On the basis of a short description of electric compression heat pump, an overview is given of the different sources and exchangers used in our projects, in Belgium, during the last two decades, namely: - at cold source: - Water loop in ground, water or even air. - direct expansion in the same, solar assisted for air source. - at the hot source: - water loop in radiant floor heating, - direct condensation in the same and in naturally ventilated convectors. The necessity and advantages of a could source storage is stressed.