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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5669
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have an HVAC system that I want to convert to 2 zones. There

Customer Question

I have an HVAC system that I want to convert to 2 zones. There are already manual dampers installed on the system, one damper for upstairs and the other for downstairs. I need info on what motor to get and how to mount it to the current damper so the zone controller can open and close them when needed.
I already have a dual zone controller installed, thermostats installed upstairs and downstairs, and a bypass zone to relieve system pressure is a zone is closed. Adding a motor to the damper is the last part of my install. Here is a picture of what I am working with:
Thank you.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.
Welcome to Just Answer !

There is the impossibly complex way to approach this, and the easy way to approach this..

The easy way is to apply the damper motor that is specified for use with your already purchased system if it will fit the shaft on the existing dampers. My guess is that the reason you asked this question is that the damper motors you have will not fit the shaft on the existing dampers.

Tell me please if that is correct or not, and send me the specifications or a link to the details on the two zone system you have and I can advise you accordingly.

As we go along just keep pressing the 'continue' button until we succeed.
Customer: replied 1 year ago.


I like easy! I have not purchased any motors yet.

The HVAC system is made by Carrier.

The zone controller is made by RCS. The link to it is here:


RCS does make motorized dampers. Here's one:


I am just trying to figure out what to buy and how to attach it.



Expert:  Phil replied 1 year ago.
Hello again ! Thanks for the links

Those are two wire 24 volt damper systems, the damper motor closes when it gets 24 volt ;power to it, and a spring opens the damper when the power is removed.

the specification is "24 volt damper motor, power to close, spring to opsn' Your damper most likely has a 1/4" shaft.... so that any damper motor that accomodates the shaft size of the damper, with a 2 wire 24 volt feed will work... you can mount it so that with the power off the damper is open...and when power is applied the damper closes.

. but we need to confirm the 1/4" shaft size.

The next step is to confirm that your damper shafts are 1/4" square.
All such dampers come with a mounting bracket that allows you to attach it to any square or round duct.

Customer: replied 1 year ago.

Ok great. It it late where I am at. I will hop up in the attic in the morning and measure and get back first thing in the am. Thank you!

Expert:  Phil replied 1 year ago.
Thats a good plan, I will see you tomorrow when I check in.

Customer: replied 1 year ago.

Sorry for the tardy reply. I've been locked out of JustAnswers for the last 12 hours. Here is what I've been trying to send all day....


Good morning,

So the shafts are 1/4" square. The bay where the handle is recessed into is 6" x 4.5" x 3".


Here are some pics:


Expert:  Phil replied 1 year ago.
Hello again!

That Honeywell damper motor I linked to will be your best bet... but difficult mechanically because of the recess. You will simply have to use a short allen wrench to tighten the set screw after you fit the damper motor into the recess

... or.... replace the 1/4" square shaft on the damper itself with a much longer shaft,.. make a flat plate to fit over the 6 x 4.5 inch hole and mount the damper motor to that.

You can buy sheet metal at most hardware stores heavy enough to make such a plate, that would be 20 gage sheet metal, or you can use the more common 24 gage sheet doubled up.

You can also buy 1/4" square shafting at most larger hardware stores.

You can stay in touch as long as necessary on this after rating my service positively.. I will hold the question open for you in that case.

Customer: replied 1 year ago.

Great! A few more questions so I can feel comfortable doing this (refer to previous pics if needed).

1.) Do I do anything to the existing handle? Try to remove it, or I see several screws to this assembly, do I take it apart?

2.) If I mount the motor to a plate over the recess, do I mount the plate to the box? Can I screw into this box?

3.) If I can get it to fit in the recess, what about the anti-rotation shaft? Where to I drill into to set that shaft?

4.) Lastly I can't find where to buy that product. Can you recommend an online store? I did find this. Will it work?:

Expert:  Phil replied 1 year ago.
Hello again, Try to remove only the existing handle and leave the existing 'quadrant' that is attached to the duct that the handle fits onto.

You will have to physically examine this and make up your own mind.. it is a simple arrangement.... you will have to drill the anti rotation hole as described below... and see if it interferes with the damper operation, if so, cutting it off so that it only protrudes through the hole 3/16" of an inch should solve the problem.

There is no cure for the need to experiment a bit in those regards.

If you have to fit a flat plate over the existing recess, make it an inch larger all the way around and attach with 1/2" long sheet metal screws. However even 2 inch long screws should clear any internal parts.

If you use a plate over the existing hole and a longer shaft then locating that hole is done by noticing which position the shaft is in when the damper is closed and which position the shaft is in when the damper is open... and noticing which position the new motor is in when there is no power on the damper motor, and which way it rotates to close.... there is no substitute for making that observation yourself, live, on site... then with that observation made, you can locate the hole that needs to be drilled.

These are one of a kind type custom jobs, there is no substitute for your own on site observations and judgment.



If you have any trouble at all finding that damper motor on their list, use their 'contact us' link and give them a call.

If you wish to rate my service to you positively so far, I will hold this question open so you can follow up on the same dime so to speak as work proceeds


Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5669
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Phil and 3 other HVAC Specialists are ready to help you
Customer: replied 1 year ago.

Thank you! I am very confident in my ability to move forward with this now. I appreciate all the details. It helps a lot! I will have to call Honeywell in the morning as the website found the product, but won't open it when I click. I will report back if any issues. Thanks again!

Expert:  Phil replied 1 year ago.
Thanks for the positive rating and the bonus!

Discuss the details of your square shaft, its dimensions across the flats, with the person you talk to in order to get any adapters you might need, They may have a square shaft coupling you can use also in order to extend the existing shaft.

Often times the young person you talk to will not be fluent with those issues, ask politely if they have an 'old timer' there who can discuss these shaft compatibility and shaft coupling issues with you.

I field fit these sorts of things myself, and use a file sometimes to get a good fit.

Stay in touch

Customer: replied 1 year ago.

Hello Phil,

I called Honeywell this morning and referenced the m847b. The rep couldn't find the product. I gave him the pdf you gave me earlier and he couldn't provide an answer other than their dampers are m847d (discontinued?). After tooling around online for a while I am led back to here. What do you think? Honeywell wouldn't provide me any vendor info and said go through a contractor. :( Thank you.




Expert:  Phil replied 1 year ago.

Hello again, good work.

The chances that damper motor will work are in the 99% range, with a custom fit job like you have however there are always some accommodations that need to be made as discussed earlier.

Stay in touch as necessary.


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