Re-routing HVAC

drfrankencopter · Post by **drfrankencopter** » Thu Jun 16, 2005 10:57 am

I've got a couple of 7" round ducts in my basement that I'd like to re-route so that they travel between the joists, rather than directly below them. This will greatly simplify me ceiling installation. Currently, it looks like the only thing preventing this is the solid blocking that has been placed between some of my joists. Can the blocking be removed, and replaced with an alternative brace (perhaps a hollow square, or just a cross brace at the top and bottom of the joists)?

Is it better to be talking to HVAC contractors, or general contractors for this?

Cheers,

Kris

PS: I can provide photos if required....

knightfly · Post by **knightfly** » Thu Jun 16, 2005 3:16 pm

Kris, what's the actual height and width of your joist cavities?

Will this round duct feed your studio, or is it just passing thru on its way to the other parts of the house?

If the ducting is for studio air, you may want to consider running TWO ducts, one thru each side of an "X" brace, in order to get a large enough cross-sectional area to slow the air VELOCITY down; this will make a HUGE difference in the air noise, since noise level due to moving air is roughly proportional to the 4th or 5th POWER of the velocity.

Changing the blocking from solid to X bracing should only require a hammer and pry bar, and a screw driver to put in the metal X brace; if you use flex duct, be sure and watch NOT to let it "kink" or lay flat around turns - that's one problem with that stuff, and it will reduce air flow AND increase air velocity past the restriction, making more noise.

If the kink happens within about 15 feet of the outlet, you will hear the increased noise at the register (as well as getting less air flow)

Those braces are there to keep the floor joists from twisting under load, but taking one out and replacing it before taking out the next one won't cause any problems.

If you don't want to do the ducting yourself, I'd say HVAC guy; as I mentioned, it's hardly worth getting a GC out there for the brace change, and a GC will only call an HVAC guy and charge you for doing it... Steve

drfrankencopter · Post by **drfrankencopter** » Thu Jun 16, 2005 10:06 pm

Hi Steve,

A few short answers to your questions.

1. Height and width of the joist cavities. Well, the depth is about 9", and the spaceing is quite variable across the width of my basement. In the tightest spots, where one HVAC line lies, there is about a 12" spacing, in other spots, more like 20".

2. The ductwork in question feeds the rest of the house...studio air is something I'll have to tackle a little later...and probably will need some kind of seperate air handling, at least for cooling and ventilation.

In order to fit the duct, I'll need to remove the blocking, but I can't justreplace it with an X brace...it just won't fit (unless I X brace parallel to the bottom of the joists rather than perpendicular). I was thinking of using a box section (rectangular peice of wood with a cutout in the center to allow the duct to pass), or using wood strapping anong the top and bottom of the joist to provide the stiffness against twisting (which is why I assume the blocking is there in the first place). The blocking that's there right now can't be doing too much in the center area since my joists are engineered, and there is no contact between the center of the joist and the blocking material.

Cheers,

Kris

knightfly · Post by **knightfly** » Fri Jun 17, 2005 2:21 am

What about just moving any blocking in the specific joist cavity you will use for ducting, sideways into the neighboring cavity? This would maintain twist resistance, and give you a clear run... Steve

drfrankencopter · Post by **drfrankencopter** » Fri Jun 17, 2005 2:50 am

Interesting concept....there is blocking in both adjacent cavities currently. Probably overkill, but maybe it's because the joists are doubled in this particular area.

Kris