# Petra

Petra likes to bathe in a bathtub with a water temperature of 38 degrees. She turned on the hot water set at 70 degrees and left for a moment. Before she returned, 40 liters of water flowed into the tub. How much water with a temperature of 22 degrees must allow making water of the required temperature of 38 degrees

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**Dr Math**

For heating engineers - it is highly inefficient to mix water this way. Mix high hot with cold, in addition to scalding. Gas boilers have the highest efficiency when heated to max 40 ° C. the higher the required temperature, the higher the flue gas temperature in the chimney, and the lower the efficiency. Those who have condensing heaters know and there is a second problem that conventional condensing boilers heat the DHW in the storage tank e.g., 66-80 degree water, which does not achieve the ideal 100% condensation. The water needs to be heated relatively slower

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