Heating load calculation or room heating load

The response was: "yes, heating load DIN EN 12831, is calculated by our system technician." Is that now the room-by-room calculation or something general that concerns the entire house? It is a prefabricated house, but the floor plan is individual for us, therefore "unique."

Is there a general statement about this? I would write in my contract, "Design and installation of underfloor heating at a flow temperature of 30°C according to room-by-room heating load calculation in accordance with DIN 12831."

That should be sufficient, right?

Unfortunately, nothing is contractually mentioned in this regard. Neither in the contract with the prefab house company nor in the "contract" with the sanitary company. It is only described that I receive an air-to-water heat pump with integrated controlled residential ventilation (upon request, as mentioned Tecalor 5.5 eco) with underfloor heating. Can anyone make sense of this statement from the sanitary company, especially regarding the DIN? I specifically and proactively asked whether the heating load calculation is done room by room. Best regards

In general, prefabricated house companies are extremely rigid when it comes to external interventions in their planning.

Or to put it another way: You may be the builder and pay for the whole thing, but ultimately the heating installer is a subcontractor of the prefabricated house company and gets paid by them, and also wants to continue getting paid by the prefabricated house company in the future.

But asking doesn’t cost anything; maybe you’ll get lucky. You can only avoid the ERR with an exemption application, which must be submitted together with the building application.

In general, the heating installer will have the heating load and underfloor heating calculated/designed by an underfloor heating manufacturer. It was the same for me; I then received a summary of the heating load and the design of the underfloor heating. Upon request, I got the detailed printout with individual rooms.

Based on the heating load, Tecalor/Stiebel Eltron will recommend the size of the heat pump including the ventilation system. For the ventilation system, there will then also be a quick design according to DIN 1946 for controlled residential ventilation, and that’s it.

I would try to have the underfloor heating designed for a maximum 30°C supply temperature in NAT and as small a spacing as possible, 5 cm or max. 10 cm.

For the heating load, I would specify room temperatures of max. 21-22°C; you won’t get much larger temperature differences between individual rooms anyway.

If there is a towel radiator in the contract, then operate it electrically only, and do not connect it to the water circuit of the underfloor heating.

If complaints start that the heating load in the bathrooms at 24°C is not covered, argue that the underfloor heating is supposed to deliver 20°C at 30°C supply temperature and 5 cm or max. 10 cm spacing, and if you really want 24°C, you want to switch on the electric radiator.

And insist on the smallest possible heat pump and don’t let yourself be talked into buying the larger heat pump for the same money.

Just received an offer for a heating load calculation and the design of the underfloor heating. 2,000 euros net from a locally based planning office for technical building services...

Is my impression justified that this is way too expensive?


Do I understand you correctly that you would design all rooms within the insulation for 21-22 degrees, including the bathrooms? Why, or what is the technical reasoning behind not aiming for 24 degrees in the bathroom?

A heat pump should operate with a low supply temperature, therefore 30 degrees.

But that also means you need a lot of surface area for the underfloor heating [Fbz].

This surface area is not available in most bathrooms, so 24 degrees are not reached.

Solutions:
Increase supply temperature -> Leads to higher heat pump costs

Increase surface area through wall heating -> Additional costs and many heating installers do not want to do that.

Additional electric heating
Infrared mirror -> Additional costs but fast heating of the room and never fogged mirrors
Electric radiator -> Additional costs as well as slow heating and not effective.

I had my entire house designed for 20°C, am using the lowest heating curve available and still have 23-24°C everywhere (if I don't throttle the output via the ERR), partly due to various external heat gains. (And this does not mean the current outside temperatures with open windows) meaning that the heating load calculated by the average heating installer/wholesaler/underfloor heating manufacturer still has a lot of reserve.

For me, a heating load of just under 3.2 kW was calculated at minus 12°C outside temperature for 20°C inside. However, the external gains from solar radiation and the ventilation system were not taken into account, so my actual heating load is probably 2.5-2.8 kW.

Originally, the main contractor wanted to install a 5 kW heat pump under the motto, then you have reserve.

At my insistence, the 3 kW system was installed...

I have to say that so far I haven’t been able to carry out a proper adjustment because the system has not been in operation for very long.