In summer 1990 we moved into our house in Würselen near to Aachen. Our daughter has just come into our world and so we were three then.

Our house is a semi-detached house with an additional wall of clinker. It had got 124 m² of living space then. The insulation was carried out according to energy saving regulations of 1990. The energy requirements were calculated to 12,5 kW. The cellar has not been heated except for a small radiator in the open staircaise. The attic was  not yet prepared for living, but we added the insulation after the first cold nights in October 1990.

Instead of the planned radiators in first and second floor we decided to install an underfloor heating (and that was a very good idea)

Three years later we got another child. And in 1995 it was time to plan and fit out the attic when our third child announced it's arrival. So we added  26 m² of living space in the attic. It was prepared wth two radiators, which are included into the under floor heating cycles. Therefore the radiators had to be planned a little larger. Though one can hardly feel that they are warm, it is more than sufficient for our attic. The energy requirements were calculated to 2 kW. When I fit out the attic I provided well insulated flow pipes and return pipes and a wire as a precaution for the case that a thermal collector should have been installed on the roof one day. The pipes and the wire lead into the cellar using a drain crossing two ceilings.

The heating for the house was a WOLF boiler and warm water was prepared by a VAILLANT boiler of 180 l.

My solar fitter was laughing when he saw those devices from 1990 and raised his energy saving prognosis (but he was still to low). But some people in Germany will say: "Hey, I've got another device like this in my cellar!" Everyone, who says this, should read carefully here then he should plan and act.

Thanks to low gas prices we lived happily for 15 years in our house until the day I checked the gas invoice for 2005 in spring 2006. On a monthly base I have noted the usage of gas, water and electric power since 1990. With this data I produces nice diagrams. But on that rainy Sunday I got the idea to take the gas invoices of the last 15 years  and to produce new diagrams including the costs (base costs, coal cent, usage costs, taxes and so on).

The costs for gas usage had been stable on a low level for a long period, but since 2000 a strong increase can be noticed. From 2000 to 2005 the increase had been 8% each year or 45% within 6 years. Assumed that the price for gas will increase 5% each year, then one m3 will cost 1,43 Euro in 2030. But the price for gas increased by 16% in 2006, so my assumption was wrong. The projected result would be more than 15 Euro in 2030 and could not be payed any longer.

In some reports I found that peak oil will be reached around 2009. From then on oil production will go down continously. In my opinion, if you think of countries like China and India, which have a big yearning for energy right now, because they are Newly Industrializing Countries with billions of people, the price for gas must increase inevitably in view of a decreasing supply and an increasing demand.

Startled by this I remembered that I still had the option for the thermal collector which should be put into action now. 

The objective was to reduce the usage of gas by at least 50%!

From 1990 to 2006 we used 2735 m³ of gas in one year on average. Calculated to one m² of living space it is 18,2. This was poor. Now we want to use around 1350 m³ of gas each year or 9 m³ of gas for one m² of living space a year. This not yet the value for a low energy house, which starts at 7 and less, but it would be very good.

After some investigations in the Internet I realized that a thermal collector on it's own couldn't do that job for our house. Therefore I had to check the heating and the warm water preparation.

Since ever I hated the pilot flame which both devices used, but people said,  that there was no need to mention it, because of the few gas they used. I could not believe. Therefore I stopped the time in front of gas counter and I was surpised:

35 m³ of gas used for almost nothing! My plumber would not believe and I repeated the measuring: Same result!

I got angry with this and so the decision to kick off both devices was not hard to find.

The solution:

• Kick off old heatings
• Installation of new heating "Brennwertkessel" combined ...
• with a thermal collector installation for heating support and warm water preparation

The questions: