Hi, any advice would be appreciated. We have a gas furnace about 15 years old in a small attic above our 2nd floor. Our intake is on the second floor ceiling. Hot air is coming out very strong from the upstairs registers and also strong out of 1 of the 4 downstairs registers. The 3 registers that are not blowing any hot air are very close together (downstairs area is only about 700 square feet.)
Could it be as simple as dirty or blocked air ducts? If it was the filter I would think it would affect all registers. I would love advice on what it might be before I have a HVAC service come out.