The present application relates to an arrangement for reducing thermal energy loss through a sill assembly of the type used with a door or window. The sill assembly includes at least one sill member. The at least one sill member has a hollow region therein. The sill assembly further includes a baffle disposed within the at least one sill member. The baffle spans a length of the at least one sill member and divides the at least one sill member into a plurality of chambers thereby limiting interaction of warmer air and cooler air within the at least one sill member. The baffle reduces heat transfer through the hollow region via convection.