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Old 11-28-2012, 10:48 AM   #1
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Insulating duct

Hi All,

In my home we have a heat pump. The air coming out of the furnace is about 95-100F which is correct. By the time the air gets to the furthest vent of the house (bedroom above garage) the temperature can drop to 85F. And it's about 30F outside.

In our unfinished basement we have the furnace and the duct runs the entire length of the house with 2 turns. The main rectangular duct is about 50 feet long.There are various connections from this rectangular duct to 6" round ducts to each area.

I found the following web site that calculates heat loss in duct work
i entered the following data...
starting temp =100F
ambient temp = 70F
Flow rate=500CFM
Length=50 feet
Perimeter of duct = 48 inch
R value of insulation of duct =0


Simply by insulating the ductwork would be a great improvementů

Change R Value to=3 result=97F
R=6 result=98F

So it seems simply by insulating the ductwork within the living space will greatly improve the situation. Even just R3 will have a major impact.

What type of insulation would you recommend? Not too expensive as we have alot of ductwork. And also in Canada, weird as it sounds, choice might be limited.

Styrofoam boards?
Duct wrap?
Do you really think I will see an imporvement? Note the ductwork is inside the heated space. Although there is some in the garage.

Note some rectagular ducts, some round ones...

Thanks in advance,


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Old 11-28-2012, 11:39 AM   #2
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While I am not in canada, I am in phoenix (desert climate). I can tell you that I insulated my attic ductwork and realized a savings of around 25 percent in the hot months. comfort was also greatly improved!!!

I used r13 fiberglass times two wraps (r26??) and a reflective vapor barrier on the outside, after using about a ton of mastic to seal the outside of the ducts. The delta t from the air handler to the furthest register was a drop of about 30 degrees before the wrap. after the wrap (and some flex duct taken out). Now the delta is only 10 degrees on the hotest day on the farthest run (5 ton 2 story house, with all metal ducts.

The cost per foot is a question that I never even considered. I just did it... The labor was not fun, but I did the labor and I know its right.

bottom line,
1. duct seal the outside
2. fiberglass insulation on the outside
1 + 2 = 25 percent savings.



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Old 11-28-2012, 12:11 PM   #3
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Quick FYI we don't have ducts in the attic. I know that space is unconditioned and you will save buckets of $$ if you insulate your ducts in the attic. And be more confartable too

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Old 11-28-2012, 12:21 PM   #4
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Originally Posted by tls1 View Post
The air coming out of the furnace is about 95-100F which is correct.
Where did you take your temp reading? I used a dual probe thermometer and put a probe in the cold air return and in the plenum. The temp of the air at the plenum maxed out at 137 degrees F. If yours is only 95-100 I dont know.

My furnace is a Goodman model GMPN100-4 furnace. (natural gas, single stage, pilotless and an input rating of 100,000 BTU per Hour)
Attached Thumbnails
Insulating duct-100_7622.jpg   Insulating duct-100_7618.jpg   Insulating duct-100_7621.jpg   Insulating duct-100_7623.jpg  

Last edited by hammerlane; 11-28-2012 at 12:25 PM.
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Old 11-28-2012, 12:23 PM   #5
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We use a heat pump when the weather is warm... Warm is defined as warmer than -10C (14F). heat pumps provide approx 100F heat at the plenum. No more. Outside temp hovering around 0C (32F).

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