Should a homeowner expect more caco3 buildup in hot water pipes or cold water pipes

             CaCO₃ built up in hot water pipes

Explanation:

The hardness of water is classified as;

Permanent Hard Water:
                                     In this the mineral content cannot be removed by boiling. This water contains mainly following,

                                        Calcium Sulfate  CaSO₄

                                        Calcium Chloride   CaCl₂

                                        Magnesium Sulfate   MgSO₄

                                        Magnesium Chloride   MgCl₂

These salts does not precipitate out on heating water.

Temporary Hard Water:
                                     In this water the mineral content can be removed by boiling. This water contains mainly following,

                                        Calcium Bicarbonate  Ca(HCO₃)₂

                                        Calcium Carbonate  CaCO₃

                                        Magnesium Bicarbonate   Mg(HCO₃)₂

                                        Magnesium Carbonate  MgCO₃

These salts does not precipitate out on heating water. i.e.

                Ca(HCO₃)₂    heat>    CaCO₃  +  CO₂  +  H₂O

The CaCO₃ are formed in the form of scales.

Result:
           Hence, we can say that that CaCO₃ built up in hot water pipes.