Vestaxx window heating - experiences?

But if you have already been able to gain new insights in the meantime, I would be happy if you share them with us.

One insight I have been able to find out so far is that the window heating should cover 20% of the area to be heated. In other words, 20% of the floor area of the room.

Hello EinHausfür5

I heat my house exclusively with the water-based wood stove (17kw). My house dates back to 1951 and was completely renovated about 10 years ago and insulated to passive house standards. Unfortunately, the wood stove is not quite sufficient for domestic hot water and heating water. That means: The house is properly heated to 20°C in winter at an outside temperature of -5°C. Unfortunately, I have two cold-sensitive people who are not satisfied with this standard.
Now I am in the process of converting the attic for one child, or rather finishing it, because the walls (sloped) are of course already finished. What is missing here is the heating. That is the real problem. For a water-based system, the vertical walls are missing. For underfloor electric heating, the required air gap after doubling the floor would be missing (too much space would be lost if another 2cm layer were added on top of the floor).
Now, during the construction phase, I placed a panel infrared heater with 0.8m² in the room, and behold, the temperature rose significantly to 19°C. That is sufficient for working.
I have also heard of the Vestaxx system and the statement sounds plausible that with twice the heating surface you can get the room to a temperature well above 19°C. The question of economic efficiency remains. This brings me to the general demand to equip every house roof with photovoltaics. I have such a system on my roof. With about 8.5 kw, heating with electricity is not so difficult for me. If one does not have a photovoltaic system, one has to discuss with the energy supplier how a cheaper tariff generally looks if heating is done with electricity. In the past, many households had night storage heaters. The bad reputation of these "heaters" came only from poor economic efficiency. Night storage heaters, however, are not comparable at all with steamed glass surfaces, as the way heat is generated is completely different. Most heat is still lost today through window surfaces and not through outer walls. A big advantage of heated window glass is that the temperature in the area of the windows does not drop but is equal to that of the inner walls. Thus, there is no effect of the usual thermals in the window area that are perceived as uncomfortable. So anyone considering creating a more comfortable environment is well served with this system. And there are also common systems for domestic hot water heating. One does not have to install a heating system costing several tens of thousands of euros for that.

I will have my roof windows replaced with the 'converted' glass. After that, I will report on the effect.

I wish you a good, healthy, and comfortable new year

water-guided wood stove (17kw). My house is from 1951 and was completely renovated and insulated to passive house standard almost 10 years ago. Unfortunately, the wood stove is not quite sufficient for domestic hot water and heating. That means: The house is properly heated to 20°C in winter at -5°C outside temperature.

Find the mistake(s)!
Where are the 17 kW going to waste that the place doesn’t get warm?
Passive house standard? :rolleyes:
No hot water?

I assume typical one-day flies. With "questionable" products, like this window heater as well as in the parallel thread to HPL Picea.

Then the fairy tale of being able to significantly support an electric direct heater with photovoltaics in winter. In any case, I had less than 100kWh yield in December.

I had less than 100kWh yield in December anyway.

And then only at most between 9 a.m. and 4 p.m. In the rest of the time (e.g., cold night) you have to buy expensive electricity.

Hello everyone,

this is the manufacturer Vestaxx GmbH writing in the person of the CEO.

Unfortunately, I only became aware of the questions, concerns, and comments in this very interesting forum today. As the system provider of the window heating, I would like to share a few clarifying points. First of all: Of course, we are interested in the distribution of our systems and thus also in positive news here in the forum, but we gladly welcome any constructive criticism and are happy to answer all questions about our heating system. If we do not convince you, we advise: Please do not buy our system!

I cannot answer all the questions raised here now – that would go beyond the scope – so I refer to a webinar created a few months ago for energy consultants of the GIH, which can be found on our homepage.

Basically, I would like to consider the following: According to current statistics, a heat pump is installed in about every second new building. The current cost for an air-water heat pump is about €40,000. For the same money, a building family receives a window heating system (only surcharge for the heating function) including installation. In a single-family house, the price is about +/- €10,000. So the building family saves about €30,000. For this, they can buy a domestic hot water heat pump as well as a very large photovoltaic system including a battery storage.

Example calculation of heating energy demand and hot water generation as well as household electricity (total energy demand of the house): Basis: 150 m² living space / 4-person household / KfW40 building standard specific heating energy demand = approx. 30 kWh/m²a, i.e., 4,500 kWh + approx. 12.5 kWh/m² hot water demand 1,875 kWh (let’s say 2,000 kWh). Additionally – and unfortunately this is always forgotten – household electricity comes on top -> 4,000 kWh/year. Together approximately 10,500 kWh annual energy demand.

What costs do we have now for covering the energy demand?

Heat pump system -> heating energy demand 4,500 kWh / annual performance factor (3) -> 1,500 kWh per year (I know many will now again demand an annual performance factor of 4. To those, I would advise not to rely on the numbers from brochures but on independent studies from recognized institutes. There, an average annual performance factor of 2.6 is given for the air-water heat pump). In addition, there is a utilization rate of 70% (source: TU Berlin – Hermann-Rietschel-Institut) and we end up below 2! However, since I am not dependent on these 2 here, let us take 3. (Note: Actually, I could also assume 1,000 here, but more on that later ;o)) So: hot water demand -> from 2,000 kWh it becomes approx. 750 kWh (annual performance factor = 3) and then the household electricity -> 4,000 kWh. Together the household with air-water heat pump system therefore must buy 6,250 kWh of electricity. Assuming a current electricity price of €0.35/kWh, that is about €2,200 per year.

And now let us see what comes out with an electric direct heating system (heating glasses + domestic hot water heat pump + 15 kWp photovoltaic system including battery storage). Heating energy demand = 4,500 kWh Hot water demand = 750 kWh (DHW heat pump with annual performance factor = 3) Household electricity = 4,000 kWh Together 9,250 kWh.

Aha – some of you might say now. 3,000 kWh more than with heat pump! I told you!!!

True, but what about the photovoltaic system?

A 15 kWp photovoltaic system affordable with the money saved produces even with not so good orientation and not so good location still approx. 900 kWh/kWp. That means the system produces approx. 13,500 kWh (CO2-free) electricity annually -> about 2/3 in the summer half-year and about 1/3 in the winter half-year.

Let’s look at the annual balance: The house produces more energy than it consumes in a year -> called a plus-energy house!

In the above constellation, at least half (more likely more) of the generated electricity is consumed directly in the house – so approx. 6,500 kWh. That does not need to be purchased. The remaining 6,500 kWh is fed into the grid and remunerated at approx. €0.08/kWh. That is about €500 annually.

And now let's look again at the energy costs of the electric direct heating system: 9,250 kWh minus 6,500 kWh leaves only 2,750 kWh, and yes, this is to a large extent purchased winter heating electricity. 2,750 kWh at again €0.35/kWh = approx. €1,000, i.e., about €1,200 annually less than with the heat pump system!

And that is not all, because those who paid attention will have noticed that we have not yet deducted the photovoltaic remuneration of €500. That would leave only €500 total energy costs for the electric direct house.

THAT is why we do it! Our previous customers thank us for it. Of course, you can also recalculate the above calculation with an annual performance factor of please 5. It does not help much!

At this point, I will stop because it has gotten a bit out of hand. But anyone who wants to build a single-family house should take the time to think about it. Please feel free to recalculate for your case and openly ask questions or give criticism here. I will respond promptly.

Best regards – Andreas