Duct routing

[Vatmax]

Hello all!

Let me start out by telling you that I am not a GC or an HVAC guy. I'm only the homeowner who has hired a GC. I don't know much about running ductwork, accounting for pressure drops or calculating duct sizes.

There is an addition being built on to my house. A new forced air furnace has been installed in the old basement and they are about to begin routing the ducts into the new basement section that will feed heat and A/C to the new basement and the new floor above it. The house is a ranch.

The basement ceiling joists are 11-7/8" truss joists. The ductwork unfortunately has to run perpendicular. The original plan was to have a nice eight-foot ceiling in the new basement but now the new ductwork is going to make that complicated. The drywall finish will have to go around the duct/s either in part or in whole leaving an undesirable finish.

Isn't there any way to run the ducts though the truss joists? Doesn't anybody make some type of bulkhead designed for such a purpose?

Any advice is greatly appreciated!

Thanks!

Jim

[HayZee518]

Check in home depot and see if they have the 12 inch flexible fiberglas ductwork. It's like a large dryer duct with grey colored poly on the outside with a spring inside. See if you can route this between the truss spaces but by no means drill or cut the truss bottoms.

[Hube]

Most ductwork that is installed below the joists should be located tight against a wall if possible. Then the "dropped bulkhead" won't interfere greatly with the headroom, rather than be located in the center of the area.
Without knowing your truss web opening sizes, or the duct size, we cannot advise as to running any duct thru any of the web spaces.
Another way is to use 5" OR 6" Feeder pipes, then the DROP DOWN (Bulkhead) WON'T BE AS DEEP. Good luck...Hube

[LazyPup]

Flexible duct is not recommended for long runs. The duct diameter has to be increased considerably to compensate for internal wall resistance.

One possiblity to minimize the necessary drop would be to install wide and narrow metal duct, but again, when a duct is narrowed down, there is an increase in wall resistance so they may have to be quite wide to compensate.

An alternative would be to consider high pressure ducting. Small diameter round ducts can be used but keep in mind, if you increase pressure and reduce the size, you also increase velocity which can result in an undesireable noise level.

[imeduc]

You dont say the sq ft you have here . But why didnt you just put another unit in and let the old unit as is. Hate to say how many of that high pressure small round duct we have taken out. Even back to the Coleman 3" round.

ED

My mistakes dont define me they inform me.

[Vatmax]

Hi Again!

Thanks for all the input!

The reason for the new furnace is that the old furnace was the original from 1946. So when designing the new addition that totals approx. 1,150 sq. ft. of additional living (heated) space, we decided a new furnace that can handle the entire house would be best. In addition, we wanted to add A/C.

I'm not sure how round or flexible duct will help us. Remember, the ducts have to run perpendicular to the joists. We had the new basement dug extra deep so that we would have a full 8 foot ceiling but we neglected to figure in the duct work that will reduce that height by about 7". My mistake. Now I'm trying to minimize and unsightly ducts that will have to be dry walled around running right through the middle of the room.

My GC says that code prohibits them from running ducts through the engineered trusses. They can run up in-between them, but not through. Since the headers have to run perpendicular, they will have to hang below. We might have found a solution though. The headers measure about 16" x 6". If they can be mounted vertically where the ceiling meets the wall, and run along the wall, we would only have about a 6" or 7" notch to drywall around. That would look much better than a 16" run going across the middle of my ceiling.

Thanks for everyone’s help!

[imeduc]

Most duct work is 8"X---". To make it 6"X it gets to wide. For this duct work and the plumbing pipe's we pour basement walls all 10' now.
For another 1200 sq ft I think Id go with 2 new units there.
ED


My mistakes dont define me they inform me.