I have a register in one of the rooms where the heat blasts at really high velocity and it gets incredibly hot in the winter (80+). My son has been complaining for years and I can’t seem to find the right way to divert the flow away from that room. The rest of the registers that happen to be further or closer than this one seem to receive an acceptable volume and the temp distribution is fine everywhere else.

The problem register is 12x12, where as the other registers on the floor are 10x10.

What would you advise I can do?

Here are some pictures of the ducts: enter image description here offending duct register

  • 7
    Doesn't the register have a restrictor adjustment screw? All the registers in our 1970 tract house have them. There is one room in particular where I change the amount of restriction depending on whether we are cooling or heating. Nov 30, 2021 at 12:09
  • 1
    @JACK I added pic of the register. One problem i've had previously (I changed the whole upstairs hvac unit last year), if I closed down the register a little too much, the old furnace used to shutdown. I was told that some vaccum tube was triggering the shutdown. It hasn't happened with the new unit. But I was thinking there must be an amount of air that the heater has to cycle thru, and the number of registeres is right at the minimum per the tonnage?? I'm not sure.
    – Elijah
    Nov 30, 2021 at 14:50
  • 3
    Be sure the vents in all the other rooms are wide open. You shouldn't have a backpressure problem from closing down this one.
    – isherwood
    Nov 30, 2021 at 15:28
  • 3
    I'd experiment adjusting the register before making any other modifications. There's a reason that lever is there. It looks like a nice job on the install, I'd wait before changing it.
    – JACK
    Nov 30, 2021 at 15:38

3 Answers 3


For a quick and inexpensive solution lay a piece of cardboard on the vent which covers 50-75% of the area. Adjust size as needed.

  • 1
    @Elijah cardboard will be fine for a quick test. You can use that to prototype the size and configuration of the damper: start with a piece cut to the exact size/shape of the register (100% blocking) and cut away 2/3 of it (based on a 12x12 register being 144in² vs 10x10 being 100in²). If it blocks too much, cut away more until you get the desired effect. Once you have a good size/shape that works, use the cardboard as a template to cut your sheet metal for a more permanent damper.
    – Doktor J
    Nov 30, 2021 at 15:07
  • 12
    No furnace puts out heat sufficient to ignite paper. If so you'd smell smoke as the dust in your ducts burns away. There's a big gap between ouch and fire.
    – isherwood
    Nov 30, 2021 at 15:27
  • 1
    Other options could include a brick, or a suitably-sized dinner plate or drinking mug. Crockery/porcelain will absolutely take the heat fine. If the weight on the grille is too much, push it into the pipe some so the weight is on a rafter.
    – Criggie
    Dec 1, 2021 at 2:04

As another option you could install a grille with a hole pattern to reduce the effective opening.

Smaller holes will constrict the flow so the choice of the size will control the heat output - note that this may cause changes on the others as well.

But an advantage is that the existing installation does not change or cause changes to the decoration.


If volume is the problem you can

  1. change the duct, boot, register, etc. to match the others. (Make sure the the new duct branches off the main duct in the same manner as the others.)

  2. Install a manual volume damper. You’ll probably need to replace the duct leading to the existing register because I’ve never seen one installed in a round duct. However, the advantage of this option is that you can adjust it over time and over seasons (summer and winter).

  • 1
    Dampers are certainly available in round duct, often as part of a takeoff.
    – Glen Yates
    Nov 30, 2021 at 14:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.