NPT vs Compression fittings

[Super47]

Hi there,

I'm in a job right now specking out a tankless water heater. The old one we had uses 1/2" NPT male fittings. The new one uses 3/8 compression fittings. Can someone very simply explain to me what the difference is between NPT and compression fittings? I don't understand the scope.

 

[Twowaxhack]

Npt uses opposing pipe thread to seal

Compression uses a ferrule/ferrules that bite into the tube and compresses against the fitting wall.