GPS·H allows the conversion of ellipsoidal heights h, that are either NAD83 (CSRS) or ITRF, to orthometric heights H (heights above mean sea level) by using a gravimetric or hybrid geoid model. CGG2013 and HTv2_0 convert to CGVD2013 and CGVD28, respectively. The other geoid models do not convert to either CGVD2013 or CGVD28, but to their own reference system.
The on-line version accepts the following types of input coordinates: geographic, Cartesian and UTM/MTM/Stereographic. By clicking the "Batch Processing" box, you can submit coordinates in a file. The "Input H" box is for the reversed conversion (H to h).
View documentation for GPS·H