# Moving ductwork to accomodate a finished basement



## Badfish740 (Jan 13, 2010)

We have a 1200 SF two bedroom 1 bath ranch with a full basement that was partially finished by the previous owner into an office space.  The walls were fully finished (framing, vapor barrier, insulation, drywall, etc...) but there was never any carpeting and a drop ceiling had been installed.  It was a usable space but we would like to turn it into a combination family room and office.  The major obstacle to making the space really "feel" finished is the ductwork, which like in many homes, runs off of a central trunk line which is routed down the center of the house with the furnace at one end.  In my case it runs perpendicular to my basement stairs so that in its current configuration, once you reach the bottom of the steps the supply and return are directly above your head and clearance is about 6' 1" which is claustrophobic for my wife and I both at 5' 10" and an actual obstacle for some of our family members who are 6' 2" and taller.  In any event, having the ductwork there and not being able to enclose it will definitely detract from the finished product, so I am committed to moving it somehow.

First it would be helpful to establish what I have so here are two pictures taken from roughly the center of the basement looking toward the outer walls at the ductwork:







In the above photo I'm standing near the basement steps (they are white and can be seen in the lower left corner of the photo) looking toward the furnace.  You can also see my ESW add-on furnace which is actually our primary source of heat unless we're away from home for an extended period.  I should also add that we have central air.  The next photo was taken from the same spot facing the opposite direction toward the end of the run:






The supply is on the right and the return is on the left.  Both ducts start out as rectangular 8" x 18" and then reduce (the return reduces before the supply) to 8" x 8".  Hot air is carried from the main trunk to the registers by 6" round duct.  The supply ducts are simply spaces between the joists enclosed by stapling sheet metal over them to form a conduit for air.  This can be seen clearly in the second photo.  Because it may be hard to visualize the system in it's entirely I've also created a diagram of the system as it is now (attachment D_1) and a diagram of what I envision as the solution (D_2).  *Note to Hearth.com users-this site does not support .pdf files so I could not attach them.  You can view them here.*

Basically my idea involves shortening the main trunk lines so that they end just before reaching the basement stairs where they will be capped and hidden by a wall.  The difficulty of course is the fact past that point there are four registers, two for the kitchen and two for the living room.  Currently there are also two returns in the living room as well, but I am not as concerned about them for a few reasons.  First, there is a central 14" x 14" return vent in the hallway leading out of the living room to the bedrooms, and each bedroom has it's own return, all of which would be retained.  Second, there are no barriers to air movement between the central return and the living room at all.  In fact, the two living room returns are currently blocked by a couch because there is no other good place to put it and heating and cooling do not seem to be affected by this.  Of course, the return seems to be the simple part-it's delivery that I'm worried about.

Shortening the delivery duct would mean that the four registers mentioned above (two living room, two kitchen) would need to be fed by ductwork which is detoured to either side of the finished space.  My thought was to tap four collars into the supply trunk (two on each side) and run 6" round duct perpendicular out to each wall.  Upon reaching the walls the duct would turn 90 degrees and run along the wall to the register.  These runs along the walls could then be covered by a chase, leaving most of the area barrier free except for the girder, but since it's only about 5" wide it's not nearly as obtrusive as the ductwork.  Again, the "before and after" can be viewed in the two attached files.  My main concern is the increase in length for the ductwork that will need to detour the finished areas.  For example, as it stands now, the far rear kitchen register is a 12' 8" run from the main trunk.  My planned detour would increase the run to 28' with a 90 degree bend in the middle.  How this will affect the velocity and temperature of air coming out of the register itself I have no idea-I feel like a degree in fluid dynamics (or at least a few introductory HVAC classes) would be extremely helpful right now. 

I would perform this work myself since the process of it is fairly straightforward and I can obtain the needed materials at cost, but I'm worried about the possibility of ending up with a cold living room and kitchen because of the long runs.  Am I worrying about nothing?  Are there factors I haven't considered?  Is there a better way?


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## Cutter (Jan 13, 2010)

Indeed you do have some challenges there. My first thought is creating a landing on your stairway maybe halfway up and then turning them to the right to avoid the ducts. Secondly, adding that much length to heat runs will surley reduce flow and might increase noise levels. A larger blower fan might be in order. I would consult a HVAC guy to crunch the numbers for you. Third, creating a drop around the duct work only has to lessen the head height by 5/8" if your frameing is brought down to just the bottom of the ducts or the seams where sections are put together.
Good luck   Brad


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## Gooserider (Jan 17, 2010)

Sounds to me like you are talking about both increasing the length of the runs, AND decreasing their size by half (8x8 or 64"² to 6" round or about 28"²) this seems like really bad news to me...  Not a duct expert, but is there any option for using a different size main trunk in the existing configuration - i.e. something shorter but wider so that you have the same effective size, but don't hang down from the ceiling as far?

If nothing else, I'd try to keep the modified runs at an 8x8 cross section, or possibly even bigger, and / or consider whether you might need to add a booster fan to the runs...

Gooserider


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## jimmy dean (Jan 17, 2010)

BADFISH784;
     So... what are you going to do with that carrying beam, you know the one with all those inconvient posts sticking out of the floor. As for resizing/rerouting the ducts.. please reconsider. With longer /lower area runs, even with a good water based duct sealer (not DUCK TAPE!) on all the joints in the system will not supply adiquate heat to those areas you use the most. The kitchen and living rooms. If you have a porch, convert that and pipe heat to that... PLEASE don't mess with what has worked well for many years warming you and your family!
          = Leaky supply ducts blow (ok) leaky return ducts suck (NOT OK)


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## stephenmoore (Jan 17, 2010)

I agree with everyone else, if you are talking that much change with ductwork, you need to consult an installer/expert. IU did a home reno last year where we stripped out the old trunk line and installed a new system in conjunction with an hvac system. It worked well but we had a pro do all of the design. Maybe you can move the new lines back into a corner chase to max out the headroom.


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## raven (Jan 18, 2010)

you may consider not reducing the width of the duct but reducing the height while maintaining the width.  keep your 18 inch width but reduce to 18 by 6 before the steps. this depends on the load after the stairs though. and it looks as though you have at least 2 ra after the steps. you may be able to do the same.its been done. to me it looks like your best option. but hey im over here in ohio so its hard to see the whole pic ...lol


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