ᐅ Design of Underfloor Heating – Legal Requirements

Good evening, dear house building experts!

We are currently planning the construction of a house with a building company (prefabricated house provider), with construction starting in 2024. The detailed design is still pending. So far, we have not received a clear statement from the builder regarding the design of the underfloor heating system. There was mention of a flow temperature of "about 35°C (95°F)." The performance specification only states that the heating system will be executed according to the applicable technical regulations (aRdT). Of course, we want the underfloor heating to be designed as efficiently as possible. We hope that the builder is willing to discuss and agree on a straightforward design. Nevertheless, we would like to know what we are entitled to and where we depend on the builder’s willingness to accommodate us.

• How much freedom does the builder have in determining the flow temperature? We have read that DIN EN 1264 specifies a maximum flow temperature of 35°C (95°F) and a temperature difference of at least 5 K. Is this correct, and is this DIN standard part of the applicable technical regulations (aRdT) or otherwise binding for the builder?
We would prefer a lower value if possible. We could not find any other DIN requirements regarding the flow temperature. Are there any others?

• We would like to be involved early in the planning and heating load calculation. According to what we have read, § 650n grants a right to obtain the room-by-room heating load calculation from the builder. Have we understood this correctly?
• DIN EN 12831 allows the setting of indoor temperatures according to the standard or by agreement (form V). Can the builder simply set the temperatures according to the standard, or must the owner be asked whether individual temperature settings are desired?
• If we have understood correctly, the owner can demand the desired design of the underfloor heating according to § 650b of the Building Code. The builder may then charge the additional costs. Is that correct?

The only mandatory requirement is a 35°C (95°F) supply temperature and minimum temperatures of 20°C (68°F) in the living areas, up to 24°C (75°F) in the bathroom. Everything else depends on how accommodating your builder is and how large your budget is.

Let me put it this way: if you plan for updates from the start and are not satisfied with just the basic standards, such as work according to DIN or technical regulations, then a general contractor (GC) or a “prefabricated house supplier” (whatever that means) is not the right choice. In that case, you should hire an architect and build the house together with them.
P.S. A construction company does not set the standards. They are only responsible for ensuring that the standard or DIN has been applied.

Thank you for the feedback.

WilderSueden schrieb:

Everything else depends on how nice your builder is

Is that really the case? See question 4.

ypg schrieb:

I’ll put it this way: if you plan for updates in advance and don’t settle for the basic standards, like work according to DIN or technical regulations, then a general contractor or “prefabricated house provider” (whatever that means) is the wrong choice.

Maybe in hindsight, but we are already committed to the company. And whether that is actually true is what I want to find out in this thread, see question 4.

A supplier is not obligated to fulfill every request made by the customer. Ask your representative how such change requests are handled.

WilderSueden schrieb:

The only mandatory requirement is a 35-degree supply temperature and minimum room temperatures of 20 degrees in living areas, up to 24 degrees in the bathroom.

Is that really the case? I’m familiar with the 20/24 degrees, but the fixed 35-degree supply temperature is new to me.

HausbauFrage schrieb:

We would like to be involved early in the planning / heating load calculation.

I wouldn’t expect to find this in any legal regulations. This topic is important to you in terms of efficiency and comfort, but for the builder it’s usually just an inconvenience they want to handle as cheaply as possible. Make sure you address this very early on and insist strongly that it gets optimized. If necessary, have your own calculations done and try to enforce them. In the end, it’s mostly about laying some pipes closer together, adding a few more heating circuits, and in the worst case installing a larger manifold and using an additional wall in the bathroom. The first three points are usually of little concern to the contractor; the last point is probably the most effective but also the most difficult to implement. Yes, there will be some extra costs, but I don’t think anyone should push back too hard on that.

And don’t get too caught up in the actual calculation. I’d generalize by saying that for most prefab home suppliers, a heating load calculation is just a document that has to be produced at some point, but not much thought goes into it otherwise.