New construction KFW55 house - heating design, different statements

Hello everyone,

I have been actively reading here for a few days now and have now decided to register today and present my current situation. My wife and I are currently planning our new build, the construction documents were submitted 6 weeks ago and we are waiting for approval.

The current plan is to build with an architect and not a general contractor, so there is free choice between the different heating and sanitary companies.

Key data about the house:
KFW55 standard
Flat roof, cubic design
Living area: 190 m² including 2.5 m² balcony, so the actual living area is 187.5 m². The basement has 60.67 m², of which 16.6 m² are included for technology. Therefore, I would like to heat 187.5 + 34.99 m² (basement excl. technology) = 222.5 m²
The thermal protection certificate is currently being calculated, but a first estimate has already been given regarding the required heating demand.

According to the KFW consultant & the first heating offer, a Viessmann Vitocal 200-S AWB-E AC D09 would be sufficient to heat adequately at 35 degrees flow temperature and achieve an annual performance factor >4.5 so that the subsidy applies. Now, of course, I have not only obtained one offer but several to get the best possible offer with the same performance scope, however, here I run into a "medium-sized" problem.

Statements from the companies:
Each of the heating & sanitary companies contacted gives different statements ......."Viessmann is great and we only work with that", "Ochsner is the best choice", "Weishaupt is the ultimate in quality" and "Heliotherm is the secret favorite among air-water heat pumps" and even worse, everyone finds their technical design the best.

Further statements from the heating and sanitary companies: The heating buffer "must be at least 300L", "a too large heating buffer is not good", "a fresh water station is absolutely necessary to prevent Legionella", "a fresh water station only makes sense in a multi-family house", "drinking water storage must be at least 300L", "you need an electric auxiliary heater in the bathroom", "an auxiliary heater is not necessary".

I am now more confused than at the beginning and don't even know what to believe anymore -_- but on one point most agreed and offered the air-water heat pump with similar performance data.

This question has certainly been asked 100 times and is not clearly answered, as every system has its advantages and disadvantages. But which manufacturer currently stands out and has systems with low failure rates or good service + high efficiency?

We would like to place the heating in front of the house and have also planned a suitable area, but it must comply with the necessary sound pressure limits for nighttime operation.

We have a total of 5 rooms on the ground floor (bathroom, office, living/dining, foyer & small pantry) here we would plan 6 or 7 heating circuits 1x bath, 1x office, 3x living/dining, 1 or 2x foyer including Sparkasse.
On the upper floor we have 7 rooms (hallway, child1, child2, bath2, utility room, parents' bath, parents' bedroom including dressing room), here we would plan one heating circuit per room.
In the basement, we have 4 rooms (hallway, storage 1, storage 2 and technology). Here we would plan 3 heating circuits as we will not heat the technology room.

Heating offers:
Weishaupt WWP LB 12-A R
Viessmann Vitocal 200-S AWB-E AC D09
Ochsner AIR Eagle 414 C11B G1-1
Heliotherm HP12L/10L-WEB depending on the final calculation

What is really necessary for the other components or the size of the storage tanks?
Hot water storage size?
Heating buffer size?
Fresh water station?
Laying distance of the underfloor heating? Bathroom 10? and other rooms 15?
Auxiliary heater in the bathroom? We want a heater there anyway because we always hang our towels there, so that is a minor issue for us.

Finally, it’s about costs... this concerns ONLY the heating including underfloor heating, insulation, and commissioning. The water pipes and drainage are NOT included.

1.) Weishaupt WWP LB 12-A R with 100L heating buffer, 300L hot water storage, no fresh water station, with circulation pump, including 3 electric wall heaters, air & sludge separator + insulation & underfloor heating 34,500 € net
2.) Offer company 1: Viessmann Vitocal 200-S AWB-E AC D09, VitoCell 100W 200L heating buffer, Vitocell 100W 300L hot water storage, no fresh water station, with circulation pump, including 3 electric wall heaters, sludge separator, no air separator + insulation & underfloor heating 29,300 € net
3.) Ochsner AIR Eagle 414 C11B G1-1, Ochsner 320L hot water storage, separate storage PU200 200L, no fresh water station, with circulation pump, including 3 electric wall heaters, sludge separator, no air separator + insulation & underfloor heating 38,300 € net
4.) Offer company 2: Viessmann Vitocal 200-S AWB-E AC D09, VitoCell 120E with 350L hot water storage & 250L heating buffer, VitoTrans 353 fresh water station, with circulation pump, without 3 electric wall heaters, Viessmann sludge separator & air separator + insulation & underfloor heating 29,800 € net
5.) Heliotherm is still pending.

I would be happy if I could get tips and tricks from you about what is really necessary to heat our house because I no longer see the forest for the trees... the prices also vary greatly...

Thank you very much and have a nice Nikolaus weekend!
Greetings from Hesse =)

Ochsner would be my last choice

What is really necessary for the other components or the size of the storage tanks?

Hot water storage size? 300L more is not necessary for a family of 4 in a single-family house of this size.

Heating buffer size? Since heat pump and underfloor heating -> no buffer.

Fresh water station? A matter of belief, if you have the money then yes, otherwise not.

Installation spacing of the underfloor heating? Bathroom 10? and other rooms 15? Additional heating in the bathroom? The installation spacings are not to be chosen rigidly according to any preferences or "That's how we always do it." But according to the transmission heat losses and the intended use of the rooms. Also, the glazing and the fixtures/fixed furniture play a role here. Especially have the bathroom(s) calculated very precisely and cover every m2, and if necessary provide partial wall heating. If you still want a towel radiator, it would be worth considering running it electrically since the use would most likely be sporadic.

Which heat pump ultimately provides the energy is more or less secondary. It only needs to fit the house in terms of capacity. In other words, neither too weak nor oversized. Much more important is that the installer is familiar with the device and technology and that you don't become a test subject.

No matter what you do, do not take a heating buffer. No matter what anyone tells you, no, it is not needed.

Ochsner would not necessarily be my favorite either, due to moderate experiences my parents have had with Ochsner service when there are problems. With Waterkotte, I had bad experiences during the construction phase, which is why I ended up with AlphaInnotec at short notice, and that only because the new heating installer simply preferred to offer Alpha Innotec. My advice: do not impose any brand other than the installer's favorite, that won’t work.

I would focus the decision on which company can most credibly convince you that they will install the system so that as low a flow temperature as possible is achievable. This includes a good design and the willingness to use tight installation spacing according to the calculation.

In the end, you will benefit more from that than from a €2,000 saving on the offer now. Which device is actually installed is rather secondary, as long as the customer service is right. On paper, practically all current heat pumps are good; the "art" of the installer is primarily to operate them in their efficient working range. That is what distinguishes the good from the bad. It will certainly always be warm.

take the company around the corner with their favorite heating system, because the technicians are trained, knowledgeable, easily reachable in case of malfunctions, and as a company they want to maintain their good reputation. Show the other offers and you won’t be too expensive