Originally Posted by
fumitani
Check to see on the NH homepage if there is C award. If so they use the same inventory for upgrades
If using partner miles it would be better to search using United, Aeroplan or another partner interface. That will show what the partners have access to.
If you're looking for Y->C then you need I inventory, just like a regular biz award. And you need to be on a Y or B fare to use miles for the upgrade.
You can use the regular United.com award search page to see if the inventory is available. If you want to set something up to monitor for award space and alert you should it open one of many options is
the tool I built for Star Alliance award alerts.