Pisac is considerably warmer than Cusco, and due to the thick adobe walls and small rooms, heat is retained and very few guests comment on the cold. We have warm alpaca blankets and down comforters, and extra blankets or hot water bottles are available upon request. We also have electric heaters when needed. It is good to bring warm lightweight layers, as the common areas of the hotel are not heated, and can be very cold especially in the months of June, July and August.
External Link to weather in Cusco: http://www.world-guides.com/latin-america/peru/cusco/cusco_weather.html