Do remember if you are using in camera metering that the metering is not calibrated for how you are shooting, an IR film with an IR filter. The camera meter is setup for more normal full spectrum lights and you are cutting most of that out with your filter, right?
As Schafphoto points out the different IR films will respond widely to how much of the light your camera meter sees is IR as you are blocking most of the visible light from the film as you use the IR filter.
If you use tungsten lights most of what you have is IR light, if you light and meter with florescent it will be very different. So what you will most likely need to do is to calibrate your film, filter, and meter to a given situation - such as full sun - and work from there.