Jon, from what I can see, the first unit is a factory built fireplace. Please, everyone eradicate that term "zero clearance" from their lexicon. You would need to find the rating plate to identify the make, model, serial number and listing number such as UL127. The chimney must be listed for use with this fireplace, which, btw, if a 127 box, would need to be installed into framing and not have the unit exposed like that.

The second unit appears to be a see thru, which usually do vent out one end. The type of venting is dictated by the listed instructions so don't guess. There are gas fireplaces listed for use with flex venting.

The heights of those vents and chimneys are determined first by the listing then the codes. Vents do not have the same 3/2/10 rule as chimneys. That looks like a Metalbestos factory built chimney, which would need to meet 3/2/10. The proximity of the vent to the chimney would be determined by the vent listing. I would want to make sure that vent termination was listed for a vertical application. The storm collars need to be caulked. You need to know if those roof flashings need to be vented. They may have installed an unlisted flashing so check the manual.

The best answer here is, of course to get a Level II inspection by a hearth pro. In this case, you would hope to get one NFI Certified in gas and wood as well as other credentials such as FIRE or CSIA.
HTH,
Bob

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