Four channel remote temperature sensing

I'd like to put a temperature sensor on each floor of my house, and have them wirelessly report the data to a central location for graphing/reporting.

Can I use my existing wifi network, or do they need to communicate via bluetooth?

Do I need a PC to collect the data, or can they send the data to a website?

What's the best way to approach this project?

If you mains power e.g USB power supply / charger etc the thermometers you can use what you like.
You could put wifi in all of them, and get them to directly post data to your web site.

If they have to be battery operated, its a different matter. I suspect that you’d need to use something like a JeeNode for each thermometer and then have a “base station:” Arduino with wifi or ethernet that is connected to power.

You don’t need a PC to be part of this system for it to operate.