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Question DetailsAsked on 8/14/2016

Troubleshooting a room with extremely low air flow from vents.Thinking video inspection. Live in Potomac MD. Ideas?

The room is on the 2nd floor, over the kitchen, which the previous owners bumped out and moved vents.

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2 Answers


I presume you have checked registers to see any adjustable ones have not been closed off - and also that there is not plastic sheeting right under the register (held in by it) from a prior duct mold treatment or sealer treatment, which they then forgot to remove. Check both inlet and return registers.

I also assume this room has both an inlet and a return register - if only an inlet register, then unless the door is undercut about 1/2-1" (like bathroom doors are) and not blocked by thick carpet, it has no place to vent the air so inlet flow will be restricted. Try with door open and see if inflow is good - if so, that is your problem. Also, if never worked right, I have seen DIY or economy addition jobs where they mixed up which was supply and which return ducting and put in a single register on the return, thinking it was supply - easy to check that with a piece of thin plastic (make sure it can't get sucked into the register) across it to see which way the airflow is.

Check in the ducting (exposed areas) for a possible damper in the ducts (commonly look about like following link) - may have gotten accidentally closed (or seasonally closed and not reopened), or if motor or solenoid driven the motor/solenoid have have gone out or wiring failed. Also, if motor or solenoid driven, controlled off a separate thermostat for that area, check thermostat is working and does not have dead batteries, and is correctly set for HEAT or A/C.

If this is recent problem and not damper, you can take a small hand mirror and hold it to look in the ducting after removing the registers in the rooms to see if you can see blockage or crimping of the ducts from there - if flex ducts, you might be able to get at the other end to check there too by removing the clamps on one end of the ducting. Whether or not you will be able to see all the way by going in both ends - maybe, maybe not. Might be able to see part way from an intermediate register too.

Otherwise, video inspection sounds like your next step - some Heating and A/C contractors have them, some Air Duct Cleaning companies, in some areas short of bringing someone out quite a distance from a larger city you may have to go with a Sewer and Drain Cleaning company and have them detergent wash their sewer camera first and then use that.

If metal ducts - I would be looking at blocked off registers or a damper. If flex ducting you have to add the possibiliity of it being crimped off or folded somewhere - due to creep because of excess slack, or many brands lose rigidity over time and can crimp off where they sag over supporting straps or wood blocking.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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