I know this doesn't answer your question but have you thought of just sealing the crawlspace? Every locale is different but in NC, if I had your issues, I would just seal the crawspace. The ground is warm enough and it would all be so much easier than doing what you are trying.

Some rigid foam on the walls, some thick poly on the floor - overlapped, taped, and run up the walls.

I buy CCWI-181 mastic @ hvac supply.
sets up to harden within 24 hours
and dries to dark gray. for both indoor
and outdoor use.

I used to buy Hardcast Iron Grip...but
at $30+ per gallon..the CCWI-181 is a much
better buy.
Some hardcast paint on mastics don't dry, the stay
semi flexible. it can be really messy to work with
when insulating over it or securing flex outer liners.
I want a solid seal that can
withstand extreme attic temps and still dry farily quickly
enough in cooler crawlspaces.

Now Hardcast makes an excellent mastic tape.
Hardcast brand #1402 mastic tape.
I pay about $25 a roll from hvac supply for this
tape. strong, thick mastic unlike box store mastic
tapes. over the years I've tried just about all
brands. but Hardcast 1402 is THE best.

knowing what type of ductwork you have will
help to advise you.
hard pipe ducting or flex duct?
is supply plenum, heating system & return
plenum (s) located in crawlspace?
supply box enter house through the floors?
return(s) in floor?

I've done a lot of ductwork over the years.
I've learned what works & lasts as opposed to
what doesn't work & what doesn't last. like
duct tapes & foil tapes.
I've also learned by testing ductwork where
and how to best seal it.

if you'll describe your duct & system set up
including returns I'll do my best to walk you
through whatever you want to seal.

if you post pictures..that will help.

your general location would be helpful also.

I think you are on the right track with leaving
the crawlspace open, sealing & insulating duct
and putting 3" closed cell foam on undersides of
floors.
my ducts are in the conditioned/living space
open crawlspace & 3" of closed cell under floors
is the next step for me. I've done a lot of research
as per my job.

as long as the crawlspace doesn't have low spots
to hold water & there are no issues with it..why
change the dynamics by making it unvented.
just opens up an whole new world of issues to
be dealt with.

I also do a lot of diy..and effieicncy work
for others. I'd never attempt to spray foam.
much easier to hire it out.

we did all the work for ducts in fur downs
inside the house, installed heating system inside
and heatpump outside. (yes, I hav epa license!)
my house is lower to the ground than yours..
I'd love to have that much room to work
under my house!

I do work with a lot of foam companies so I've
seen & tested the work..and know who to hire
and who to never hire.

know that prior to foam being installed you'll need
to close big openings. the opening under the tub
is one place. if gaps are over 2" wide..some
filler should be in place prior to foam
install. foam board nailed in place..metal flashing
screwed in place...etc.

also youtube videos make it look easy..because
they either have a lot of experience or an above
average situation to work in.

if you decide to diy..try a small area first
before investing a lot of money. if it is something
you can do well..then order more. if not
you've not invested too much $$ & can hire it out.

also keep in mind that 2" isn't much. I'd up it
to 3" and 3" everywhere. not just 'average' fill.
average fill means that some areas will have less
& others more, so that it averages out to x".
what you want is minimum of x". more is ok..less
isn't ok.

depending upon where you live I might be
able to recommend hvac supply where you
can get your materials. box stores dont
have the quality of product you get from
supply houses.
there will be tools you'll need depending upon
duct type, if you have hard pipe ducting you'll
need to buy duct wrap. so establishing a
relationship with your local hvac supply
house is worthwhile. unless you have a friend
in hvac who can help you out...

best of luck.

oops ...missed the Seattle location in title of thread..

Hi,

Thanks for the replies. We are in Seattle and the local experts do not recommend sealing the crawl space for anyone that lives west of the Cascade mountains. Just too much moisture.

The pipe is galvanized hard duct work. A 12' 12" round supply comes directly from the down draft furnace into the crawl space. 4 6" lines each about 10' take off the main supply. One comes from directly from the supply the other three come from a box at the end of the main supply. the main supply then head up into the next level to supply for the second story.

Returns? Funny, there are no returns in the crawl space. The open floor plan and the moderate temperatures allowed the installers to put returns in one place near the furnace.

We live in Bellevue which is east of Seattle. We have been searching for HVAC supplier that would sell to us (we are not contractors). No luck so far. If you have a recommendation that would be fantastic. Need the sealant and recommendation for the insulation. Had rats in the past so all the old insulation had to come out. R8 is code but R11 seems to be recommended.

Thanks for your help.

we may have to work out the details of materials
by email. you can contact me by clicking my
user name I think.

ok so you have hard pipe ducting. and returns are
inside the conditioned space. good. we'll deal with
the returns later.
this post will be about sealing
the ducts you have in crawlspace.

the supply ducts start at the supply duct and
terminate at the supply box. the other side
of the supply box is inside the house. sealing
of the supply box to supply grill will also
be another thread, that I'll attach a pic
that shows final install of seal for that area.

I'm not 100% sure how supply goes from inside
house into crawlspace. maybe you can attach
a pic of that.

tools you'll need to seal wrap & strap ducts are:
razor knife
cordless drill & 1/4" self tapping sheet metal screws.
duct strapping. I usually use metal plumber strapping,
but you can also use 3" duct strapping.
straight edge 4' long. I use a 4' T so that I
can keep my duct wrap cuts straight & square to edges
of wrap.
duct stapler & duct staples this stapler flares
the staples out, rather than in, so that the
duct wrap is secure.
then this seam is covered with fsk (foil scrim kraft)
tape.

when you cut the duct wrap..it has to wrap around the
duct and overlap. @ the overlap you remove 2" of
the insulation so that the staples go through the lap
edge of the duct wrap and into the fsk (foil scrim kraft)
facing of the duct wrap. you make a double row of staples..
you don't want the duct wrap to come lose..and gravity
is your enemy. lots of staples, fsk tape. then I put a row
of staples on both sides of the fsk tape.

on a moderate temp day, you'll remove old duct wrap.
at this time, inspect all connections 90degree ells
where they connect to straight runs. these need to have
at least 3 screws evenly spaced around where these
two parts of the duct run connect.
then you'll mastic seal.
paint on mastic with small brush. make mastic
'nickle thick'. use the brush to push the mastic
into each joint/seam.
you may have to clean as you go.
depending on how much insulation sticks to duct
or where it is dirty & you need to seal.

round pipe duct has a long seam where the sheet
metal joins. this also needs to be mastic sealed.
the join of the 90 to the section of duct, and each
joint of the 90.

as you unwrap, you'll see what I refer to above.

work from each supply where it enters the house
back to the supply.
where the duct attaches to the supply box..
clean, screw, mastic seal.
screw the strapping directly to the sheet metal duct.
if you use metal strap..it has predrilled holes.
then pull the strap tight and screw it to the
nearest joist.
if you use duct strap, before you screw it to the
duct..fold it over 2" so that you screw through
2 layers of strap. do the same at floor joist.
support often & well to keep gravity from pulling
ducts down over time.

use mastic tape to seal around the opening
into the house to the supply box.
you'll address this again from inside the house.
if the box is uninsulated, use the ductwrap to
insulate the box.

do all the mastic sealing on one day.
let sit until next day and run heating system
as needed. it will help to dry the mastic.
you want the mastic dry before installing
duct wrap.

always always keep in mind, that if you compress
the duct wrap..it loses its R-value.
this is why you cut the insulation off the edge that
overlaps when stapling wrap on ducts.

also duct wrap has different ends on the roll of
wrap. one end of the wrap has fiberglass all the
way to the end of the fsk paper, lets call that the
butt end. the other end
has about 1" of insulation missing, this is the end
that overlaps the butt end of the other section.
when installing the wrap, you want to meet the
butt end of the wrap with the overlap end.
butt the second section with the overlap to the
first section with the butt end. you want the
two section's insulation to touch. if they don't
it will condensate. so butt the insulation.
fold the fsk lip over the first duct wrap section.
use stapler to hold pieces together, then fsk tape
and staple again.

repeat this process until you have wrapped all
the supply ducts.

by the time you've worked with the wrap
you'll have learned a bit about how best to
cover 90 degree bends (I cut a triangle piece,
with fsk lip, staple tape and staple the tape)
supply boxes & different things you come across.
then the duct that supplies all the runs...ahhh.
almost home!

you with me so far?
and now you get some understanding as to why
people like me charge so much? but if you
get it right the first time. you are golden.

do you have aninmals that get into the crawlspace?
we do. this is why you see lattice around the houses.
the folks who know...put a hardware cloth behind the
lattice and rat poisons in the crawlspace.
others put the hardware cloth or chicken wire
on top of the duct wrap. that is a pita.
hardware cloth's cut edges will rip you up.
but mice can't get in. chicken wire is easier
to work with..but has big enough holes that
mice can chew into the wrap.
plus..you have to work each duct again to
install wire/cloth. I perfer the
lattice & hardware cloth. the poison keeps
mice/rats dead.

so, do you think this is a diy you & your SO/DH
can do together?
My SO & I work together. he cuts...I install.
we each have cordless drills and duct staplers.
then I cut..he installs. sometimes we pre-cut
for ducts the same size & work on our own areas.
you'll figure out a rythm that works after
a couple of hours.

should I continue..or do you think this
is beyond your scope??

detail of how to wide to cut duct wrap I'll
have to check out..I know I have a guide somewhere.

best of luck.

It will make a very noticeable difference in $$ saved and comfort level. It might be a lot of work but it will be worthwhile. Sealing the crawlspace does not compare to sealing the ductwork in any climate.

Ok - so maybe in Seattle it is too wet to seal the crawlspace, a sealed crawlspace in my climate is 60 degrees all the time - that helps in the summer and hurts very little in the winter. Now sealing is always a good idea but insulating against 60 degrees is not particularly cost effective in a mixed climate.

Sealing crawlspaces around here was not recommended for many years because of moisture concerns. Science caught up with conventional wisdom and now sealing is recommended. Obviously it still may not be true in Seattle area but a truly sealed crawlspace is as dry as a basement - do they have basements there?

"We have been searching for HVAC supplier that would sell to us (we are not contractors). No luck so far. "

Have you tried Ferguson's HVAC supply operation? They should be up your way, they seem to be everywhere.

do they sell to the public or just contractors?

Hi energy_rater_la, Thanks for the detailed response. We are with you and willing. The duct work has been stripped of the old insulation and cleaned. Screws were added as needed to all joints.

We were able to buy from a local HVAC supplier named East Side Heating and Air conditioning. The carry Ductmate sealant. It will be raining today (surprise!) so DH will be in the crawl space applying the sealer.

Next will be insulation. Should we start a new thread?

We have not purchased the insulation yet. Plan is 3" R8 foil faced but the local HVAC supply says that un-faced 2" 1 foot or 2 foot wide wrap is used most often. This is the stuff you wrap around the duct in a spiral. The old insulation was this type. What do you think?

Will purchase insulation today or tomorrow in the next day or so.

Thanks

nah..lets stay on the same thread.

I wouldn't put R-6 unfaced ductwrap.
without a vapor barrier.
the vb is to keep the insulation clean
& dry. wet insulation loses it's R-value.

hold out for the 4' wide R-8 usually 50' long.
(R-4 is 4x100'. R-6 is 4x75'. R-8 is 4x50')
keeping it all the same shipping rate.

don't buy the unfaced. even if they have to order
the R-8 faced wrap...its worth the wait. and if
you have unopened roll they should take it back.

on the bag the wrap comes in is the lenghts you cut
for what size ducts. usually adding 4-6" including
the lap (without insulation to fasten) will work.
but check the bag, incase I don't find my table for
that.

materials you need from supply house are:
wrap
fsk tape (foil scrim kraft)
to seal stapled seams
duct stapler (a must have)
duct staples
duct strap & sheet metal screws
paint mastic & brushes
mastic tape.

keep the length of each install the width
of the roll 4'. that the ends butt and overlap
is very important.

I usually have a roll of duct tape handy
(don't tell!) when first putting the wrap on
the duct, you'll need something to hold it in place.
use 5-6" lengths of duct tape to tape start end
of wrap to duct, then wrap the rest of the wrap
around the duct, overlap..staple, fsk tape, staple
tape. staple overlap over butt end..staple, fsk
tape, staple fsk tape. move to next 4" section.

once you've worked you way back to main supply
(where all ducts are taken off)
add screws to make sure all is attached well.
keep strapping to sheet metal you'll cut the
wrap to go around this as you wrap.

the take offs on the supply is where I find the
mastic tape to be most useful. sticks well to
clean dry surfaces, and once pressed into place
will last as long as paint mastic. that it makes
sheetmetal to wood, paper, foam sheathing..and many
materials makes it worth the cost. sometimes
ease of install is what you need, and Hardcast #1402
Mastic Tape is the best product.

cut your wrap to lenghts needed. you'll
cut out for ducts once wrap is in place before
securing.
make sure that wrap is cut to fit tight to
the duct take off. the wrap on the duct itself
should be in contact with main supply duct
and wrap for main supply goes over the supply
duct wrap. staple & mastic seal.

where the supply duct meets the equipment..this should
be mastic sealed as well. then use the mastic tape
to seal both supply & return ducts (if this applies).

two things...
you may hesitate at forking out $50 for a duct
stapler..but the wrap will NOT stay in place
long term without it.
also strapping ducts is very important.
you want this job to last 30+ years,
gravity is the enemy.

the mastic you bought dries fairly quickly?
run the heat..it will help it.

any questions?
and btw...if you can learn to do this correctly
do a job for someone else..pay for all your
materials (the duct stapler) & make a few bucks.
I usually charge $2k for 9 supply ducts
supply plenum & return.

let me know when you are ready for the sealing
of the supply box from inside the house.

if y'all have questions..just post.

best of luck.

fyi...I've had to send my SO to some supply
houses in the past.
now I only deal with one companie's supply house.
in the past, the other supply house would try to
tell me what I needed, rather than just sell
me what I wanted. then they'd overcharge me.

so I moved all my business to another company.

don't let them substitute materials.
don't let them tell you how to do the job.

you know its your house, your job and
that you are willing to put in the time effort
and $$ to get it right.
so stick to your list of specific materials.

Re Ferguson, energy said:
"do they sell to the public or just contractors?"

Don't know what their policy is, but they sold me a roll of Hardcast 1402 with no questions asked.

See new post on this topic

cool beans. so now you know where to
go for the Hardcast 1402, just in case
your place doesn't stock it.

don't buy the black backed tape
with blue writing, red writing with
gray mastic.

Hi, This dianelouise's DH. She thought it would be more efficient for me to type the rest of the thread. Thanks for all the help so far. We are too far into this to turn back now. The ducts are sealed. It went well, I think. Its my first time so of course I think it looks perfect :-) There are a few things to discuss but first I need to order the foil faced insulation. I have 55' of 6" and about 20' of 12" duct work. I am using the following formula for the length of each wrap.

Wrap length = 3.14 * (D +( 2*2.5)) + 2 where D is either 6 or 12 and the 2.5 is the compressed thickness of the 3" insulation. I added this twice as the diameter of the finished/insulated duct. The 2" is for the overlap. For the 6" that would be 36.5" and for the 12" it would be 55.5" for each wrap. I used 2.5" compressed based on what I read on a spec sheet. Not sure what brand my local HVAC guy carries. Do you have a recommendation on the wrap or an online source?

I have approximately 55' of 6" and 20' of 12". This results in 66' x 4' of insulation. Does this seem right?

Thanks for the rest of the supplies needed and the detailed instructions. Seems pretty doable. Now to price it all out. Will do that this morning. I have a pretty low price bid from a local installer. That with a 50% rebate from the power company and it may be hard to refuse. Will let you know.

Thanks,
Paul

this is really good info:
http://www.owenscorning.com/comminsul/documents/FiberglasAll-ServiceDuct.pdf

you'll see that page 3 has a guide for cutting
wrap for round/oval ducts.
for 3" wrap you add perimeter plus 17"

with 66' needed, you'll need two rolls
as it comes in 50' rolls. but in the
long run, while you'll have some excess,
you'll also have waste.
better too much, than too little is
my pov. stopping mid job to make material run
upsets me!

this isn't a low bid job. as you've seen
you spend time on details. if you hire it
out..make sure that duct staples are used
as described above, fsk tape is used as above
and straps are screwed to bare metal with wrap
cut & sealed around them.
it would be a shame for the wrap to not be
done as we've discussed and it to fail
in short length of time.

best of luck.

Thanks,

I get it. will make sure I understand what I am getting. Since I have cleaned and sealed the only thing left is the insulation. I am having trouble finding someone to sell me the foil backed. The supplier I used for the mastic wanted $255 for a roll. Basically, he did not want to sell it to me. He gave me a lead to someone who also did not stock the foil faced and sent me to local distributor. Have not called them yet. Found stapler for $40 on Amazon.

I will need luck by the sound of it.
Thanks again.

it may be lucky that you finish the install.
its hard to believe that ductwrap doesn't
have foil faced vapor barrier!
is that because y'all usually have ducts
in basements??
does supply house has fsk tape? mastic tape?

I just got off the phone with my supply house.
they are used to 'unusual' questions from me.
LOL! she said the same thing at the $255 price
as I did.
but even if we were to get it here & ship it
there..the cost will be high.
I thought maybe shipping it freight line
would be cheaper..but she told me that isn't
so.
so...online?
let's look for a company near you that will
sell to you & ship. or close enough to you
for you to pick up.

the brand I use is John Mansfield. my
discounted price for R-8 is $115 that includes
tax. so about $102 per roll. taking that
brand & wholesale price, use that as the
perimeters of your search.

I'll go ask the pro's at hvac-talk about
a source for R-8 foil faced duct wrap
in Seattle. will post back with that info
if it is in open part of the forum.