Exhale - Homegrown Co2 for Your Indoor Plants - "Professional 2 Pack" Save with "Professional Grower - 2 Pack" ExHale-Homegrown CO2 is a revolution in indoor CO2 production systems. Maintenance Free! No Heat! No Electricity! Just CO2!! Place the ExHale cultivator slightly above the height of the plants in your grow space. CO2 being heavier than O2 will precipitate downward towards your plants ExHale- Homegrown CO2 is a more harmonious way of providing your plants with CO2