I need advice on the cost of heating

Hello,
We want to build a city villa. According to the BT building description, it should be built with 17.5 calcium silicate brick and 14cm ETICS, hip roof with 22-degree pitch.
The room height should be 2.5m for 138m2 of living space.

According to the building description, a Vaillant AuroCompact with stratified storage tank (150l), underfloor heating on both floors with individual room control, and 2 solar modules (each 2.51m2) are to be installed.

Now we asked what additional cost would arise if we wanted a Kfw70 house.

The following offer was made to us.

Increase insulation from 14 to 16cm, heat pump air/air (manufacturer still unknown), and windows with triple glazing (previously Veka with double glazing with Ug 1.0) should cost €12,500. Is that justified? I find it a bit rather high, considering that the development costs for gas have already been offset.

Unfortunately, I do not know the heating load.

Regards
Kay

For an air-to-air heat pump, you really have to be convinced... It's best to check somewhere whether you really like it.

You can easily achieve KfW70 with a gas condensing/solar solution. If the construction company can't manage that without a heat pump, I would look elsewhere.

Instead of sticking even thicker plastic on the facade, I would rather make the rather slender 17.5 cm stone wider and possibly switch to something "more modern" like aerated concrete. With this, due to the good lambda values, you can achieve KfW55 or even KfW40 without [WDVS]!

Don't just pay attention to the UG value of windows, but also to the UF (frame) or directly to the UW (both combined). It should be triple glazing, however, and you can generally do without passive house windows with UG 0.5, unless you have pretty large window surfaces.

The following situation applies to us:

KfW55 new build without basement, 1.5 stories, knee wall 70cm, 112sqm living area, 4 floor-to-ceiling, 2 small and 5 normal windows
Roof orientation 30° West/60° South

Exterior wall 36.5cm aerated concrete:
0.2 W/m²K

Attic ceiling WLG030 and roof WLG030:
0.15 W/m²K

Floor slab perimeter insulation:
0.24 W/m²K

Front door with 6 glazed windows:
1.8 W/m²K

Triple-glazed windows (U-value for glass + frame)
1.06 W/m²K

Heat generator:
Gas condensing boiler: Viessmann Vitodens 300
System control: Vitotronic 200
Solar 5 sqm: Vitosol 200-F
Solar storage tank: Vitocell 100-W 300 liters

Technology:
Gas condensing boiler with solar for hot water
Underfloor heating in all rooms
Decentralized ventilation Lunos e² with 90,x% heat recovery

At a later point in a few decades, it is still possible to add thermal insulation to the facade to, for example, achieve a U-value from 0.2 down to 0.08. Also, the roof is prepared for photovoltaic installation; with good modules, a zero-energy house is possible.
The question is always whether it pays off... especially if you have to take out a loan to finance it and pay interest, it takes a long time for such investments to amortize. Such a thing currently costs an estimated 40,000 euros and therefore hardly pays off, with about 500 euros heating costs per year :)

Hello,

....Technology:
Gas condensing boiler with solar for hot water, underfloor heating in all rooms
Decentralized ventilation Lunos e² with 90,x% heat recovery

What is the approximate actual energy demand for heating and hot water that was determined and contractually agreed upon for this?

....The question is always whether it pays off... especially if you have to borrow the money and pay interest, it takes a long time for such investments to pay off. Something like this currently costs an estimated 40,000 euros and is therefore hardly worthwhile, with about 500 euros heating costs per year :)

Correct, however, only the inventor of this number probably knows how they arrived at 500 €/a ;-)

best regards

Increase insulation from 14 to 16cm, heat pump air/air (manufacturer still unknown) and windows to triple glazing (previously Veka with double glazing with Ug 1.0) should cost €12,500. Is that justified? I find that a bit really high, considering that the connection costs for gas have already been offset.

Why too high? That’s a realistic price... however, I would skip the air/air nonsense and stick with gas... but anyone who can’t build a KfW-70 house with gas should look for their customers elsewhere...

Hello,

You really have to be convinced of an air-to-air heat pump...

That's true, furthermore it makes no sense in the presented combination

You can easily achieve KfW70 with a gas condensing boiler/solar solution.

If you assume a "typical" gas condensing boiler/solar system, this is a bold statement; it crucially depends on the house's location relative to the sun. Theoretically it is possible, but in practice rather very rare. Often additional measures have to be taken.

Rhenish regards