Hi, thanks for allowing me to become a member. Here is the problem. I have a split unit for 2nd floor, 1.5 ton. the furnace is in the crawl space connect w/ 2 of 12" duct (supply & return) to the attic, about 35' long. a plenum box, in attic for supply, has 9 of 6" duct to all rooms. only 1 return grill size 24"x12". there is almost no air in supply. I need to place my hand 2" from the register to feel the air. return air too weak can not hold a pc of toilet paper. I checked the return duct in the attic & found it broken half way. to fix temporarily at 9 PM, I rolled aluminum sheet into 10" pipe and connect it. I immediately notice a strong suction at the return grill. a week later, I replaced with a new 12" duct and the force gone away, back to the previous problem. I contacted contractor and was told there was no return air for unit to supply. he opened the side wall of the furnace at the return end and a strong blow at the supply end. when closing the side wall back, the blow at supply furnace gone. he did not see any leak so he suggested I change the return duct from 12" to 14" or 16". anyone had this problem please share? is there anything else I need to check? I can not spend too much money and hoping that upsizing the return duct will fix the problem. Thanks in advance.
No air
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Hi beenthere, thanks for the recommendation. Since the main return grill is at the middle of the main hall that has a plenum box above the filter and I also always want to add another return grill, can I leave the existing filter alone 24"x12" and add another return grill at the end of the hall? All I have to do is to cut the hole at the plenum box and run a duct to the new grill. If it is doable, what is the duct size and filter size? My thought is 6" flex duct with a smallest filter size. Again, thanks for the recommendation.
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