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dlr98004

sealing ductwork in 1970s Seattle home

dlr98004
11 years ago

Thanks in advance for all the information in these forums. So helpful! We have an unheated, vented crawl space in our home. About 32 x 24 built in 1976. crawlspace ceiling joists are 4x6 beams, 4 feet on center. crawlspace ceiling is 2x6 tongue-in-groove boards. About 5 feet of headspace to work in. No insulation at all. Ductwork runs through the crawlspace. We plan to seal the ductwork with mastic and then insulate the ducts. We plan to stay in the house for at least 10 more years.

questions:
how should I clean the ductwork prior to installing the mastic?
what brand of mastic can I purchase? hardcast iron grip was mentioned in one post - will a HVAC supplier sell to me? I can probably order online but will take a couple weeks. What about big box mastics?

what type of insulation do you recommend to wrap the duct work? in most places, there is room for a couple inches of batting.

Once the ducts are all sealed and insulated, we will insulate the crawlspace ceiling. Leaning towards 2" of closed foam spray insulation. DIY possible? too messy? (we are very experienced DIYers)

Any other thoughts or suggestions greatly appreciated. Thanks in advance for your thoughts!

Comments (18)

  • david_cary
    11 years ago
    last modified: 9 years ago

    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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

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

  • dlr98004
    Original Author
    11 years ago
    last modified: 9 years ago

    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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • countryboymo
    11 years ago
    last modified: 9 years ago

    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.

  • david_cary
    11 years ago
    last modified: 9 years ago

    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?

  • Elmer J Fudd
    11 years ago
    last modified: 9 years ago

    "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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    do they sell to the public or just contractors?

  • dlr98004
    Original Author
    11 years ago
    last modified: 9 years ago

    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

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • Elmer J Fudd
    11 years ago
    last modified: 9 years ago

    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

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • dlr98004
    Original Author
    11 years ago
    last modified: 9 years ago

    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

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

  • dlr98004
    Original Author
    11 years ago
    last modified: 9 years ago

    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.

  • energy_rater_la
    11 years ago
    last modified: 9 years ago

    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.

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