Mr. Heater 4 Inch Horizontal Vent Kit for Big Maxx MHU45LP, MHU45NG, MHU75LP and MHU75NG Unit Heaters #F102845 F102845 vent kit Used for horixontal venting on MHU45 heaters Used for horixontal venting on MHU75 heaters Maintains proper clearances through combustible construction May require additional parts to meet local codes