120V heater pad
- Use resistors instead - 
Halogen As Heater
- Halogens are about 85% heaters.
- For 3D printers, use a 240V bulb, run it at 1/4 power with 120V (P~I^2R) so it doesn't burn out with on-off cycling - by running it only at a fraction of its rated power.
- Use a holder - 4.69 or 4-11/16" holder, for a 240V T3 bulb. 
- R7S is the style of holder -
- This bulb is T3 R7S, 118 mm long - 
- 1500/375W 240/120v - 
- Or use 2 120V 500W in series, more even bed heating, using 2 bulb holders -