Hard water isn’t just a plumbing nuisance—it’s a heat-transfer killer in light commercial and residential HVAC. A thin film of limescale on heat exchangers (tankless water heaters, combi/condensing boilers, hydronic coils) acts like insulation, forcing equipment to burn more energy to deliver the same BTUs. Multiple industry sources attribute about a 7% efficiency hit from just 1 mm of scale, which compounds into higher utility costs, longer run times, and premature wear.