Space heating energy demand is quite substantial irrespective of sector in British properties. Recent advances on Renewable Heat Incentive (RHI) and other solar thermal related policies and government interventions are making the area of low-energy thermal more exciting and promising to stakeholders and building owners. Objective for the development of building integrated low-energy solar ventilation unit (LESVU) is to provide pre-heated ventilation air for new build or retrofit. The developed system consists of transpired solar collector (TSCs) also known as perforated absorber of unit area 1.00 m² to check their expected performance. Transpired solar collectors are an unglazed once-through solar air system with a perforated absorber. TSCs use solar energy to heat the absorber surface and heated air is being sucked by fan unit. The absorber surface is generally made of steel. By drawing air through the multiple small perforations into the cavity between the skin and façade the contact surface between the metal skin and air is increased. Finally heated air is distributed into the building to provide space heating, ventilation air heating or pre-heating by operating the unit in different efficiency regimes. During summer season the warm air in the cavity can be released using a by-pass damper to avoid over heating inside the building. The LESVU unit can deliver very high efficiency of solar thermal conversion up to 50 % when operated using high flow rates of 120-144 m³/m²/hr. However low flow rates in the range of 30-60 m³/m²/hr provided more temperature lift but lower efficiency.