Hi, I have 2 charmglow 10,000 BTU I want to install in my bedrooms.They both have existing lines.The line in my room is situated strangely in the closet,but I assume the
Closet were not built until much later being it is an older house.The line has a cap on it
And it is close to the floor.I would like to put an elbow on it,and add about 3 ft length of black pipe which I will install through the (inside drywall of closet) to the outside which is paneling where I will hang the heater,install an elbow and short nipple,then the gas shutoff valve and last my flex pipe.Will this be OK or against any code since the pipe
Will be that length running in a closet space? Will it have to be rerouted beneath the floor?
Last question is,the line in my daughter's room has a flare on it and capped on the end so I am assuming gas heaters were hooked up directly to flare on the end of this gas pipe
Long ago when it probably were not mandatory.Can I just hook my heater up to flare
Or do I have to remove the flare,install the shutoff on the pipe and then make my connection to the heater which I know is probably going to be correct?

First thing you should do is check with local city/county building inspecters and see what the exact building code is. The can possibly be a little different from area to area,, sounds like you are on the right track,,

((do I have to remove the flare,install the shutoff on the pipe ))

Yes this is what I would do