Ducts in ceilings

[psychoengineer]

I am in the business of designing residential ductwork and am being encouraged to keep ceilings as high and uncluttered as possible. Therefore I try to keep the ducts in the floor trusses whenever possible. My question is, is it practical to design ducts to fit into the rectangular block outs that floor truss manufacturers provide? These floor trusses are usually 19" on center. How can they get their ducts into these spaces?

 

[VinceNY]

Are you talking about the main trunk lines in the basement?

 

[psychoengineer]

Yes. Formally the main trunks were hung from the trusses and then soffits were built to hide them. I would like to get the main trunks into the floor trusses, both on the first and second floors.

 

[VinceNY]

Running in the trusses is going to be difficult for the installer. What about putting the unit in the attic and running the mains in the attic space, then they won't have any problems running the branch lines in oval down the wall cavities.

 

[trashcanman]

Another alternative is to use a split system ductless unit. The duct problems go away.

 

[GMcD]

Trashcanman- OK then where do you get the outdoor air for ventilation with these "ductless systems". In a residential application, if you say opening windows or infiltration, I'll call bad envelope design/energy pig on the Architects.

 

[trashcanman]

I have yet to see an outdoor air connection for a residential home. Maybe they show up in 10000-20000 sq.ft. homes though. In any case, doors and windows will be opened and closed during occupation of the house, right? Have you ever heard of someone suffocating in a house (not counting CO from a furnace)? How would you balance the O/A and R/A, especially if a kitchen exhaust fan, toilet exhaust or clothes dryer comes on?

If you insist, there are O/A connections on some brands, like Daikin. Usually a 4" dia. connection on the fan coil. You can run a 4" dia. flex duct for about 50'.

I don't like floor grilles, as I think of them as dirt collectors, but that is just me.

The point is, the ductless systems will solve your problem. They work, are very quiet and efficient. They have been used all over the world for 20+ years (maybe more).l It is an option

 

[GMcD]

Trashcanman: There are a number of jurisdictions in North America where tight envelopes for homes are mandated, as well as fixed ventilation rates and mandatory fresh air connections. That's why I asked. I agree that the mini-splits are a quick solution for cooling (and in heat-pump configuration for heating), but the fresh air and make-up air issue for them is also something that needs to be considered. If no fixed fresh air connections are used, there is a good possibility that the house can be under negative pressure while range hoods, dryers, and bathroom exhaust fans are on (individually) and uncontrolled infiltration through the envelope in a hot and humid climate or a cold climate is not something you want to do.

 

[psychoengineer]

Ductless systems tend to be expensive, especially in a whole house application. I am trying to stay with a standard furnace and condensing unit, but hide the ductwork within the floor trusses. The 2006 IRC discourages attic distribution due to insulation and leakage issues. I am considering putting in openings in the rim joists to slide the main trunks in from outside. Has anyone ever seen this done before?

 

[ChrisConley]

I'm just going to jump on board with GMcD on the issue of residential ventilation. All new homes in my jurisdiction are currently being built with HRV. However:

Trashcanman- OK then where do you get the outdoor air for ventilation with these "ductless systems". In a residential application,

The advantage remains that you can duct very small ventilation ducts rather than big heat/cool ducts in a ductless system.

I don't disagree that ductless systems (with ventilation ducts) are expensive, but if a designer can't stand the thought of a furred out duct or demands high ceilings without building them higher and still wants air conditioning then....

To answer the OP question, commonly I've seen return air ducts done the way you describe, but never supply ducts.