I am preparing the hole for the installation of a built-in gas fire. The fitting dimensions for the fire state that the base has to be 300mm from the floor. Leaving the original fireplace lintel in place, I was hoping to achieve around 290mm. However, the floor is bare cement at the moment and my measurements had not taken the new flooring into account. This is to be a solid wood floor which, with underlay is likely to raise the floor height by 20mm or so. Overall it looks like the base of the fire will be 260mm to 270mm from the floor. Am I going to need more drastic surgery to raise the fire to the correct height of 300mm?