ᐅ I need advice regarding the costs of a heating system.

Hello,
We are planning to build an urban villa. According to the building description, it will be constructed with 17.5 cm (7 inches) calcium silicate bricks and a 14 cm (5.5 inches) external thermal insulation composite system (ETICS), with a hipped roof at a 22-degree pitch.
The ceiling height should be 2.5 m (8.2 ft) for the 138 m² (1,487 ft²) living area.

The heating system specified in the building description is a Vaillant AuroCompact with a stratified storage tank (150 liters (40 gallons)), underfloor heating on both floors with individual room controls, and 2 solar panels (each 2.51 m² (27 ft²)).

We have now inquired about the additional cost if we want to upgrade to a KfW 70 energy standard house.

The following offer was made to us:
Increase insulation thickness from 14 to 16 cm (5.5 to 6.3 inches), install an air-to-air heat pump heating system (manufacturer not yet specified), and upgrade windows to triple glazing (currently Veka with double glazing, Ug 1.0). The price is €12,500. Is this justified? I find it a bit high, especially considering that the gas connection costs have already been offset in the calculation.

Unfortunately, I don’t know the heating load.

Regards,
Kay

You really have to be convinced to go for an air-to-air heat pump... It’s best to see one in action somewhere to find out if you actually like it.

Reaching KfW70 is easily possible with a gas condensing boiler and solar solution. If the construction company can’t achieve this without a heat pump, I would consider looking elsewhere.

Instead of adding thicker plastic insulation on the facade, I would prefer to make the rather slim 17.5cm (7 inches) masonry wall thicker and possibly switch to something more "modern," like aerated concrete. Thanks to its good thermal conductivity values (Lambda), you can achieve KfW55 or even KfW40 standards without external wall insulation systems (EWIS / ETICS).

Don’t just pay attention to the Ug value of windows but also the Uf value (frame) or ideally the Uw value (overall). Triple glazing should be standard, but Passivhaus windows with a Ug of 0.5 can usually be skipped unless you have very large window areas.

Our situation is as follows:

KfW55 new build without a basement, 1.5 stories, knee wall 70cm (28 inches), 112m² (1,205 sq ft) living area, 4 floor-to-ceiling windows, 2 small and 5 standard windows
Roof orientation 30° west / 60° south

Exterior wall 36.5cm (14 inches) aerated concrete:
0.2 W/m²K

Attic ceiling insulation WLG 030 and roof insulation WLG 030:
0.15 W/m²K

Perimeter insulation under slab:
0.24 W/m²K

Front door with 6 glass panels:
1.8 W/m²K

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

Heat generator:
Gas condensing boiler: Viessmann Vitodens 300
System control: Vitotronic 200
Solar thermal 5m² (54 sq ft): Vitosol 200-F
Solar storage tank: Vitocell 100-W 300 liters (79 gallons)

Technical details:
Gas condensing boiler with solar thermal for domestic hot water
Underfloor heating in all rooms
Decentralized ventilation Lunos e² with approximately 90% heat recovery

At a later time, in a few decades, it will still be possible to add external insulation to the facade to reduce the U-value from around 0.2 to 0.08 W/m²K. Furthermore, the roof is prepared for photovoltaic installation, and with high-quality modules, a net-zero energy house could be achieved.
The question always is whether it makes financial sense… especially if the money has to be borrowed on credit and interest must be paid, it takes a long time for such investments to pay off. Currently, this would cost an estimated 40,000 euros and therefore hardly pays off, considering heating costs of about 500 euros per year 🙂

Hello,

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

What was the approximate actual energy demand for heating and hot water calculated and contractually agreed upon?

Nutshell schrieb:
....The question is always whether it is cost-effective... especially when the money has to be borrowed with interest, it takes a long time for such investments to pay off. Such a system currently costs an estimated 40,000 Euro and is therefore hardly worthwhile, with around 500 Euro heating costs per year 🙂

Correct, but how the figure of 500 €/a was derived is probably only known by the inventor of that number ;-)

Best regards

Increasing insulation from 14 to 16cm (5.5 to 6.3 inches), air-to-air heating system (manufacturer currently unknown), and upgrading windows to triple glazing (previously Veka with double glazing and a Ug value of 1.0) is estimated to cost €12,500. Is this justified? I find it a bit quite high, especially considering that the gas connection costs have already been offset.

Why is that too high? That seems like a realistic price...however, I would skip the air-to-air system and stick with gas...but if someone can’t build a KfW-70 standard house with gas, they should look for customers elsewhere...

Hello,

Nutshell schrieb:

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

That’s true, and moreover, it makes no sense in the combination presented.

Nutshell schrieb:

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

If you mean a "standard" gas boiler/solar setup, that is a bold statement; the location of the house relative to the sun is crucial. In theory this is possible, but in practice it is quite rare. Additional measures often need to be taken.

Best regards, Bauexperte