... 25mm heat pipe collector: Keymark(EN12975)solar thermal heating collectors system 15-30tubeEuropean standards,Could be used for underfloor heating systemsize ... Thickness: 55mm Heat pipe dimension: Ø58 x 1,800mm Number of tubes: 20 pieces Collector area: 2.88m² Tube ... more details about our Keymark(EN12975)solar thermal heating collectors system, please check our website, or email us. Keymark(EN12975 ...