Abstract: A heating system for a mechanical compressive shrinkage apparatus in which a continuously flowing liquid heat exchange medium is caused to flow in series through each of the components required to be heated. Heat is input to the flowing medium in accordance with the temperature of one of the components to be heated, preferably the first in the series. Uniformity and constancy of both absolute and relative temperatures of the series-connected components is achieved. A mixture of water and propylene glycol alcohol is an advantageous heat exchange medium for the purpose, which allows operation at lower pressure without the maintenance problems of a system using, for example, oil as the exchange medium.