the utility room, there is actually good reason to believe that a circulation pipe might not be strictly necessary.
However, there is an exception if the pipe run is particularly long or if the water pressure is insufficient to deliver hot water quickly enough to the fixture. In such cases, a circulation system may be needed to ensure hot water is always immediately available. But if the distance from the utility room to the bathroom is really short, it could be that the builder is simply playing it safe—perhaps due to internal regulations or liability concerns.
Have you asked for the exact pipe length or consulted another expert who could inspect the situation on-site? In principle, you could insist on not having a circulation pipe, especially if the 3-liter rule can be met without one.
Good luck!
Hi Nauer,
thank you for your reply.
It’s a bit unclear to us, as the distance to the bathroom on the upper floor is actually quite short. For a 16x2 pipe, you would need about 27 meters (89 feet) to reach those 3 liters.
We have requested the plans. However, we assume that the construction company will not provide them easily. That’s why we are now looking for some support 🙂
Best regards
Scash
thank you for your reply.
It’s a bit unclear to us, as the distance to the bathroom on the upper floor is actually quite short. For a 16x2 pipe, you would need about 27 meters (89 feet) to reach those 3 liters.
We have requested the plans. However, we assume that the construction company will not provide them easily. That’s why we are now looking for some support 🙂
Best regards
Scash
In the setup where the utility room is located directly below the bathroom, having a circulation pipe is really hard to justify... To exceed the 3-liter limit, they would practically have to lay the pipe in a zigzag pattern 😀 Without a clear length calculation, this sounds more like an assumption than a technical fact. Ask specifically how many meters (feet) they supposedly need and why this routing is necessary at all. If no precise figure is provided, the issue almost explains itself.
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