Replacing Section of Sheet Metal Trunk Line With Flex Tubing

Hi,
I have a split/tri-level house and am trying to put a shower in the basement where a 1/2 bath alread exists. I ripped out the walls and the ceiling in the bathroom and found that the main HVAC supply trunk goes from the air handler just outside the bathroom, above the ceiling and down the back wall of the bathroom. The trunk does a 45 degree angle from the ceiling at a downward angle at the end of the bathroom behind a fake wall setup to hide the duct, goes down behind the wall and does another 45 degree angle travelling the same direction out of the bottom of the bathroom wall. It goes through an opening in the cinder block foundation out under the other side of my house that only has one level (the bathroom is just on the other side in the downstairs level if that makes sense). This trunk then supplies a kitchen and a family room.
My HVAC problem is that where they did these 45 degree bends was not in one isolated corner of the bathroom or the other but about a foot or so away from the corner. Ideally if I could take out the whole duct and use this space for my shower I would be set but of course then I wouldn't have HVAC in my kitchen or family room. Plan B would be to move or replace a small section of the duct beginning in the ceiling, move it over as tight into the corner as possible and then just build a very small L shaped wall to hide the duct in the corner. This would give me an extra foot or so width for my shower. I shouldn't have a problem cutting through the cinder block but I was hoping that I could cut the exisitng sheet metal duct from somewhere in the ceiling and replace just a section of it with flexible duct. This short flexible duct would then be spliced back into the existing sheet metal duct work under the house. I am guessing the run would be no longer than 10ft. Is splicing flexible duct doable or should I replace this section with matching rigid sheet metal duct? The run from the air handler to my kitchen is 8 ft at the most, but the bend going down the wall adds to this length. The kitchen and livng room area are at the most 500 sq ft. There is a separate trunk handling that won't be touched handling the rest of the house. Thanks in advance!
Mark
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snipped-for-privacy@vhda.com wrote:

Unknown to the average homeowner, flexible duct offers *more* resistance to airflow than straight sheet metal by one size or more. In other words, a 12" steel duct would have the same airflow as a 14" flex. Understand though, the newer flexible duct really isn't that flexible in the sense that you can't make it square. And flexible duct doesn't like making quick turns like sheet metal can [with turning vanes.] And, if you take flexible duct vertical, that it has a tendency to "pull" on the connections and it can come apart where sheet metal is [screwed] or has mechanical drives holding it in place. Sheet metal duct is more costly [especially special made to fit sizes]. But it will out last.
You might be better off seeking some outside HVAC help here.
--
Zyp



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