Hello, I plan to change my gas boiler and I hesitate between a condensing boiler or a traditional boiler, because I have large cast iron radiators. I had contradictory information about this: I heard and read that the condensing boiler is not suitable for this type of cast iron radiators because the water is too hot to the boiler that does not condense, and the I was told that on the contrary this boiler is quite suitable for cast iron emitters because of the large amount of water circulating. I put the question to 4 different boiler manufacturers at the Paris Fair, and all, without reservation, confirmed me the 2nd statement (condensation). I do not know who to believe anymore. Do you have the answer?
All the reasonings described have their share of truth.
To condense, a boiler must actually operate with relatively low water circuit temperatures around 40° C. These temperatures are well suited to recent constructions, very insulated and equipped with underfloor heating called "low temperature", as well as radiators operating with a low water temperature.
In old buildings equipped with conventional radiators, water temperatures are often higher, 50° C and more, and in these cases, the boiler condenses little, if any, at all.
Nevertheless, these old installations were generally oversized, and the insulation was most often improved over the years. So we sometimes see old facilities provide a sufficient level of comfort with low water temperatures, and that allow the boiler to really condense.
Then you have to calculate the overall economy. A condensing boiler is more expensive to purchase, and it requires the installation of a condensate resistant conduit, provide about 150 euros per linear meter. If the pipe has a height of 10 meters, it represents an extra cost of 1500 euros. There is a much cheaper alternative, which is to abandon the original conduit to install a suction cup, but all configurations do not allow it.
In any case, the application of the European Ecodesign Directive 2009/125 / EC sounds the death knell of low temperature boilers and generalizes the installation of low temperature boilers from September 2015.
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