Buildings consume 40% of the total global energy and contribute to over 30% of all CO2 emissions. Space heating forms a significant part of energy consumption in buildings. A possible solution is to recover waste heat from sewage and to upgrade its exergy using a heat pump. Polymers reduce cost and energy required for manufacturing the heat exchangers. The impact of sewage flow and temperature, heat exchanger dimensions and thermal enhancement of polymers on heat recovery is studied using a Matlab model. The model integrates a sewage heat exchanger with a heat pump and optimizes heat recovery from sewage. A heat pump is used to obtain hot water at 55°C for space heating. Heat recovered from sewage and overall COP are quantified. In case of HPDE with graphite filler, increase in filler content from 0% to 30% increases thermal conductivity from 0.46 to 1.89 Wm-1K-1 increasing the heat recovery with 34%. The heat transfer coefficient becomes twice as large when polymer with no filler is enhanced with 30% filler content. Large heat exchange area and variability of sewage level limit the recovered heat.