What is your opinion on foaming ductwork (2") on top of existing insulation?
Originally Posted by energy_rater_La
you won't hire someone to unwrap & insulate and rewrap duct system for price quoted in foxbusiness link.
maybe one or two ducts.
in some climates burying ducts is recommended.
ducts in attic waste more than 15%, but architects, hvac & homeowners
still do it.
believe me..if there was a product that provided R-20 ductwork..
hvac supply would stock it, and some hvac companies would install it.
some homeowners would pay extra cost to have it.
sadly..it just doesn't exist.
think of how big & thick the insulation would be on the ductwork. R-19
is 6"..in attics where space is premium & compressing the insulation
derates it..how is it going to work??
Which makes more sense to you? CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10% ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%
foam, when sprayed is thin, then it expands rapidly.
it doesn't always fill in the cracks where seal is needed.
mastic on the other hand is applied with a brush
which pushes the mastic into the cracks. where the ducts leak.
on the jobs where I've seen foam on ducts some of
the problems were:
that there were areas that the foam did not seal
maybe ductwork was wet, or dirty or mix or temp of foam was wrong.
varying depths of foam, from 1/8" to 3"..and everywhere in between.
if ducts are wet, foam encapsulates moisture.
if attic is insulated with conventional insulation, foam can encapsulate
this insulation next to gaps where supply boxes meet attic floor,
on top of the supply boxes & at return plenums.
foam often has voids, I call them honeycombs, where there are large
bubbles in the foam. these areas de-rate the performance of the insulation.
on most of these foam ductwork homes, the reason I was there was because
of problems created by foam insulating the ducts.
most foam companies may spray foam while on the job to spray something else..
be it attic floor, roof..under house. but just to spray ducts takes a lot of time
the company could make more money on..at another job.
once the truck arrives on the job, the foam has to be heated to the right
temp, set up for install takes time. most companies aren't going to go
through all that for minimal monies when they can invest the same time
on a job to make maximum monies.
over the years I've worked with many foam companies.
online things like 'buttering' the stud bays of walls..(1" inside studs of walls
to air seal and then wall insulated with conventional insulation)
are touted as good installs, and they are. but itrw..or at least here in La.
no company is comming to just air seal. they come to do the full job,
and turn small jobs down.
I saw the study of the foamed ducts in the original thread.
IMO it is another of those things that may be a good idea
but have little real world application. unless foam company
worked with a production builder and could do several
installs within the same area.
if foam was an acceptable sealant for ductwork, it would be
listed as an approved product for this work. it isn't.
there are good reasons for this, other than the problems
I've observed in my inspections.
given the mistakes I've seen in foam install jobs,
I'd not let them near my ducts or equipment.
best of luck.
The cure of the part should not be attempted without the cure of the whole. ~Plato
Just for clarification the study recommended foaming ducts to increase R value/insulation value allowing ducts to be burried in loose fill insulation and prevent condensation in humid environments. . It never recommended foam as a way to seal flex duct which only needs mastic sealing on the ends anyways.
Newstudent, since you did not start this thread, you should not be posting in it. That's according to the AOP rules. I'm not a moderator but am compelled to point this out to you, as your posts in this thread may be deleted.
Electricity makes refrigeration happen.
Refrigeration makes the HVAC psychrometric process happen.
HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.