HVAC guy here. Looks like the Microwave vent was added either as a renovation or as a last minute fix during construction. It should be buried in the studying, not sitting atop it. That vent won't reach high temperatures at all, so any sealant is fine. Depending on your climate, insulating the vent with pink fibreglass could be a good idea. #1 to prevent condensation dripping down the wall cavity and growing mold and #2 for heat loss.
RandallBagsyFoot t1_iug8rrn wrote
Reply to Insulation around Microwave hood vent by RatArmy
HVAC guy here. Looks like the Microwave vent was added either as a renovation or as a last minute fix during construction. It should be buried in the studying, not sitting atop it. That vent won't reach high temperatures at all, so any sealant is fine. Depending on your climate, insulating the vent with pink fibreglass could be a good idea. #1 to prevent condensation dripping down the wall cavity and growing mold and #2 for heat loss.
***Ah, "newly installed microwave" I see.