Little to no air out of one vent

[pete6032]

Detached single family home with forced air and heat through ductwork. One room in the house has very little air coming out at all, basically a tiny trickle of warm air when furnace is running.

I removed the vent cover today and sent a camera scope down and the duct appears to be unobstructed for the few feet I can see. The majority of ductwork is in the basement ceiling, which is finished, so I can't see a lot of the ductwork. All other rooms on this floor of the house have about 5-10x the amount of air coming through. What is the next step in troubleshooting?

 

[Greenman]

You need to scope the entire duct to look for crushed pipe or a disconnect. But it could very well be poor design, I've seen that a dozen times.

 

[Sukhoi]

Are you missing any pets?

 

[balloonshark]

Does each room have a cold air return or just one central return? Having adequate return air is important. Like when you open one window and can't feel a breeze but open another on the opposite side of the house and you can feel the breeze.

Unless things have changed the warm air duct should get smaller the further it goes from the furnace. Cold air returns are either one size or the duct gets larger the further they go from the furnace. Both being sized correctly is important. The length and size of any flexible air duct runs are also a factor. Excessive bends in duct work are also bad.

 

[jmagg]

If the weak vent is at the end of a run, you may need to balance things by slightly closing the vents before it

 

[pete6032]

You need to scope the entire duct to look for crushed pipe or a disconnect. But it could very well be poor design, I've seen that a dozen times.

Previous owner finished the basement, diy job. I don't know much about how the ductwork is laid out since I can't see it but is it possible the previous owner chose to use the duct for this particular room to also ventilate the entire basement and therefore the amount of air coming out of the vent is greatly reduced?

 

[Greenman]

Previous owner finished the basement, diy job. I don't know much about how the ductwork is laid out since I can't see it but is it possible the previous owner chose to use the duct for this particular room to also ventilate the entire basement and therefore the amount of air coming out of the vent is greatly reduced?

Could very well be the case. Try closing the basement vent and see if that helps.
I've seen some incredibly poor HVAC installations, and some that were so damaged as to be nearly useless.

 

[Paperdoc]

ALSO possible: when previous owner closed up the ceiling, there are DAMPERS in the ductwork you cannot reach now! And one of those controls air to that vent. In my basement the ceiling is suspended tiles so I CAN reach all ductwork, wiring, pipes, etc.

 

[herm0016]

i like to get a house a bit chilly, and then use a thermal imaging camera with the heat blasting to look for hvac problems. you can usually see right through the drywall to find the issues.

 

[dainthomas]

My master is the furthest room from the furnace and has the weakest airflow. I asked the installers to look at everything when I was getting a new furnace installed, and they mentioned the downstairs return is too small for the system (and can't be expanded based on the location), I'd need another one installed upstairs (at considerable cost). So I run an electric heater in there instead.

 

[mindless1]

^ A vent puller grate fan in the room, or pusher fan inline in the duct should help, but of course there might be additional noise.

Another option if the system doesn't overheat is just close or partially close off some of the shorter runs' vents so a larger % makes it to that furthest room.

An electric heater could still make sense if you want the other rooms to drop in temperature when not using them, let then cool down at night and only keep the bedroom warm enough until you get up in the morning, depending on your schedule and the cost of electricity (and assuming the furnace is gas and the gas prices per BTU are lower).