Ductwork Insulation

[laynes69]

I was wondering what the heat loss could be in the ductwork with no insulation. I've considered insulating the main trunk because if runs through an unfinished unheated basement. We have our wood furnace tied into the ductwork, so it's the main heat source for the home. I wasn't sure if there would be a large difference with the ducts insulated. Also what are some of the types. I do know that I need to insulate the duct in the attic because its super cold and that part of the ductwork heats the upstairs. Just wasn't sure what percent of heat loss can occur w/o insulation.

 

[spot]

Heating and cooling an average home usually costs about 50% of your energy bill.
Water heater = 22%
Fridge = 15%
Lights = 13%

The average duct system can lose 10 to 40% through gaps in duct joints and thermal loss through the metal sides of the duct itself.

So insulate those ducts!
You will notice a difference in comfort, and in your bill.
(whether you cut a check to the gas/electric co. or your wood supplier)

You want the heat (and in summer - the A/C) to get where it is supposed to go.
You don't want any of it to "leak" out along the way.

If you had a water pipe that leaked, even only a little, you would fix it, right?

Insulating ductwork is an inexpensive and easy project to do, so go for it.

While we are on the subject:
In the average home...
35% of heat is lost through the gaps around doors and windows.
18% directly through the doors and windows themselves!
(a door or window cannot hold in the heat as well as an insulated wall)
17% through the floor into the unheated basement or crawlspace.
13% through poorly insulated walls.
10% through the ceiling into the attic.

That leaves only 8% to keep you warm!

(Family Handyman magazine - October, 2001, pg.34)
(www.familyhandyman.com)

 

[laynes69]

Well, Wood is free, but comfort is important. I installed new ductwork last year, but never insulated it. Theres no air leaks in the ducts, so maybe insulation is something worth looking into. Thanks.

 

[elkimmeg]

Unless you used duct mastic and sealed every joint and every elbow and every take off, you have leaks. Even insulated ducts not sealed and inadequate insulation looses 35% in transmission losses. Aa huge leak area is at the furnace exchanger connection

The minium insulation value should exceed R 5.0 roughly 1.5" fiberglass. Most around here use 1.75". The bubble wrap, eventhough listed , has been proven to have an r value 1.1 not the 4.2 I think it fair to estimate at least 50% heat/cooling loss in uninsulated ductwork, especially in the attic. The other factor is condensation control. Every leak in that attic produces condensation insulation is an preventive layer reducing condensation, that applies to supplies and returns. There is a lot of things we should be improving, duct sealing and insulation is one..

Btw that tinfoil tape is just about useless for sealing ducts. The Heat effects the adhiesive and it looses that property and the seal last about a day. Use Duct mastic. Since you have a an attic location, that probably means you have ceiling return locations. Just about as useless as tips on a Bull. You want effeciency you need to use a high low return system. As simple as cutting the drywall and using the stud bays and installing dampered grills. Open the lower level for heating close the top and reverse that setup for AC. The lower grill location will remove the cooler bottom air and draw the warmer light air down to replace it. It never happens with ceiling returns.

 

[laynes69]

The house is about 150 years old. The whole upstairs was drywalled about 14 years ago, So removal was out of the issue. My returns are on the base of the wall on the inner walls of bedrooms upstairs. I used the existing heat ducts that were shared between 2 bedrooms and converted those ducts into returns. The supplys were put in the ceiling because I didn't feel like demolision to install ducts. I cleaned all the joints with alcohol and applied the foil tape in layers on each joint, transition and even adj. elbow. Mastic would have been great, and maybe this summer I will redo them, but the tape has held well and I know for sure there are no leaks. Those supplies in the ceiling are on the other end of the room between the windows on the exterior walls. It was my only option, also discussed with the local hvac people here. Like I said, I will most definetly consider insulation because of the long run I have with the trunk. Someday cooling will be added to the home, but then I will have to have a air handler with electric strips installed, or modify the ducts to allow for a larger plenum on the LP furnace to accomodate the heat pump.

 

[elkimmeg]

Laynes69: I commend you for doing the best possible duct installation possible given your existing setup. Yes insulation will reduce heat loss in transmission
due to exposure and also reduce condensation

 

[laynes69]

Thanks, I researched quite a bit online and studied quite a bit on the ductwork. When the hvac came out to look at the furnace, I was offered a job installing ductwork for a local company. The old setup was a joke, all of the return air was pulled from the basement where the dust, mold and moisture was when I purchased the home. Also the woodfurnace was down there. Dad ran it this way for years. The old heating ducts were oversized and on the inner walls instead of the outer walls, so I added heating ducts downstairs between the windows, and put good returns on the inner walls both up and down. I did away with the returns in the basement, because the ducting was drawing combustion air from the wood furnace, not to mention the old ductwork had been in the house for 40+ years. There was over 2 inches of dust settled in the returns, and probably a 1/2 inch in the supplies. It was one hell of a nightmare. All is good now, and with the furnace being installed in series with the woodfurnace, the house heats 10 times easier. Can't have a supply with no return.

 

[begreen]

All I can add after doing a total duct insulation this summer, is it's a day and night difference. Before we had cold air constantly leaking up from the ductwork. No more.

You will be glad you did it, assuming you don't have issues with critters burrowing or stealing the insulation. If you have vermin in the area, address that first, then insulate.

 

[Henz]

what kind of duct insulation is ther out there? I have ductwork that rund through my uninsulated crawlspace but its mostly plastic/flexable stuff. How can I insulate this?? There are spots where it branches off where I can insulate..Its like a big box..How can I insulate that?

 

[elkimmeg]

Not a one sentence answer ant I'm off to bowling tonight I will try to respond when I get back in