Yosemite Startup Manager After Downgrading to Mavericks
The question does not mention a model, let's assume that the Mac is a model that gained a firmware update in connection with Yosemite. 

If so, then – for use with Mavericks (without Yosemite) – it may be desirable to reinstall lesser firmware.


  … Erased HD …


– that would have erased an operating system without affecting firmware. 

A suggestion


System Information will tell what firmware is installed
compare what's installed with https://web.archive.org/web/20141010090340/http://support.apple.com/kb/HT1237 (the 2014-09-23, pre-Yosemite edition of an article)
compare what's installed with the current, post-Yosemite edition of the same article: EFI and SMC firmware updates for Intel-based Macs – Apple Support.


Related

Amongst Macs that can be upgraded to support OS X Recovery, can any model not accept a firmware downgrade?

Kernel Programming Guide: The Early Boot Process