[dunburn]

I am contemplating adding insulation to my ductwork -- which is in the basement of my 1800 sq ft bungalow. I am talking about insulating the ducts theselves to give them an R-6 or R-4 rating. The ductwork is 80% accessible in an unfinished basement.

If I insulated the ductwork with a product like rfoil (at http://www.tvmi.com/rfoil/), would the cost savings be worth the cost outlay and the effort?

I have already used the metallic-based rfoil tape on the joints of the ducts.

 

[t527ed]

personally i hate to see ductwork insulated in a basement after it has been installed if the house has a/c. always seems to end up full of water from ducts sweating because you cannot get a tight seal in vapor barrier. basement is part of house envelope and any heat it loses is going into house.

 

[mayguy]

For a basement I wouldn't bother.. Unless you have a very cold drafty basment.

You'll need that little warmth on the floor, and also help keep the basement some what warm and keeps the water from freezing up.

 

[36292]

Bubble foil is radiant barrier and needs airspace for the R ratings stated. Read the rfoil site carefully. A better product for ducts in the basement is the 6" and 8" fiberglass/foil sleeves available at your local HD or builder supply store. Nothing fancy, but an honest R6 without any additional airspace.

 

[dec]

I was talking to an inspector today and he claimed that bubble wrap insulations R value is minute almost 0 r value. I know a lot were talking about how much easier it is to install. Guess it wont meet code if you have a code lol

 

[36292]

DEC, thank you. Precisely. Just look at it. Just aluminum foil. Aluminum is a good heat conductor, not insulator. Only good for radiant barrier, as aluminum has very good reflectivity.

 

[dan sw fl]

Requires Insulation, NO ?

I am contemplating adding insulation to my ductwork -- which is in the basement of my 1800 sq ft bungalow.

would the cost savings be worth the cost outlay and the effort?

If the duct does not Sweat, Why insulate?

If the duct does Sweat, use a very thin (<= 3/8") ARMACELL sheet insulation. Hopefully you only need ~ 50 feet.

http://www.armacell.com/www/armacell/armacell.nsf/ansHTMLSeitenLookUp/USA_Frame?OpenDocument

AP/Armaflex Sheet and Roll Insulation is a flexible, elastomeric thermal insulation, black in color. It is furnished with a smooth skin on one side which forms the outer exposed insulation surface. The expanded closed-cell structure of Armaflex makes it an efficient insulation. It is manufactured without the use of CFC's, HCFC's, or HFC's. It is also formaldehyde-free, dust free, low VOCs, fiber free and resists mold and mildew.

AP/Armaflex Sheet is supplied in flat sheets 36" x 48" (.915m x 1.22m), in nominal wall thicknesses of 1/8", 1/4", 3/8", 1/2", 3/4", 1", 1-1/2" and 2" (3, 6, 10, 13, 19, 25, 38 and 50mm).

AP/Armaflex Roll is supplied in 48" wide (1.22m) continuous rolls in nominal wall thicknesses of 3/8", 1/2", 3/4", 1", 1-1/2" and 2" (10, 13, 19, 25, 38 and 50mm). It is also available in 60" (1.53m) in 1" thickness.

 

[36292]

Dan, what is the R value of that 3/8" foam?

 

[dan sw fl]

Tech Info

Dan, what is the R value of that 3/8" foam?

R= 1.4 for 3/8" sheet

Note that one is only concerned with
preventing condensation
with the use of a minimal thickness
in this specific case. The temperature difference for this possible use is < 18'F.

If you wish to use for another applications,
see the companies technical information.

http://www.armacell.com/www/armacell/armacell.nsf/ansHTMLSeitenLookUp/USA-TI_Frame?OpenDocument

[Edited by dan sw fl on 09-16-2005 at 06:46 AM]

 

[dunburn]

Why am I interested in insulating my duct work? Well, I am looking to increase the efficiency of my heating system so that more heat or cold air is pushed up through the registers to where it needs to be.

Ultimately though, I am looking to help save money, but also help the environment - in Canada there is goal to decrease greenhouse gas emissions by one tonne per person, and I want to do what I can to help.

Sub-questions:
1) Insulating duct work is one of the recommendations to help meet part of that challenge. In fact, I have heard that insulating your duct work, even if in a fully accessible basement, is one of the things that can be done that has the highest return on investment re: energy conservation. Any sense if this is true?

2) I have not had a problem with sweating - would insulating the duct work increase the likelihood of sweating or cause otherproblems? I am not sure I understand why this would be the case...

 

[dan sw fl]

$ Return

1) Insulating duct work is one of the recommendations to help meet part of that challenge.

In fact, I have heard that insulating your duct work, even if in a fully accessible basement, is one of the things that can be done that has the highest Return On Investment re: energy conservation.

Any sense if this is true?

Unless the ducts are in the attic or garage,
you are not losing ANY overall heating or cooling.

Wouldn't getting rid of windows be nearly the best R.O.I.?

You can always turn the t-stat down to 58'F in the winter
or cool to 82'F in the summer. It does not take to much investment to adjust the thermostat.

 

[36292]

dan_sw_fl, I think you are missing the point. I work on a lot of houses where the basement is too cold in the summer. Even with all duct leaks sealed and no registers, I routinely see basements at 64-68F when the first floor thermostat is at 73-75F. All of the cooling is from the duct surfaces. These are typically below-ground basements with 2 furnaces. Some of these same houses have second floors that cannot cool properly, because of marginal ductwork, insufficient insulation, undersized AC, etc.
By having the ducts fully insulated, I can bring the basement to comfortable levels AND save energy. By fully insulated I mean round ducts, trunks, plenums, everything accessible. The energy (and cooling capacity) saved by not over-cooling the basement can be used to save money or for deployment somewhere else in the house where it may be needed. As far as investment value vs other insulation, etc. strategies, it depends on the house.

So yes, danburn, what you are contemplating is sound. Make sure to first tape and/or mastic all duct leaks carefully, then insulate with R6 or better. You also mentioned that you used rfoil on the duct joints. Check with your local building official. Around here, the only tapes that meet code for duct joints are the ones with the UL listing printed and visible, such as Polyken 339.

 

[cem-bsee]

since winter is comming soon, insulate the outside wall of the bsmt, at least down to the frost line! Glue Styrofoam to wall -- go down 8+ inches, put a layer horizontal, out 2ft from wall, then backfill.
read info @ BUILDINGSCIENCE.com
& STYROFOAM.com = Dow Chemical

change out bsmt windows to be glass block to cut down infiltration --
but, you need combustion air piped in if you are using an open flame.

 

[dan sw fl]

Location

dan_sw_fl, I think you are missing the point.

I work on a lot of houses where the basement is too cold in the summer. Even with all duct leaks sealed and no registers, I routinely see basements at 64-68F when the first floor thermostat is at 73-75F. All of the cooling is from the duct surfaces.

I see your different perspective.

R value is expressed in units of ft2•h•°F/BTU.
1/2" R value = 1.86

EXAMPLE:
Max Basement Temp = 70'F
Supply Air Temp = 60'F T = 70'- 60' = 10'
Duct Surface Area
100 feet x ( 18" * 2 + 12" * 2) = 500 Sq. Feet

Q= U * A * T = A * T / R
Q = 500 * 10'F / 1.86 = 2,500 BTU/h

I believe that with 1/2" of Armaflex foam insulation on a long duct in the basement that the cooling loss to the basement would be < ~ 1/4 ton (6% loss for a 4-ton unit).

In other words, I guess that a maximum of
1.5'F temperature rise from
the air handler to the diffuser may be a realistic goal.

More later.

 

[dan sw fl]

Location

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