Apart from heating the building, heating DHW is the second largest expense in a family budget. After more than 25 years on the market, today it goes without saying that a heat pump is the most economical way of heating DHW. The costs comparison of heating DHW for an average Slovenian family with various energy sources proves the above statement. The cheapest way of heating DHW is closely followed by solar collectors (SSE) if they are placed in an ideal position. This is only true until we compare the investment. The investment into SSE is usually 2 x higher than an investment into a DHW heat pump.