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My HVAC system consists of a fan, furnace, compressor-driven AC, and evaporative cooler. The problem is that there is a large air volume used only by the evaporative cooler that is generating a lot of turbulence as air flows by (think blowing over an open bottle).

I want to install a damper to close off this useless and turbulent air volume when the evaporative cooler is not running.

My question is: Can a (motorized?) damper be installed within the existing ductwork? Does such a device exist? Or does the motor always have to be external to the ductwork, and thus I have to remove some ductwork to install a damper? Is there a non-motorized, manually-operated damper that can be installed within the existing ductwork?

The ductwork is rectangular sheet-metal ductwork, about 2ft by 2ft cross section (not sure on terminology), perhaps 2-3ft high.

I am open to other ideas on how to close off this air volume.

A schematic is shown below:

Before

enter image description here

After installing a damper. Preferably this damper is motorized and electronically-controllable.

enter image description here

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    There are dampers that can do this you will probably need to remove the cooler to install. Do you have access to the duct work at that corner? The actuator will normally be external to the duct. If you don't plan on opening /closing more than a few times a year I would install a manual hand operated damper I find the powered ones if not used often fail fairly often. A smoke damper for normal use with a fire alarm work forever but are way more expensive. – Ed Beal Aug 3 '18 at 13:51
  • @EdBeal The "easiest" access I have is to remove the evaporative cooler on the roof, I think. Also I agree with you about manual vs motorized reliability. Maybe a manually-operated one installed within the existing ductwork is a good solution. Now where to find one... – OrangeSherbet Aug 4 '18 at 8:24
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    Several times I have had custom ones made for under 50$ (mechanical single plate style) powered ones are closer to 150$ and listed smoke dampers are up in the 400-500 range. A local shop that installs furnaces is a good place to start If you need a custom size, the internet is cheaper if you have a standard size. Measure the duct and look for dampers, or smoke dampers and will be lots of options, easy to install manual models drill the hole for the square shaft to come through the duct wall, slide it in place and screw in place. – Ed Beal Aug 4 '18 at 15:46
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Try looking up belimo motorized dampers. They are excellent dampers, hopefully they are available in your area.

This is a Belimo damper actuatorenter image description hereBelimo

This is just an example. They do have less expensive ones. You'll need get a sheet metal shop to make the damper for you. You need to be very specific about the sizes and dimensions. If you don't use the right terminology they may get upset. You will probably need to use whatever damper actuators they stock.

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