Patients over the age of 18 referred to, or under follow up at, the Royal Brompton Hospital who require domiciliary NIV but are inexperienced with use of NIV will be considered for entry into this randomised crossover study. If eligible for inclusion and willing to take part patients will be setup on automatically adjusting NIV or standard NIV, assigned in random order. At the end of one month the patient will be swapped to the alternative NIV for a further one month of domiciliary NIV treatment. At the end of each one month treatment period the patient will undergo overnight polysomnography, transcutaneous CO2 monitoring and 24 hour Holter monitoring.