A protective cover with a vapor barrier such as an aluminum foil, referred to as FKS, should be included in insulation specifications. Care must be exercised to protect exterior insulation integrity where insulation comes in contact with hangers, supports, and other structural members. Interior duct insulation lining should not be used in laboratory or cleanroom applications because the insulation tends to entrain microscopic particles into the airflow.
Special consideration must be given to ducts exposed to weather. Lagging materials or heavy metal covers over the insulation are commonly used to protect ductwork. And why. Please advise thank you much. I own a built home and an attic furnace.
I need a price to reinsulate the attic ducts. Question, should they have insulated wrapped on both the plenum and the cold air return for each and does it really work. What kind of insulation wrap would you suggest. I have lived with it this way for 15 years not really knowIng about this issue.
Is it appropriate for a consultant to check Insulation of duct by cutting duct wrap 1 ft square. After removing a piece of drywall in my laundry room, I discovered that the previous homeowner had installed fiberglass installation underneath a heat vent duct? He installed with the paper side touching the metal duct. Is this dangerous? Is this safe? Hi, Kay! What a great question!
I have a single level home with big open attic it has blown insulation and very narrow crawl space but my furnace electric has the single return air duct running about 4 feet from furnace it is in lowered ceiling from bathroom to kitchen ,, my question is can I use a flexible hvac pipe duct an d run a network to living room and two bedrooms the way it is now is very in sufficient, furnace runs almost constantly in cold months , I would appreciate your professional opinion and tips what to do thanks.
Hi, Bill, Great question! I live on a 3rd floor condo with forced air heating. I have accordion style vents in the attic. Would insulating them help the situation? Furnace and ac units are brand new and appropriate for the unit size.
Image Credit: jrodmanjr. Bradford White Partner Information. Homeowners: Commercial Home Builders New Construction. The following information applies to combined heating and cooling ducts in zone 4 areas: R-value of R-6 is required for exterior ductwork or ducts installed in a ventilated attic or an unvented attic above a vented ceiling. R-value of 3. There are no R-value requirements for ductwork installed in an indirectly conditioned space.
Anything we should do to avoid condensation, or is it a non-issue since they are above the fluffy stuff? If there were a possibility of condensation, it would matter but I think the chances of that are low with an ERV. The supply duct brings outdoor air into the house. The outdoor air is cold. The air in a vented attic is cold. Pretty much no delta-T there. There can be a lot of temperature stratification in a hot attic, with the highest temperatures near the ridge.
Great to hear. That is what I Great to hear. That is what I was hoping. I appreciate your quick response. Can you give me your opinion on this insulation job? JC, I think the duct insulation may be the least of the problems in that townhouse.
The air flow is probably pretty bad and once the sheetrock goes up, those ducts are there for decades. Thanks for taking a look. Seeing that type of work is a constant disappointment but I put much of the blame on the developer. This scenario can be avoided in design i. That said, every metal supply-side component should be insulated if system is located in an encapsulated attic or crawl. I meant to mention the risk of condensation but I think that slipped my mind before I finished, so thanks for bringing that up.
I did discuss the issue of condensation on uninsulated intake ducts for ventilation systems in my article on cold weather ventilation problems last month. I believe our Florida code I believe our Florida code required insulation for ductwork within conditioned space is R4. Curt, good for Florida for Curt, good for Florida for requiring insulation! I recall a conversation with a building code official in North Carolina probably 10 years ago.
He acknowledged neither the I-code or NC code address this issue, but their inspectors are supposed to make it clear to HVAC contractors that if their ducts sweat, they own it. BTW, I think R4 is more than adequate, even in severe conditions.
Assuming worst-case temperature gradients, the surface temperature should remain within 5F of ambient. Or perhaps if two flex ducts were mashed tight together. There are multiple requirements for insulation when it is used, but only that one for when insulation is actually required. There is another issue that has been slow coming to the surface. That is the surface area of the ducts. The other way is to minimize the area of the ducts.
Than means smaller AC, furnace of Heat Pump, centrally located air handler and short ducts to the inside wall of each conditioned room.
Certainly no longer than to the center of the room. One additional advantage is shorter ducts present less resistance to air flow. One of my biggest problems with Manual D is that it ignores the surface area and just calculates sizes for the stupid design you give it. I agree with John, and will I agree with John, and will add one more option to reduce duct area.
Instead of putting in one large system, put in two smaller ones. Not only will this allow shorter and smaller ducts, but it will give better zone control. Manufacturers tend to optimize their designs for equipment in the 3-ton range. The largest systems 5-ton are far from optimal because of size constraints in the field.
So there are other advantages to using two 2. Yes, it will probably cost more, but you get what you pay for. Thank you for pointing that out.
What are you thoughts on encapsulating ducts wrapped in R8 in an unconditioned attic with spray foam as shown in this US Department of Energy link? Is this something worth doing as a DIY in lieu burying the ducts in insulation? Current my ducts are suspended about 2 feet above the current blown in insulation, and I am in the Pacific Northwest zone 4 in the Marine Zone.
Adam, I like the idea of buried encapsulated ducts or even just ducts encapsulated with closed-cell spray foam. Until recently I thought it would be a great way to go.
That problem is noise. What this person told me is that the thermal expansion and contraction of metal ducts encapsulated in closed cell spray foam creates a banging noise when the system comes on after having been off for a while. Thanks, I was considering the Thanks, I was considering the use of closed-cell foam for a poorly ventilated very hot attic in Eastern Tennessee after reading the problems of condensation. My guess: advantages are that closed cell should not allow condensation to be trapped within it and it has an excellent R-value per inch.
The Disadvantage is that this can get expensive for large areas of duct surface. Another advantage is that, depending on access to the space and spraying skills, this can be much easier to install. Obviously you must be able to get a foam tank or long hose within range of the application.
The foam I am familiar with is a two-part that mixes at the nozzle and that starts the foaming reaction as it sprays out. Another advantage is a high R-value per weight. Foam has a higher R-v than fiberglass due to the closed-cell structure. And that makes it better at resisting condensation.
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