Newbie Question: US 100V Soldering Iron and Step-Down Transformer

Hi there

I am looking to buy a a desoldering iron from the US that is 110V with

I am looking to buy an appropriate step down transformer for it.

Is a 50W step-down appropriate or do I need to get something more powerful, say 100W or higher?

Is there a difference between certain step-downs, ie some are for appliances with heating elements and some aren't?

Thanks for your help

Ric