Is heating load calculation with desired temperatures necessary?

Hello.
I have very often read in the forum that a heat load calculation should definitely be carried out. This weekend we were at a building fair and I spoke with 3 leading gas heating manufacturers. Each of them said that a heat load calculation with room-specific desired temperatures is unnecessary for a gas heating system, because the capacity of the gas heater is always sufficient. According to the exhibitors, a heat load calculation is always done anyway, but with a room temperature for the bedroom of say 18 degrees and 21 degrees for the living room. This is regulated somewhere as a standard temperature. I then told them that we deviate a bit from the average person and want 22 degrees in the bedroom and also 23 degrees in the living room. The exhibitors told me that this was completely irrelevant. With a gas heating system, you can always achieve these temperatures. The heating curve just needs to be adjusted accordingly.

The pipe spacing of the underfloor heating itself would also be irrelevant. If one possibly plans to install a heat pump at some point, one should reduce the pipe spacing of the underfloor heating from, for example, 20cm to 10-15cm.

What do you think about this?

Basically, the manufacturers are right. The gas heating will always be sufficient.

But: The room-specific heating load calculation is essential for the design of the underfloor heating. Even a gas heating system is more efficient at a low flow temperature.
In addition, you have the option to switch to a heat pump.

Furthermore, (I believe I have heard) that high flow temperatures in underfloor heating can cause health problems.

The burners themselves already have enough power. In this respect, one can agree that no calculations are needed for the dimensioning of the burners. The other aspect is economical operation. And in this regard, the industry, apparently up to the manufacturer, consists of people stuck in the past who simply cannot do better. What a self-revelation.

The burners themselves already have enough power. In this respect, one can agree that no calculations are needed for the dimensioning of the burner. The other aspect is economic operation. And here the industry, apparently up to the manufacturer, consists of people stuck in the past who simply cannot do better. What a self-revelation.

Okay, I understand. The burners, the gas heating system itself can handle it, but other structural measures are also important to implement. I assume you mean, among other things, the installation spacing?!

...

Heating engineers like to skip the heat load calculation, especially for natural gas heating systems. They simply install the 20kW standard boiler in a 150 m² new building, it will definitely manage that, and that’s how it’s always been done. Heating engineers are "to blame" if at -15°C it doesn’t reach exactly 22° in all rooms while the bathtub is being filled at the same time. That’s why they always add 50-100% on top, and then it should be enough; the extra 200€ cost for the larger system doesn’t matter.

The fact that the unit then constantly cycles on and off and never runs at full load except for hot water generation, and after 3-5 years the burner needs to be replaced and the heat exchanger is clogged, is just considered "normal wear and tear."

Gas condensing boilers do have a wide modulation range (usually 20-100%), but the systems should also be selected so that this range is utilized and the boiler is not always stuck running at 20-40%. I recently had my heating system renewed and it was hard work convincing the plumber that with 140 m², triple glazing, 30 cm ceiling insulation between floors, and basement ceiling insulation I DO NOT need a 24 kW boiler. And ta-da, even at -15°C last week it got cozy warm in all rooms with the 16 kW boiler at 52°C flow temperature (without underfloor heating).

A reasonable heat load estimate for individual rooms should also be made based on the exterior wall areas and room size. Sure, you can get almost everything warm by adjusting the flow temperature combined with a gas boiler, but that’s not always possible with underfloor heating. The bottleneck here is always the most critical room—meaning the largest exterior surface-to-volume ratio and hydraulically furthest from the boiler. Here, the heating surface should be generously sized, which is decisive for the required flow temperature.