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New homeowner of a 1944 house here. My AC is assaulting some of my house and is barely leaking out of the vents in other rooms. Particularly one bedroom is not getting any cooling. I took off the vent and can't feel any obstructions.

I found some strange levers on the ceiling in my basement on the ducts that come from the boiler unit and they are turned all which ways:

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I tried having someone stand near various vents and turning them all which ways, but she couldn't really tell an effect for most of them. The one labeled MBR definitely controls the master bedroom and when I turn it the airflow drops out of the bedroom, but it doesn't show up in the other two bedrooms.

What direction should these levers be in? Is it "closed or not closed" or is it finer grained than that? How can I deterministically tell what these do?

  • I just ran into this with my 1955 house - my bathroom was getting no airflow. However, my ducts only have wingnuts, no handles. I loosened the wingnut and turned the threaded end with a needlenose pliers, and voila! Airflow restored. – mskfisher Mar 16 at 21:14
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Those levers control a flap inside the duct. If the handle is parallel with the duct, it is fully open. If it is perpendicular to the duct, it's fully closed. And you can set it anywhere in between to fine tune the flow.

If you have an area that you never use, you can close it off to save on the utility bills. But don't completely close it because you want some amount of air circulation so it doesn't get musty. You can also manipulate what is fully open and what is partially open to do more work in selected areas. As Ed Beal points out, some systems are designed around one part of the house getting more flow than another, like a 60/40 split, and that mix being seasonally adjusted.

However, the heating and cooling system is designed around exchanging heat with a certain volume of air moving through it. If you block significant air flow so less total air than intended is moving through the air handler, the system's operation will be less than optimal. You could even stress the equipment if you block too much.

Sometimes, the system isn't well designed, and a room far from the air handler just doesn't get a lot of air flow. It can be helpful to add a small vent fan in that room to pull more air. I've used a little add-on fan like this and it helped a bit:

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    Without seeing the system we cannot say they all should be open. Many 2 story homes have dampers for each floor and a 60 / 40 split is normal 60% upstairs when AC is on in the summer and 60% downstairs when the heat is on in the winter. A 60/40 split keeps areas from being stagnant and is overall the most efficient with a properly sized system. – Ed Beal Jun 15 '17 at 22:17
  • @EdBeal, good point. I was thinking just in terms of the system not being designed around part of the house being shut off. I'll clarify. – fixer1234 Jun 15 '17 at 22:20
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The levers are "Balancing Dampers". You can balance the system by loosening the wing-nut and moving the damper to block air from a room that is getting too much air and allow air into another room. (Be sure to re-tighten the wing-nuts so they don't move over time.) Use a pen to mark the location of the damper blades...with a date. It's trial and error, but you can improve the air (thus temperature and comfort level) in each room over time.

The installer was nice enough to label the ducts for you: DR = dining room, MBR = master bedroom, LR = living room.

The unit puts out a certain amount of air. Your job is to balance the air so it is distributed the best possible.

If you need more air, open the unit's cover and see if there's another pulley. If the pulley is bigger than what the unit is using now, you could move the fan belt to the bigger pulley. This will cause the pulley to spin faster and you'll increase the total air flow. (Also, make sure the pulley are tight to the shaft. If they are loose and spin, you'll loose air flow.)

  • but I have more rooms than that. Specifically the MBR is getting too much AC but two of the other bedrooms are starved, so where are the levers for those rooms? – Tommy Jun 16 '17 at 12:26
  • They don't send an individual duct to each room (like an octopus). Rather, they group rooms together and send ducts out with branches to smaller rooms, (think of a tree). – Lee Sam Jun 16 '17 at 13:20
  • To determine which rooms are controlled by which lever you can close two of the levers and then check the rooms to see which ones have air flow. Do that for all three levers and you'll have a map of which rooms are controlled by which lever. If you see a pattern that all the rooms on one lever are too cool or not cool enough then you can experiment by adjusting the levers. You can fine tune it further by closing the vent in a particular room if it is too cold. – Platinum Goose Jun 16 '17 at 15:43

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