LINAC4 [1] is part of the CERN LHC injector chain upgrade and will accelerate H ions from 45 keV to 160 MeV. A movable diagnostics test bench will be used to adjust the machine parameters during different stages of installation. One of the main instruments on this movable bench is a transverse emittance meter. Given the beam properties at 3 MeV and 12 MeV, the slit-grid system already developed for the measurements of the transverse emittance of the 45 keV H source will not be suitable, mainly due to the high thermal load on the steel slit already with a single LINAC4 pulse. For this reason a new slit has been designed based on analytical and numerical simulations for different materials and geometries. The energy deposition patterns for the different cases have been simulated using FLUKA [2] and will be presented in detail. In addition, the choice of wires for the SEM grid will be discussed, in terms of material, diameter and spacing required, to achieve the required measurement accuracy.