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Insulation on Supply Ducts

Mule

Platinum Member
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Oct 19, 2009
Messages
1,521
Location
Texas
Okay, help me out here.

The 2006 Energy Code states: "a minimum of R-5 insulation when located in uncoditioned spaces."

Then it goes on to say "When located within a building envelope assembly, the duct or plenum shall be separated from the building exterior or unconditioned or exempt spaces by a minimum of R-8 insulation."

If the ducts are within a building envelope assembly, how is it unconditioned? I thought the building envelope assembly was "within" the insulated areas. I don't find a definition on building envelope.

My mind is getting foggy!!

The main reason I am asking this is that a proposed middle school is specifying R-6 insulation on the supply ducts. For some reason my mind says R-8.

This is the same school with the hypodermic :shock: piping system or whatever that green word is :mrgreen: for saving energy!

503.2.7 Duct and plenum insulation and sealing. All supply and return air ducts and plenums shall be insulated with a minimum of R-5 insulation when located in unconditioned spaces and with a minimum of R-8 insulation when located outside the building. When located within a building envelope

assembly, the duct or plenum shall be separated from the building exterior or unconditioned or exempt spaces by a minimum of R-8 insulation.

Exceptions:

1. When located within equipment.

2. When the design temperature difference between

the interior and exterior of the duct or plenum does

not exceed 15°F (8°C).
 

Builder Bob

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Oct 17, 2009
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Sunny SC - Coastal (not Charleston or Myrtle Beach
Re: Insulation on Supply Ducts

EXception

2. When the design temperature difference between the interior and exterior of the duct or plenum doesnot exceed 15°F (8°C).
you may want to check to see if this is the case in your question......

If it meets this exception, then they can put whatever they want.....I think they are going beyond the energy code if the buildig envelope surrounds the ductwork in question...
 

mueller

Bronze Member
Joined
Oct 17, 2009
Messages
57
Re: Insulation on Supply Ducts

Definition-

BUILDING THERMAL ENVELOPE. The basement walls,

exterior walls, floor, roof, and any other building element that

enclose conditioned space. This boundry also includes the

boundry between conditioned space and any exempt or

unconditioned space.

I have a figure in the energy code study guide that I can't figure out how to post.

It shows HVAC equipment roof mounted, Duct work above roof insulated R8, Suppy ducts

Penetrate roof and enter the unconditioned space between the roof deck and the suspended

cieling and are insulated R5.

IMO

The area between drop cieling and roof deck is unconditioned because there would be no supplies or returns in that area.( duct work running through only). R5 is permitted because the ducts are seperated from the exterior by the roof insulation wich of course must be R8 min.
 

Builder Bob

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Oct 17, 2009
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Location
Sunny SC - Coastal (not Charleston or Myrtle Beach
Re: Insulation on Supply Ducts

Here is the slide represented in the post below---

insulated duct above the ACT but below the building's envelope.

Insulatedduct.jpg
 

Mule

Platinum Member
Joined
Oct 19, 2009
Messages
1,521
Location
Texas
Re: Insulation on Supply Ducts

mueller, you would think that the energy code would have a definition for Building Thermal Envelope. I kind-of figured that was the meaning but I was surprised that there wasn't a definition!

Bionic Bob! Thanks for the information. From the slide shown, this is a picture of supply ducts within the "building envelope", because of the insulation in-between the rafters which only requires R-5 insulation. If there were not any insulation between the rafters, then it would have to have R-8 minimum.......Am I correct on my thinking?

So what I need to do is look at where the architect specifies where the insulation is to be installed. Only problem is..........they didn't include any energy specifications with the submittal. Hard to review something that's not there! That is one of my comments on my review!!

Is there some kind of trade-off for a higher SEER rating on the units like in residential? 14 SEER and you can use R-6 on the ducts instead of R-8?

Thanks
 

Dr. J

Silver Member
Joined
Oct 19, 2009
Messages
367
Location
Colorado Front Range
Re: Insulation on Supply Ducts

No duct insulation required (slide is WRONG - must be the same guy who writes the commentary).

2006 IECC:

CONDITIONED SPACE. An area or room within a building being heated or cooled, containing uninsulated ducts, or with a fixed opening directly into an adjacent conditioned space.
An area or room within a building being heated or cooled,..." This clause is one of three conditions, any one of which define a conditioned space. If the ever so smart authors had not included the comma between "cooled" and "conditioned", then this clause would have meant that a space has to be BOTH within a building AND containing uninsulated ducts. With the comma, it is one of a list of three items connected by the "or" (Someone needs to read Eats, Shoots & Leaves).

"...containing uninsulated ducts,..." - If you insulate the duct, it is an unconditioned space, and the duct is required to be insulated, but if you don't insulate the duct, it is a conditioned space and duct insulation is not required.

"...or with a fixed opening directly into an adjacent conditioned space." - A typical plenum return ceiling has fixed openings directly into an adjacent conditioned space therefore duct insulation is not required. I even can find or make a "fixed opening" (no minimum size indicated - how about the vents in a recessed can light?) in the ceiling for a fully ducted return system so the above ceiling area becomes conditioned and no insulation is required. Note the ceiling opening on the right hand side of the picture in the slide.

Before you say, "Well what prevents you from using your superior knowledge of the english language from saying ducts in a crawlspace or an attic do not need insulation", remember that a condtioned space still needs to be separated from the unconditioned space or the outdoors by the building thermal envelope. So if you do put un-insulated duct in an attic/crawlspace, the attic/crawlspace is now conditioned and needs insulation at the attic walls/roof deck.

The concept that ducts in a typical above ceiling space do not need insulation is also supported in the 2003 IECC and ASHRAE 90.1. The definition of conditioned/unconditioned space is much more straight forward in those documents, but not nearly as much fun to ridicule.
 

JBI

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Oct 17, 2009
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Location
The Empire State
Re: Insulation on Supply Ducts

You guys are confusing me... AND I UNDERSTAND THIS STUFF. :eek:

Mule - Think about an envelope, like you get mail in. It 'envelops' or contains the letter.

The letter is the heated/cooled air, the 'conditioned' air.

The 'envelope' is the buildings' insulation, not the ducts'.

Wholly within the buildings insulated walls, ceiling/roof and floor/basement doesn't require insulation on the duct.

Remember why the duct insulation is there... to optimize the temperature of the air INSIDE the duct. If the duct is wholly within the 'thermal envelope' of the building, we are less concerned with losing heat to the environment (or warming of cooled air in A/C mode).

When the ducts are outside the 'envelope' they are subject to natures fury.
 
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