Ductwork insulation on inside or outside
| Posted in Energy, Heating & Insulation on
I’m used to seeing the blanket insulation wrapped around rigid ductwork. We’re building a house now where the HVAC contractor wants to use insulation on the inside of the rigid supply ducts. It is fiberglass that is coated to prevent fibers from floating away and then ‘glued’ to the inside of the ducts prior to installation. I know these are to code but I’m wondering whether I should be concerned about health issues or quality issues with this approach?
Any thoughts would be appreciated.
-Jonathan
Replies
Mojo-
What's your gut instinct tell you?
"Live Free,
not Die"
I seen our heating guys use a product that resembles the old black celotex, that they fasten to the inside of the rectangular duct halves, before snapping them together.
I also questioned the effectiveness, but they say they have excellent results.
I am NOT an HVAC guy, nor have I researched the product, so my advice is only worth what you paid for it ;)
mike
One school of thought says that inside is better, it's between the conditioned air and the non-conditioned, and "protected" (a bit) buy the actual ductwork.
Another school of thought is that the not-smooth surface is a have for dust, and what not. The ashrae types will also grumble about the roughness increasing the "K" value, and decreasing air flow (by some tiny, if real, amount).
All of which can be mooted by running all ducts in conditioned spaces, a la per Building Sciences.
The interior lining is acoustic lining...while it does have insulating qualities,it's main purpose is to keep fan/air noise down...this lining is usually specified for the first ten feet of run from the unit...
The ductwork should be lined and wrapped on the exterior with a duct wrap (fiberglass insulation adhered to a foil wrapping)...
Thermal insulation=exterior .
Sound insulation= internal.
Have them seal the ducts with Al tape or mastic, then wrap them with insulation on the outside of the ducting.
For your standard ducting, nothing on the inside but shiney metal.
Folks who are medically hypersensitive to airborne nuisance factors would have a cow with the internal insulation you mention. Generates particulates and fosters spread of mildew and mold spores. The less sensitive of us would probably benefit from shiny interiors also.
The product is called ductliner. It is very common and prevalent in all but the cheapest commercial jobs. It is not typically glued, but is rather attached to the duct with special fasteners that resemble brads with large flat heads and are "spot welded" to the duct. It is well suited for the application and an excellent way to inslulate ducts. It's primary use is to insulate the ductwork to prevent it from sweating. Usually this is done above dropped ceilings so there is no inadvertant staining of the tiles. An additional benefit is that is does provide sound deadening where duct wrap will provide no quiting benefits of any consequence. You should only be concerned with health issues if you plan to fill it with dust and debris during construction, run your system with a very cheap (or no) filter and never control the humidity in the space. Modern materials for this product actually have antimicrobial components added that make it very unlikely that heath issues would arise from it proper use.
The only negatives that I know of for this product is that is is more expensive and therefore very uncommon in residential applications and appearantly very misunderstood (as evidenced by the useless information that was posted here previously), it will tend to accumulate dust in a poorly maintaned application and there are some very cheap knock-offs of the good products to be avoided. Also, no practical way to be applied to round duct.
Thank you all for the feedback. We are going with the Ductliner and if we feel compelled, we'll wrap with insullating blankets later. They are using a John's Manville product (I'm getting the specifics today) which from my research seems to be good.
Thanks again.
JM is a very reputable manufacturer of this product. You should have no problems.
Tim