A 450W motor is about 1/4HP. It's a 2-speed motor, which you may or may not care about when replacing it. I'd say you should take the motor out and take it to Grainger or another industrial supply house, and see if they can get you a replacement. Alternatively, measure all the important dimensions and look for one online. Burden Sales (www.surpluscenter.com) usually has a suitable cheap replacement for most small motors. The replacement doesn't have to be exact, or even really close. They key things to look for in a replacement are: Enough power (at least 1/4HP, more is fine), correct direction of rotation, mountable (even if you have to drill new holes), and the ability to line up the motor pulley with the fan's pulley. You may need a new pulley if the motor has a different shaft or a different speed.