Is the heating dimensioning sufficient?

Hello everyone,

we are about to decide which offer from the heating engineer to choose! As always, the offers and dimensioning are very diverse!!!

A few facts:

Annual primary energy demand targeted at 42.5 kWh/m²a (according to current calculation) 31.5% better than new build The house will have about 240m² heated rooms, including bedrooms, dressing rooms, corridors, party cellar (which will only be fully heated at certain times) that will certainly not be heated that much. In addition to the 240m², there are about 60m² of basement.

Currently, there are 2 of us planned, but the maximum is 4 people living in the house :)

The most attractive offer looks like this: a Vaillant flexoCOMPAKT VWF 88/4 was offered with 8.9 KW, 185 L domestic hot water storage and 50L buffer storage.

In stark contrast, I have received an offer for a Buderus with over 13 KW + 390L domestic hot water + 300 L buffer.

We have a "normal" showering behavior and rarely bathe, so very large, very hot water quantities are rather unlikely.

Every opinion counts, the contract is to be awarded on Friday.

We have the 55/4 - so 5.3 kW and as far as it goes for 190 sqm kfw55... the annual primary energy demand - especially with heat pumps - is actually a very poor value for sizing the heating system... You need a heat load calculation - without it everything is guesswork. I would leave out the buffer tank - or is it for hot water?

We have the 55/4 - so 5.3 kW and so far it is suitable for 190 sqm kfw55... but the annual primary energy demand - especially with heat pumps - is a really poor value for dimensioning the heating...
You need a heat load calculation - without that everything is guesswork.
I would omit the buffer storage - or is it for hot water?

The provider of Vaillant will have a heat load calculation carried out after the order is placed. It is guaranteed in the order that if the offered system is too small, the next larger one will be installed at the same price.... What about the storages? Is 50l heating and 185l hot water enough?

I wouldn't do a hot water tank at all. Hot water has been sufficient for us so far - but we'll see how it goes when the children shower every day.

The heating storage tank is mandatory and is not a normal buffer in the supply line, but for the return line - to have a buffer when all thermostats are turned off at once. There are various system diagrams that represent this. For me, 185l is too little - we have almost 400l. We also like to shower hot and long...

Interesting. Of course, we don't have that :D although we also don't have any thermostats.