The code for chimneys for gas fireplaces says the chimney going floor to floor over 4 stories must be in a two hour wall. What about horizontal? When the vent leaves the fireplace and connects to the riser the code does not spell out if the horizontal portion has to be rated. I know fire wrap is not legal is there any other wrap that is? Also the installation instructions say no insulation should cover the pipe. Does this mean calcium silicate is not legal?