Gas Fireplace using Class A vent

The home I inspected today use to have a wood burning stove. A class A vent is installed. A free standing gas fireplace has replaced the wood burning. The gas fireplace vents into the Class A vent. Is this ok. I understand Class A is generally used for high temperature fuels such as wood or oil. Since the class A is designed for high temperatures is there any reason why it could not be used for gas which is cooler. I feel as though it is ok but as you see in the left side of the photo, the neighbors had the same conversion and their installer ran a B vent through the Class A.

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He did that not because of temp but because diameter should be sized to btu output for proper drafting.

ok. Since B vents are usually 3-6 diameter, the 8 inch class A is probably larger than desired for gas appliances and may not draft properly. Sounds like I should refer them to a fireplace installer.

I noticed in my travels around town today this appears to be a common occurrence in older buildings where wood has been converted to gas. Is this something you always call out or only if the fireplace appears to be drafting poorly. Due to the number of these types of installations done improperly I am wondering if the industry views this as a material defect or “not a big deal”

I am certain it goes uncalled many times ,but you should call it out.

Agreed. Thanks

Even if it is a clay tile flue the gas can eat at the mortar between sections and should have the B vent.

Report language is up to you but perhaps a few guys will chime in on how tough it should be in their opinions.