You use a. You only use an in front of words that start with the vowels a,e,i,o,u.
ANS2:It depends on your dialect. before words with an aspirated "H" you use "a" such as "A hot water faucet". If the "H" is silent the vowel needs to be separated by using "an" as in "Anhour". In some dialects silent "H" is more common.Chat with our AI personalities