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http://www.ydravlikos.gr/portal/index.php?option=com_content&view=article&id=321:----------&catid=57:-&Itemid=107
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The condensate expelled from a condensing boiler is acidic, with a pH about the same as an orange (between 3 and 4). Condensing boilers require a drainpipe for the condensate produced during operation. This consists of a short length of inexpensive polymer pipe with a vapour trap to prevent exhaust gases from being expelled into the building. Though the mildly acidic nature of the condensate poses no health risk to occupants, it may be corrosive to older cast iron plumbing waste pipes and concrete floors. A neutralizer is employed in such cases, typically consisting of a plastic container filled with marble or limestone aggregate or "chips" (alkaline) to raise the pH to acceptable levels. If a gravity drain is not available, then a small condensate pump must be installed to lift it to a proper drain.