for emergency use remember to open the kitchen window an inch or two
and turn on the unvented natural gas oven with the oven door closed and
battery operated CO detectors tested and working.

your existing fireplace may just be rated as decorative.
vented natural gas heat is always required to avoid health problems
including asthma.
inserts are made in many different sizes, you'll want to get the
largest BTU that will fit into the fireplace opening size.