I am trying to figure out why I am getting belt squeal when I turn on the heater. Sometimes I hear squealing with the heater off, but it almost always starts if I turn the heater on.

The belts seem pretty tight, so I am kinda confused.

Any reason it would get worse with the heater on?

 

If belts are tight,they might be glazed-you could try
belt dressing or replace the alternator belt.The reason
they are squealing with the heater blower on is the
extra current draw is putting more load on the alt,making it pull more power from the belt,should
only cause belt squeal with blower on high,if you have
squealing at low blower speeds,probably is the blower
motor bearings squealing

 

It might not be the belt; it could be the alternator bearings (happened to me recently on a different car). I used a stethescope (aka an old piece of heater hose) to find the noise.

 

Well I tightened the alternator belt and the squeal is gone

Thanks