Framing nailers exist to help erect wooden frames, hence their name. You can use a framing nailer to nail any two pieces of lumber together. These tools provide general assistance in erecting wood-framed buildings. Siding nailers exist specifically to install siding on buildings. These nailers may exist for use with sheathing, or wooden siding material, placed over wood building frames, though they also may be designed for use with various other siding materials. Some manufacturers advertise siding nailers designed for use with sheathing as sheathing nailers, not siding nailers.
The materials with which you can use a framing nailer or siding nailer help differentiate the two. Framing nailers are designed for lumber only. Siding nailers, on the other hand, allow you to work with lumber or siding materials like aluminum and vinyl. A siding nailer designed for use only with lumber, or wood sheathing, only differs from a framing nailer in name – they contain the same basic technology and capabilities. Siding nailers designed for use with aluminum or vinyl siding, however, exhibit different power outputs than framing nailers.
Framing nailers and siding nailers use different types of nails. A framing nailer uses nails designed for lumber, usually ranging in length from 1 1/4 to 2 1/2 inches long. Siding nailers use different types of nails depending upon their purpose. Aluminum siding nailers use aluminum nails, which work best when nailing aluminum siding to a frame. Nailers for vinyl siding use different nails still. Some siding nailers may offer the ability to handle nails for aluminum, vinyl or wood siding, which you load in clips, like a gun.
Ultimately, the differences between framing and siding nailers come down the nailers in question. Each manufacturer maintains its own definition of a siding nailer, some of which differ in no way from framing nailers, others of which are completely different. When buying or renting a nailer, the easiest way to tell the difference between a siding nailer and a framing nailer entails looking through the manual or specifications for each and comparing them directly to one another. You can also consult hardware store employees or builders.