Vent-Free Heater Consideration?

Hi,My mom have an old flame gas heater in one of her bathrooms that she still use for supplementation and were thinking of replacing it with a new model..What are a good reputable brand besides Kozy? They make crackling noises..She also have central heat/air unit(Lenox) about 15 years old and 1 other gas line in a built-in porch.Do the line have to be pressured tested or can the new heater be hooked up to existing since it has been used every season,and for the buit-in porch thinking of going ahead and installing one there but it has not been in use for years.It should be fine to just hook it up since all other lines have no problems to central unit,hot water,bathroom..etc? Thanks Everyone