ᐅ Design of Underfloor Heating for a KfW 55 Energy-Efficient House with a Ventilation System

Dear users,

I am a bit overwhelmed with whether our underfloor heating is being planned correctly. The house is still in the shell stage. I have requested the installation plans and heat load calculations from the general contractor. The heat load was calculated according to DIN EN 12831. I have this calculation and the results from the planning office.
The pipe spacing is mostly 18cm (7 inches), except in the bathrooms (once 6cm (2.5 inches), once 12cm (5 inches)) and the utility room (24cm (9.5 inches)). What unsettles me more is the fact that in both bathrooms an undercoverage of the heat load is stated ("missing heat ...kW"). Additional heating devices are not planned there so far.
May I post the planning documents if I redact personal information and the data of the planning office?

Best regards

dream2023 schrieb:

What concerns me more, however, is the fact that in both bathrooms an underestimation of the heating load is indicated ("heating shortfall ... kW"). Additional heating devices are not planned there so far.
May I post the planning documents if I redact personal data and the planning office’s information?

Best regards

It’s similar in our case. According to the calculation, we would also need to install a towel radiator on the wall, and in our bathroom the spacing is absolutely fine. This is because we have no loops under the shower and the bathroom is rather small, resulting in a limited floor area.

HnghusBY schrieb:

It’s similar for us. According to the calculation, we would also need to install a towel radiator on the wall, and in our bathroom, the spacing is absolutely fine. This is because we don’t have loops under the shower, and the bathroom is rather small, so there is little floor area.

So, would that be acceptable, or could it be optimized further, for example by slightly extending the pipe length?

Attached is the planning.

Having an underfloor covering in the bathroom and laying only 12cm (5 inches) pipe spacing is obviously not ideal. Also, a very long heating circuit doesn't make much sense. It’s better to have more shorter circuits rather than fewer longer ones. Are you fixed on using the studded panel system? With a stapled installation, a closer pipe spacing should be possible.

Overall, I find the spacing quite large. Are there not possibilities to use more surface area in the bathroom and then achieve a lower supply temperature with smaller pipe spacing? Do you know what minimum temperature was assumed?

Good morning,

Thank you for your response. So, the outside temperature mentioned in the assumptions was -11°C (12°F), and most calculations were done using an adjacent temperature of -9°C (16°F). Is this what you meant?
Are you referring to the very long pipe in the living-dining area? I thought the pipe length here referred to the total length for both circuits there.

Could it be that 12 cm (5 inches) is planned above in the bathroom because the distribution box is located there, which generates some additional heat or reduces available space? In principle, it might be possible to reduce this to at least 6 cm (2.5 inches) at the top. Downstairs, 6 cm (2.5 inches) is the minimum possible.

I’m not sure if we have to stick with the studded membrane system. I will arrange an appointment with the heating specialist and first ask for possible solutions. But honestly, I have no idea how to argue this.

dream2023 schrieb:

So, the outside temperature mentioned above in the assumptions was -11°C (12°F), and calculations were mostly done using an adjacent temperature of -9°C (16°F). Did you mean these figures?
Are you referring to the very long pipe in the living-dining room? I thought the pipe length here referred to the total length for both circuits there.

Yes, I meant those figures. That sounds correct. Here and occasionally elsewhere in the forum, calculations were still based on the old standard, which assumed colder outside temperatures. You are right about the pipe length; I missed that on my phone.

dream2023 schrieb:

Could it possibly be that 12 cm (5 inches) is planned in the bathroom above because the manifold is located there, which generates additional heat or reduces available space?

That doesn’t seem plausible to me. Having the heating circuit manifold in the bathroom certainly makes sense to provide additional heat input there, but it doesn’t reduce the pipe spacing. Ultimately, the main bathroom is usually the most critical room (small area, high temperature). Simply put: the more heat input is possible in this room, the lower the required supply water temperature of the underfloor heating can be, which makes the heating system run more efficiently (I am assuming a heat pump). Solar heat gains, the heating circuit manifold, occupants, etc., are not factored in here. Therefore, I find some degree of underheating in the bathroom acceptable.

dream2023 schrieb:

I’ll arrange an appointment with the heating engineer and ask him for solution proposals first.

To get a solution proposal, you first need to define a problem. Just ask about the available adjustment options to improve the heating system. Was the design done by the heating engineer or the planner? In our case, the heating engineer installed the underfloor heating completely differently because he thought the original design was outdated (tighter pipe spacing, more heating circuits, narrower spacing in front of window fronts). I also can’t imagine a heating engineer would use a pipe spacing of 12 cm (5 inches) in the main bathroom.

Please note that I don’t yet live in the house, so my comments are rather theoretical. Whether what has been installed actually works well for me, I still have to find out. 😉