I paid extra money to have my microhood vented outside. The vent is a 3 1/4 X 10, which converts to a 4" and vents outside the townhouse.

Everything I read states that it must be at least a 6" round to get the proper CFM. The HVAC guy showed up today and is in total disagreement. He stated it must be a 4" round to accomplish the proper CFM, and that if we put in a 6", it will create outside air infiltrate and turn the microhood into a refrigerator.

I think he does not want to fix it. I showed him the manual from GE hoodvent originally placed at build - then I showed him the paperwork for my new Microhood. Apparently, he thinks he is smarter than the average bear.

What do you think? Is 4" going to give me the proper CFM to run the microhood? Is a 6" going to turn my microhood into a refrigerator?

Please advise. Thanks

Install all equipment to the manufactures instructions and you should not have any problems. Sounds like the HVAC guy is trying to take the easy way out.