The heat (enthalpy) of dilution for some acids is given in this link. 31.45% HCl is around 10 so the heat of dilution is roughly 10 kJ/mol. 38.5% Sulfuric acid, by comparison, has a heat of dilution of around 28 kJ/mol so substantially higher. This link calculates the temperature rise for a specific example of adding acid to water and explains why adding water to acid is not a good idea. It basically has the water heat up so much that it can boil and splatter, causing acid to be propelled with it risking getting splashed with concentrated acid.