Greetings Gang!

I have acquired some electric baseboard heaters from my sister. I have taken them apart trying to find some writing as to wattage so I can figure what type of wire I need, however, there is no writing anywhere to indicate name, model, wattage or anything.

Is there any other way to determine wattage?

If these came from a home, most likely they are 240 volts. Most units can handle 208 volts up to 277 volts.
The typical wattages are typical to the general footages:

2 ft -350-400 watts
2'-6" -500 watts
3 ft -750 watts
4 ft- 1000 watts
5 ft 1250 watts
6 ft - 1500 watts
8 ft new can be 2000 or 2500 watts to replace older 10 ft 2500 watt units
10 foot 2500 watts.

A few popular brands are:
Baseboard Heaters
http://www.dimplex.com/images/pdfs/e...seboard_bn.pdf
Berko Products
Built-in Electric Heaters

Perhaps you can identify the brand by the appearance.

It is important to either know what voltage they were connected to so as to be sure what voltage shlould be supplied. If lower voltage is connected, say 208 when they are rated for 240, the heat output is reduced proportionally, and vice versa for higher voltage .