When installing a Digital Terrestrial Television (DTT) receiver in a household, it is important to have a measure of how far the reception conditions are from those leading to errors being noticed on the decoded picture or system failure point. Usually the installer has no means of either evaluating the quality of the transmission channel or estimating the carrier to noise ratio at the input to the receiver. Therefore the noise margin of the DTT installation is unknown. Channel State Information (CSI) is crucial for any DTT receiver to work properly under poor reception conditions. This paper shows how an estimate of the average CSI can be effectively used to characterise the performance of a DVB-T system subject to different types of impairment. A thorough comparison between CSI and other performance indicators gives support to the use of CSI to estimate the noise margin in a DTT installation.