Th reason why it is 'an hour' but 'a house' is that the 'h' is preceded by 'an' and treated like the vowels 'a, e, i, o,u ' in case it is not pronounced such as in the word 'hour' .It sounds like 'our' then. In case the 'h' is pronounced as in 'house', the word is preceded by 'a' ,because it starts phonetically as well with a consonant. So the choice between the indefinite articles 'a' and 'an' in the case of preceding a word starting with the consonant 'h' depends on the pronunciation of 'h'.

H is confusing in English: we have a Germanic tradition which says it must be pronounced, and a Latin(French) tradition which says it must be silent. Ignore any written rules about this. You use "an" when the next *sound* is a vowel. It's smoother to pronounce that way. So: a horse, a house, a hair - the H is pronounced here. But: an hour, an honour, an heir - the H is silent. Same with words beginning with U. If it's a basic vowel "uh" such as umbrella, unusual, up-side, then "an" applies. If there's a "yuu" sound as in university, utopia, Uruguayan, use "a".

Holajjj

se escribe a house es igual una casa

Si,estoy de acuerdo con Martin ,it's "a house .Me gustaría añadir lo siguiente:when u say "una hora",it's "an hour "in English .