Vestaxx window heating - experiences?

Don’t talk such nonsense.

What does reality look like?
A family takes out a mortgage loan with 3.5% interest and 2% repayment.
And now another €23,000 is added on.
On the same conditions everyone hopes for.
And because of that, the installment increases by €1265/year.

That is reality for most people.

Basically, I’m talking about that there are different options to heat a house and spend money on it.
And from case to case, each decision can be understood.

Among the approx. 400 property buyers I have assisted in the last 25 years, the main question was mostly:
Can I afford this?

And for them it can be that cost savings of €20k play an important role and they then choose a less efficient consumption solution, but at first glance cheaper.

Among the approximately 400 real estate buyers I have supported in the last 25 years, the main question for a large proportion was: Can I afford this? Not, how can I best save energy.

Crystal ball says that in 20 years there could also be much better cheaper photovoltaics that deliver significantly more electricity under unfavorable conditions. And there could be affordable powerful electricity storage systems that are worthwhile because electricity tariffs vary extremely depending on the available electricity volume....

At the first construction, we were still concerned, but now (after I observed the installation back then) - what should happen to the underfloor heating, which is completely embedded in the screed? I mean the pipes? If a pipe actually breaks in the screed (why should it), usually you have coverage for that in the residential building insurance?
I see the risk primarily with the pump or similar components, but they are located above the floor and are replaceable.

I would be less worried about individual providers - if the window heating system catches on, presumably more providers will have established themselves in 20 years.
The decision in favor of window heating rather carries the risk that a subsequent switch to a system with underfloor heating will not be possible without considerable cost. Therefore, possibly more interesting for renovation than for new construction. In existing buildings, one more often faces the problem of not having underfloor heating. And retrofitting it is expensive.

Is that a contradiction? The burden is always the installment + additional costs + reserves. Accordingly, you haven’t necessarily saved anything if you keep the installment small by choosing the cheapest but inefficient solution and instead have four times the heating costs. And various example calculations have already shown here that even in the rather inexpensive cases, the savings of a window heating are lost again over the next 15-20 years due to the electricity costs. In the end, nothing is saved but just shifted into another pot.

That’s something different. If in 20 years cheap photovoltaics come around, then I’ll install some more on the garden shed and carport. If they are very shade-tolerant, also on the north side. The current photovoltaics on the south side should still provide electricity then. And the storage could still be retrofitted for then little money.
Purely energetically, we are slowly reaching the limits of physics. Less than zero heating demand is simply not possible. Considering that many buildings from 1970 check in at 300 kWh/sqm, today’s 25-45 kWh is already very little. A little less and you’re at the passive house (whatever specific number you set the limit at). Then the residual heat from the stove, TV, residents, etc. is enough to keep the house warm. On this spectrum, it also becomes clear that the “future-proof house” from 1990 with 120 kWh represented the usual state of the art at the time but was far from the theoretical optimum.

I try to make it simple, but calculate slightly differently than RotorMotor:
Basics of rotormotor:

150m² with 40kWh/m²a -> 6000kWh/a heating energy demand / electricity price 35c/kWh / 4 people (I’ll assume that now)
What was forgotten? -> Hot water -> 4 people approx. 2000 kWh (according to the Building Energy Act 12.5 kWh/m² - then rounded up)
House electricity for 4 people -> approx. 4,000 kWh

The users therefore need energy for space heating (6000 kWh), hot water (2000 kWh) and household electricity (4000 kWh).
Together this is therefore 10,000 kWh of energy in the above-mentioned house.

Heat pump system
Costs including everything -> €40,000 and this is the basis for further comparison calculations.
Annual performance factor -> I’ll calculate now with 4. (I could also put in 10 here - would hardly matter)

System with heat pump
Space heating 6,000 kWh / 4 = 1,500 kWh
Hot water 2,000 kWh / 4 = 500 kWh
House electricity 4,000 kWh
Energy demand house per year = 6,000 kWh
Energy costs per year 6,000 kWh x 35 c/kWh = €2,100

System with window heating, WWWP and photovoltaics
Space heating 6,000 kWh with window heating (investment = €10,000)
Hot water with WWWP (annual performance factor = 4) (investment = €5,000) = 2000 kWh / 4 = 500 kWh
House electricity 4,000 kWh
Energy demand house per year = 10,500 kWh
Energy costs per year 10,500 kWh x 35 c/kWh = €3,675

Shit :confused: you are all right! Our system requires €1,575 more per year!

Or? What have I not considered so far? -> There are still €25,000 left from the investment.
For this there is a 15 kWp photovoltaic system, which under poor conditions generates about 13,000 kWh annually.
So already 3,000 kWh more than the house balances out annually -> plus-energy house

What happens to the 13,000 kWh?
The WWWP needs energy all year, completely covered by photovoltaics -> 500 kWh
The heating windows need 6,000 kWh, but maybe only about 1,500 kWh is covered by photovoltaics in winter.
About 50% of the household electricity, i.e. 2,000 kWh, is covered by the photovoltaic system.
So together 4,000 kWh from the photovoltaic system remain in the house at a cost of 0 c/kWh.
So the user still has to buy 6,500 kWh per year.

At this moment, both systems are roughly even. What did I forget?

Oh yes - from the 13,000 kWh - 4,000 kWh = 9,000 kWh remain.
Currently there is a guaranteed €0.086/kWh for 20 years from the state (Renewable Energy Sources Act remuneration).
The market value of this electricity was about 32 c/kWh in July 2022 -> good for direct marketers.

Back to the above example house. 9,000 kWh x 8.6 c/kWh = €774 feed-in tariff annually.
The house with Vestaxx window heating therefore has about €774 less energy costs per year than the house with heat pump.
For that money, the user can buy 774€/0.35€/kWh = approx. 2,200 kWh.

This and nothing else is what I try to present here constantly.