iPad Air 1st edition gets very hot when charging

Any 12 Watt or greater charger should work.

The iPad Air First Generation was released in 2013 and as such if still has the original battery it may be too old to reliably re-charge can cause a lot of heat build up. You may want to take it in to an Apple Store or Apple Authorized service provider and see if they can replace the battery for a new one.

click here ➜ Apple Service and Repair for iPad - Apple Support

If you are referring to a different iPad model, then please clearly identify it.

click here ➜ Identify your iPad model - Apple Support

It is perfectly normal for the Power Adapter to become very warm while charging a connected device. That said, it should not become uncomfortably hot to touch.

The first generation iPad Air was supplied with an Apple 12W Power Adapter with a USB Type-A connection - along with a USB Type-A to Lightning charging cable. Apple now only supplies Power Adapters with a USB-C connection.

Any Apple USB-C Power Adapter will be suitable to charge your iPad Air1 - although anything greater than 20W will offer no benefit. If using a USB-C Power Adapter, you will require a Lightning to USB-C charging cable:

• USB-C to Lightning Cable (1m)

USB-C to Lightning Cable (1m) - Apple