Studio HVAC: All about mini-split systems, HRV's and ERV's.

#31

This has been a really informative thread. One other question if you don't mind - of the "devil in the details" variety.

I attached a video of a standard minisplit installation as an example. Just watching that, I'm trying to figure out how one would seal two holes in a double wall from the line set without trashing the isolation.

My guess is that you would do the following:

Wrap the line set tightly with electrical tape,
Drill the two holes offset from each other by a few feet.
Bend the line set accordingly (very carefully as some of these are kink-able copper lines).
Weave it through both holes somehow -- this seems like the hardest part, given that there is a bunch of insulation in the wall too.
Seal both holes with caulk or putty.

Do I have that right? It seems like you still wouldn't have a tight seal after all that, due to the multiple lines bound together. Small airgaps inside the line set would be unavoidable. Also, if you ever had problems with this minisplit in the future, you might never get it out of the wall. Finally, it seems pretty unlikely you would ever find an HVAC tech who would take the time to do it this way. DIY seems unavoidable.

Perhaps I'm overthinking this. Is there a better way? It seems just about everyone is doing minisplits in the room these days.

https://www.youtube.com/watch?v=ozaw9QhxkQU

#32

use a decoupled conduit (S shape if you will) to provide the offset path between the walls. use this method for plumbing (like the refrigerant lines), audio wiring, etc. this is installed during the build so not need to chop things up later. once you route things through your conduits, seal the ends with putty pads.

#33

I'd just like to echo everyone's compliments as well, brilliant explanations!

#34

Hi all, I have another relevant question. A lot of HVAC designs involve silencers in each leaf connected by duct inside the gap between walls or ceiling. I know it's recommended to use flex-duct here to avoid a hard connection between leaves. As I'm looking at my own design, it occurs to me that, once the walls are closed up, it will be very difficult to get in there ever again. The flex-duct I have experience with is made of a very thin plastic material, with metal coiled around it and foil covered insulation over that. This duct, when used in attics and basements, is known to fail and fall apart over time -- although more often than not, due to extreme temperatures and rodents, etc. The point being that those areas are accessible to replace ductwork when necessary.

In my situation, I would think that space inside the walls will remain virtually undisturbed forever. So my question is, do you think it's safe to use this kind of "standard" flex-duct between walls or is there a more robust alternative that you'd suggest? Here's an example of something that appears tougher, although you really can't be certain without a 15 year test...

Here is another one, although I've heard mixed reviews about foil based duct. Seems it could be more prone to cracking open than the plastic.

#35

another option is to nest a set of hard insulated duct - typ these have 1" (25mm) insulation inside the hard duct exterior (e.g. duct board). so a duct with an exterior of 8" x 8" inserted into a 10" x 10" duct - and seal the exposed insulation edge. each sleeve is short by 1" and you have a decoupled hard duct. each side is just shy of connecting to the opposing surface and the "soft(er)" insulation minimises transfer. the best bet (i use) is to make this arrangement from duct board as it becomes easier to create proper sizes which behave as expected versus trying to use fixed commercial duct sections.

#36

Thanks, that would work in some situations. For me, the two silencers would be offset from each other, both vertically and laterally. So I definitely need something flexible. The distance is about 4ft and crosses a couple studs to get from one to the other.

Here's an example. I think it's a pretty common scenario where things don't line up at all. I don't think the insulated duct is necessary as there will be insulation in the wall. I just want something I can count on being durable.

#37

one option for flex duct is to nest a smaller duct in a larger one and use a plenum to expand the volume (reduce air velocity) from a smaller duct cross-section.

#38

This seems needlessly complex for such a short run. Space is very tight as you can see from the pic, and the geometry is not friendly. Do you think standard flexduct is durable enough to seal up like that and, if you wouldn't trust it, can you recommend another round, flexible duct that you would trust?

#39

i've not had a problem with good quality flexible duct in over 20 years of using it. but the reference to nesting it is to address the concern raised that it might not be durable enough. i don't use flexible duct when i can use hard ducts and generally use the nested hard duct approach in most cases, but sometimes only a flex duct will do it (a recent studio in Brooklyn) where i needed the flex duct to traverse a long isolation soffit and branch into the in-room silencers and plenums. i don't have any worries this will continue to work for many many years as the air velocity and pressure levels are set as low as we can go to address the air exchange and other hvac requirements, so wear and tear will be minimal.

#40

Thanks, I'm glad to hear that. It didn't seem likely that something that's virtually hermitically sealed would be prone to failure at such low pressures. If you don't mind I drag this out just a bit more, would you consider something like Master Flow (which is sold at big box stores) to be good quality flex duct?

https://www.homedepot.com/p/Master-Flow ... /100396936

I've been looking for something "better" but that's were we can get into borderline unobtanium for DIYers. I sent an email to Novaflex asking for a recommendation, but then again, maybe the Master Flow is sufficient.

https://www.novaflex.com/productcart/pc ... ng-c32.htm

#41

i think in general the big box store flex duct should do it, but if you can go to the store and "feel" it and perhaps visit a specialty store and see what the expensive stuff is like (e.g. tougher exterior sheathing, some more rigid interior etc), it will let you decide.

#42

gullfo wrote:Source of the post use a decoupled conduit (S shape if you will) to provide the offset path between the walls. use this method for plumbing (like the refrigerant lines), audio wiring, etc. this is installed during the build so not need to chop things up later. once you route things through your conduits, seal the ends with putty pads.

Do you have any pictures of this S shape conduit setup?

#43

I've been reading the Sound and Vibration Control chapter from the ASHRAE Handbook.

ASHRAE-HANDBOOK-Sound-and-Vibration-Control.pdf: (5.32 MiB) Downloaded 1129 times

ASHRAE-HANDBOOK-Sound-and-Vibration-Control.pdf: (5.32 MiB) Downloaded 1129 times

Some really good useful information here highly relevant to this topic.

#44

here's one. each pvc (or metal) are secured to their respective wall, and then using a rubber coupler (as soft as possible) to bring the 25mm-50mm gap between them.

#45

Great method! Thanks for the picture.

Soundman2020 - Studio Design Forum