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Install & Replace

Adding a ceiling register to trunk in basement of split level

This is the basement of my 1970's split level. I was hoping to add a heat register to the trunk that is now encased in soffit framing. The prior homeowners had a drop ceiling and had the grill attached directly to the ceiling tiles which were butted against the trunk (and not sealed, imagine the air leakage!) I was hoping to seal the old hole, cut a new hole, buy some sort of short collar that would fit both the trunk side and the grill side...then buy an adjustable vented grill to control the air flow as to not disrupt the heat flow to the upstairs. Can I make something with duct board and duct tape on the trunk side? If so, how can I attach the grill on the drywall side, screw it directly to the drywall? Thanks! gia

soffit duct.jpg

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Posted 2012-12-30T14:43:47+0000  by e4rthmoth3r e4rthmoth3r


Hi Gia,


It sounds like you are on the right track already.


You really don’t need a collar fitting to make a transition from the trunk to the ceiling register. All you need to do is bend the sides of the opening, on the trunk, to where sheet metal folds to over the soffit framing.


Just like this;

register drawing.jpg


register cutout.jpg

Open corners can be taped or closed off using scrap pieces of sheet metal....


Installers normally avoid registers right of the main trunk. It has to do with noise and air velocity.

Because of that it is difficult to find the starting collar that will match the base of the typical 6x10 or 6x12 three or two way ceiling register.


Grill is normally screwed in to transition itself by notching and folding the sides of the boot.


register cutout2.jpg

Hope this helps and please do not hestiate to post back with any further questions you may have.



Posted 2012-12-31T20:44:23+0000  by George_HD_CHI

George! Thanks so much for the quick response WITH diagrams!! I remodel on my days off... While configuring the new ducts downstairs, I've detached and patched the existing ductwork. Which was added in 2004 by the date stamped in the rigid metal ductwork.


AMAZING how much heat flows upstairs now:) After your thoughtful post, I'm considering running a branch from the trunk instead of a register off the trunk. I think we'll get more even airflow. The old configuration had a 'branch off a branch'. The direct branch off the trunk fed the upstairs dining room. In order to heat the bedroom downstairs, they branched off that branch. There is also the register off the trunk we already discussed and a branch off the trunk that feeds the bath down there.


The branch off the branch for the downstairs bedroom was closer to the trunk than the one that turns upwards to feed the dining room; the air flow upstairs barely moved as a result and it rushed through the vent in the bedroom. I think If I run a branch from the trunk to the bedroom and another branch from the trunk to the living area, it should distribute the heat more evenly between floors? Rather than branching off a branch.


With the old configuration, it's cooler downstairs but livable (WA state so moderate winters mostly). I'd like a reduction in the rushing air flow through some vents and not in others.


Thanks again,


Posted 2013-01-01T13:51:17+0000  by e4rthmoth3r

Hello again and sorry for the delay :(


Gia taping in to the existing branch or branching off the dedicated branch is a big no no.


This can be done on the main trunks using Y profile, but with the dedicated supplies -that are normally sized based on the room volume, this will result in an even air flow that you're experiencing right now.


Branch that is closer to the main trunk is going to get significantly more airflow that the, for instance, register at the very end of the branch.


Your very best option is to tap in to the top or side of the main trunk.

Transition is achieved using the fitting called take- offs, which are available in side and top versions.


Here's the link to the product page on our site.


You're probably going to have to tap in to the side of the trunk, considering you really have no room to cut the opening at the top.


Once the take-off fitting is installed you're also going to need to install something called damper. A damper is basically a round plate that is installed inside the pipe and it comes with the lever that allows you to adjust the flow going in to the pipe.


Now you're thinking; "Well I can adjust the flow at the register" - you can but this will reduce the air flow to the upstairs and result in that whistling sound at the register grate.


What else...


Supply pipe are sized based on the square footage. Rule of thumb is to have 1 -1.25cfm (cubic feet per minume)of the conditioned air per 1 square ft. of the conditioned space.


A 6' solid pipe can supply up to 110 cfms of air. This is normally what you will find in an average bedroom. If you need more that 110 cfm, you’d install an additional supply rather than going with the bigger pipe.


Place the register / boot close to the outside wall/windows, this way you will utilize the conditioned air at its maximum.


Hope this helps and again sorry for the delay.





Posted 2013-01-29T17:10:46+0000  by George_HD_CHI
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