ᐅ Is a 30 cm ThermoPlan S9 brick wall sufficient?

The 36 cm (14 inch) brick will likely have a U-value closer to 0.24 W/m²K instead of 0.28 W/m²K.

This means around 0.04 × 70 kWh more heating per year per m² of wall. For 100 m² of wall, that’s about 300–400 kWh of heat energy per year, roughly 100 kWh of electricity equivalent. You can compare that to the €8,000 and calculate whether your grandchildren will live long enough to recoup that investment.

Alternatively, you could install an 8,000 € / 5 kWp photovoltaic system on your roof and generate about 5,000 kWh of electricity annually.

The heating system won’t be more expensive because of this. It is usually oversized anyway, and the supply temperature and annual performance factor can be influenced much more by the design and heating circuit planning. Use plenty of insulation where it is cheap, especially in the roof and try to avoid thermal bridges (which actually requires some clever planning).

This isn’t exactly rocket science, and even though the numbers are just rough estimates, it’s a clear “no-brainer.”

That’s a very clear rule-of-thumb calculation – thanks!

Just to clarify:

• What do the 70 kWh refer to?
• The conversion from the 300–400 kWh of heat to electricity is based on the annual performance factor, right?

Thanks also for your other tips!

matze007 schrieb:

That’s a very clear rule-of-thumb calculation – thanks!

Just to clarify for my understanding:

• What do the 70 kWh refer to?
• Is the conversion from 300–400 kWh of heat to electricity based on the annual performance factor?

Thanks also for your other tips!

The 70 kWh per m² (square meter) is a guideline for the annual heating energy saved when the U-value of a building component is improved by 1 W/m²K.
Yes, the conversion is based on the annual performance factor.

dertill schrieb:

and the supply temperature and the annual performance factor can be influenced much more by the design and heating circuit planning

Exactly. The combination of well-designed heating surfaces and a properly planned and operated heat pump achieves much more than slightly better insulation. Even the ventilation system contributes more to reducing heat demand and improving the annual performance factor than the best wall insulation could.

Your time is better invested in heating system planning.

Add photovoltaic panels as long as it remains cost-effective, and you will have a significantly lower energy consumption than many better-insulated new builds.

Only the 36cm (14 inch) bricks could be interesting for sound insulation. More mass is always better in this regard.
You can look at and compare the sound insulation values for this.
A difference of 5-10 dB is roughly perceived as twice as loud.
Windows should not be overlooked when considering this, as the best wall is useless if the windows are noisy...

face26 schrieb:

In general, I wouldn’t necessarily recommend heating with a heat pump in a house built right at the energy-saving regulation limit.

It’s a matter of perspective. Three to four years ago, this corresponded to KfW 70 standard. Back then, people talked about it the same way they do today about the current KfW 55 standard — just fancy stuff that supposedly doesn’t pay off. Of course, it really depends, but also on future energy prices. The cheapest kilowatt-hour is the one you don’t need at all. Grandma in a 1960s house probably wouldn’t have expected to spend 250€ per month on heating oil back then. But these are timeframes you simply can’t predict.

Monolithic construction tends to be more expensive when upgrading. If you are already installing external thermal insulation composite systems (ETICS, also known as external wall insulation or EIFS), adding 2–4cm (about 1–1.5 inches) of insulation usually covers the essential improvements.