This increases the efficiency (energy delivered into the building vs. heating value of gas purchased) to over 90%.
ðɪs ɪŋkɹˈiːsᵻz ðɪ ɪfˈɪʃənsi ˈɛnɚdʒi dᵻlˈɪvɚd ˌɪntʊ ðə bˈɪldɪŋ vˌiːˈɛs. hˈiːɾɪŋ vˈæljuː ʌv ɡˈæs pˈɜːtʃɪst tʊ ˌoʊvɚ nˈaɪnti pɚsˈɛnt.