A Condensing Boiler for Hot Water

After a lot of research into different methods for obtaining domestic hot water, suitable for our home, we decided on a condensing gas boiler. In Barcelona, where we don’t have access to an alternative energy source (yet?), we concluded gas would be the most efficient way to heat the water for our shower, kitchen and central heating. The condensing boilers are especially environmentally friendly because of their efficient use of the gas and their considerably lower CO2 (responsible for global warming) and Nox (responsible for acid rain) emissions. We needed a combi-boiler in order for it to provide hot water for central heating as well as domestic hot water all year round.

In the wall-mounted boiler Cerasmart by the German brand Junkers, widely available in Spain, we found what we were looking for. The advantages: gas saving and low emissions.

How does it work?

The condensing boilers recycle the energy that is normally lost through the duct into the atmosphere. It catches the water vapour produced by the burning of gas for it to condense back into water. This way the heat, produced as water vapour, is recovered and the boiler uses less gas. Image by Junkers

“Typical condensing boiler efficiencies are around 90%, which brings most brands of condensing gas boiler in to the highest categories for energy efficiency. Condensing boiler manufacturers claim that up to 98% thermal efficiency of fuel conversion can be achieved in normal domestic use, compared to 70%-80% with a conventional design." (Via Wikipedia) Junkers claim the boiler Cerasmart to be 21% more efficient than standard ones, due to the fact that it can work at lower temperatures.

Condensing boilers are especially recommended if you have under-floor heating, low H2O radiators (like us) or other energy saving heating solutions.

A slight drawback is that you need to install an extra draining pipe to get rid of the condensate. This can either be installed vertically through the roof, or diagonally through the wall to the outside. (see photo on the right)

Another disadvantage might be the fact that condensing boilers are generally more expensive than conventional ones. It is estimated that “as of 2006, at UK prices the extra cost of installing a condensing boiler should be recovered in around 2-3 years” (via Wikipedia).

The Cerasmart boiler, for a 4-people flat with central heating by Junkers will cost you around 2268€ in Barcelona (you might be able to get a standard one for under 1800€). We bought ours at Tuysa.

Why we didn’t go solar.

Solar Hot Water Panels would have been the most eco-efficient solution, but all the companies we contacted turned us off the idea. Technically, so they say after visiting our flat and roof, it would be very difficult due to the distance (2 floors) the water would have to travel to and from the roof. Plus we would have to give up 2 of our precious 58 m2 to make space for a not so beautiful water tank.

The initial first cost didn’t help make our decision easier as it would have been at the very least 2000€ for the panels to which we would have to add the installation cost and a back-up boiler. Moreover, we would have to get the approval of the fellow property owners of our building to install the solar panels on the communal roof. This shows again that eco-renovating a flat within the city is a very different story to building an eco house in the countryside where space and neighbours are less of an issue.