Currently have 6. I need to get more, and larger ones. We live in a log house, in an area that takes a minimum of 20 minutes for emergency services to get to, and heat with a wood stove. We absolutely need to practice fire safety all the time.
That's the idea. The really big ones get pretty expensive though; a 30# fire extinguisher starts at around $500, and can get up to about $1500. But that size gets you about 20-30 seconds of continuous use, which is enough for a pretty big house fire.