I thought I'd bring up an important part of system design that seems to get less thought. I will have new metal ducts to go with my new system. For the second floor, I will be bringing the main up from the basement , T off and most likely flexibe to the ceilings. Since this is above my envelope, sealing and insulating is most important.  I saw on tv where they encased the metal in closed cell foam. I was thinking this is a good idea.  How do you guys feel about this? Anybody done this?

Would you insulate the plenum that rises to the attic as it passes the 2 floors?

Code requires insulation of duct in unconditioned spaces.
I am not convinced there is a net benefit to insulating duct in conditioned spaces.
J

Down south a major reason (aside from code) for insulating duct in conditioned spaces is to prevent sweating during cooling season. We are allowed to drop to R4 in conditioned or indirectly conditioned spaces.

While we don't have the humidity of the South, we are not all that far behind. I did talk to a local contractor that does foam and they were not too interested in just the ducts with the setup factor. But if I wanted to do the attic space around the duct, they would be more interested. Adding foam under the trunk down to the sheetrock would insulate and avoid fiberglass compression. But they were thinking open cell. closed cell would be 50% more for the same R value.

My steel pipe (metal) ducts are insulated with R-8 insulation wrap, on both the supply and return sides.

Best regards,

Bill

Closed cell foam is pricier, but offers strength, more R-value per inch and is a vapor barrier

Bill, Nice pic. Why did they not insulate the air handler? Seems that would be a big loss area.
Engineer, I asked about the closed cell and the vapor barrier. The response was that several inches of open cell had a permeability of less than 1. Also easier to remove for any future work.


I am considering buying a do it yourself kit and going to town. Maybe start with a 600 sf kit and do the ducts and area around it. If it goes well, get another and finish it off or pay a contractor to finish the hard part off. I have a 5/12 pitch with 2' eaves and it was hard enough to get my body in there years ago to add insulation perpendicular over the trusses. My soffets are fully ventilated and a full ridge vent on a new metal roof so going unventilated doesn't make sense. I don't plan on using that area for storage

They are sadly mistaken about open cell, to the point that they could be considered negligent in the eyes of the law should your home rot out due to moisture problems. It takes several inches of CLOSED cell foam to reach a perm rating of less than one. Open sell has more than 10x the permeability. I've seen 16 quoted for 3 inches. For example, see:
http://www.envirogreeninsulation.com/open_vs_closed_cell.html

Posted By Volleyball on 09 Jul 2010 09:37 AM
... Why did they not insulate the air handler? Seems that would be a big loss area. ...

I don't know why my contractor didn't insulate the outside of my (WaterFurnace Envision's) cabinet.  Nor do I know if this is common practice.  The subject never came up in our conversations.

I do know that inside of the air handler section of my cabinet, there's about one-half inch of foil faced insulation on all walls and ceiling.  Here's an image where you can see the insulation:




Additionally there's about 1" thickness foil faced insulation on the floor of the air handler box.

The equipment box, underneath the air handler box, also has one-half inch foil faced insulation on of its walls.

It would be an interesting project to see if it would make a material difference if R-8 foil faced insulation was wrapped around the cabinet, a la wrapping an electric hot water heater.

Best regards,

Bill

Cabinet Insulation would help but make troubleshooting and maintenance a huge PITA

It would add to servicing but it is like other things. How hard will remodeling be if your house is all done with closed cell ? If my furnace was in unconditioned space, I'd build a foam box to go around it. You could cut the tape and open it up quickly then reposition and tape or build a permanent "birdhouse" large enough to allow servicing. My current electric water heater is in a kitchen closet with 1" foam built in. I still wrapped it with a blanket so the closet stays at room temp even with the door closed.
I am giving up some desirable space to put my furnace in the basement to keep it in conditioned space and ease servicing. I remember how warm my parents basement was with two furnaces going especially with one being a hot air system which I ended up replacing for them when I was an adult with a warm air system