Tricky.
No, not tricky, just complicated: Hart's Rules to the rescue:
a) house style for non-technical work would normally be something like 'spell out numbers up to 100',
but b) it's 'customary not obligatory' to start a sentence with spelt out numbers, which is probably why you feel it should be words,
But c) house numbers are always written in figures, which is why it looks right to you.
Personally, spelling out house humbers looks
so odd to me that I'd go for figures, though I agree that voices usually talk spelt-out not figures.
.
Emma