I was in a crawl space, the duct has about a 12 inch diameter opening on top as seen on the right side of the photo. There is air flowing out of it.
This is a vented crawl space, the open is about 75’ direct opposite of the furnace itself. I recommended the home owner contact an HVAC guy for evaluation.
He stated it’s a common building practice in my area. I called my HVAC guy and stated it’s not correct.
My thoughts are this large opening is providing moisture to a vented crawlspace potentially creating an environment for mold. The open is reducing air volume to supply registers. The homeowner is spending extra energy/money needlessly heating/cooling the already vented crawlspace.
I was reading through articles in the NACHI library but could find a direct article. Any have a good resources for education? Please provide a hyper link. I’d like to learn more.