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Biggest air leaks in a home

11 years ago

I'm attaching a pie chart of the biggest air leaks in a home. I was surprised the fireplace is that high up there close to ducts.

The fireplace is probably easier to tackle since it's one area that can leak 14% on average. I just closed the flue and sealed around the aluminum frame glass fireplace doors.

I'm going over the list, but my biggest problem is going to be the floor and plumbing penetrations. Walls have new R-15 loose insulation and ceiling has R-25 insulation.

The doors and windows are next on my list. Even though I have double pane windows, they are 20 years old and I feel a draft around some windows especially on the side track where my windows go up/down to open/close. This is disappointing to find a draft on my double pane windows.

Comments (18)

  • 11 years ago
    last modified: 9 years ago

    even on new windows you'll find a draft in
    the tracks.
    tuck a piece of backer rod in the
    track over the top of the bottom section.
    caulk window frame to wooden framing.
    then caulk apron to sill and window
    frame to walls. caulk all joints in wood trim.
    that will stop leakage.

    rather than investing in new windows..which
    have a 30 year payback, take some
    of that window money & have a blower door
    test done on the house, and a duct leakage
    test for duct work. then get out the caulk gun
    and the first case of caulk

    with the testing, the you'll know what leaks and what is
    worth while to air seal.

    charts like these are misleading.
    truth be told, ceilings are very leaky.
    recessed lights are the biggest culprits,
    with holes cut for hvac supplies running neck
    & neck with can lights. both are dependent upon
    how many can lights & how many supply drops.
    this leakage area is more significant because it is
    directly connected to the attic. extreme temps are
    high up. more moderate temps are lower down.

    one recessed light that is IC rated and not ICAT de rates
    the value of the insulation surrounding it to zero for
    a 1 sq ft area around the light. different methods for
    sealing an Insulation Contact recessed light to
    air tight can be used.

    separating windows & doors from wall area leakage
    and giving them their own leakage rate is also misleading.
    a closer representation would be 32% for ceilings,
    10% for floors and 10% for walls including outlets.
    homeowners focus on window & door leakage too much.
    but it is because this is the leakage area they feel when
    the wind blows against the door or window.
    no one hangs around the bath vent fan, ceiling moldings
    or supply grills.

    this is why we test the houses. to create a situation where
    there is an equal pressure on all sides of the house at one time.

    this quickly shows you that the 1/2" gap behind the
    crown molding in all rooms is larger...and more costly than the
    minimal leakage of windows & doors.
    not to say that replacing weatherstripping of doors isn't
    important..or that caulking window frames isn't a savings
    but it shows lesser important areas vs most important leakage.
    pulling in 200 cubic feet per minute (cfm) of air from attic
    per room is huge compared to 50 cfm at door. especially
    in summer when it is 90 degrees outside and 130 degrees
    in the attic.

    charts like these do one very important thing...they get the homeowner
    to thinking about weatherize their home. taking it beyond
    5% savings to 30+% is what diagnostic blower door testing
    can show.

    note: prior to adding insulation..air sealing ALWAYS
    comes first. otherwise you are just filtering
    the air leakage through the insulation.
    unless insulation is foam.
    if you've already insulated the attic, you don't want
    to compress the insulation or step through the ceiling.
    so you do the air sealing from inside the living space.

    I would never compare sealing fireplace the same
    as sealing ducts. for one thing...fireplace leakge
    is passive, while duct leakage is mechanically driven.
    with duct/return leakage you losing air you pay
    to heat and cool. these two different types
    of air leakage have different costs.

    you can do a LOT with caulk, backer rods, mastic tape
    & time to diy.

    best of luck.

  • 11 years ago
    last modified: 9 years ago

    you'll really like this blog.
    I'm including just one of 48 articles
    on air sealing. Alison Bailes says things
    much better than I.
    this is a great source of info for
    air sealing, insulation & all aspects
    of building science.

    click on lists of articles to right of screen
    for articles you want to read.
    and the comments!

  • 11 years ago
    last modified: 9 years ago


    Thanks for the practical info and happy new year to you.

    I was trying to use the chart to prioritize fixing air leaks, but I see that ceilings are super important.

    I did caulk all my crown mouldings when they were installed throughout house and I see no gaps up in the ceiling. I'll have to check my 9 recessed lights to see which cans I have.

    I've replaced all my recessed lights with cfl bulbs, so can I cover cans with insulation even if not icat? I'm even thinking of getting led bulbs for all recessed lights.

    My two bathroom fans have a backdraft damper, but I have to check cans for air leaks. Im going to do this for new years.

    My stove fan goes through microwave. I did read article that spray foam in a can is a great way to seal gaps around vents for stove and bathroom fans.

  • 11 years ago
    last modified: 9 years ago

    This pie chart does not make a lot of sense to me. In my opinion the biggest source of air leaks in a home are the windows and doors. Make them air tight and you will make a big impact on energy loss.

  • 11 years ago
    last modified: 9 years ago

    The chart says nothing about the actual leaks in any particular house.

    It is only useful as a sort of checklist when trying to seal leaks.

  • 11 years ago
    last modified: 9 years ago

    can I cover cans with insulation even if not icat?
    if they are Insulation Contact (IC)
    take the bulb out and read all the small print
    on the inside of the recessed light.

    mike home
    people think that doors and windows are biggest leaks.
    because they feel the leakage comming in.
    in reality there are many leakage sites that
    are a bigger priority.
    windows present a two fold issue.
    one is leakage
    the other is thermodynamics
    heat goes to cold.
    your warm body by a cold window
    and cold window robs your warm
    body of heat. just the opposite
    in summer.

    the whole replacement windows savings
    of 30-40-50% is sales hype.
    metal window frames transfer heat/cold
    more than frames that are poor conductors.
    like wood, vinyl etc. now a metal exterior
    with wood interior performs well..but it
    is because wood doesn't conduct heat/cold well.

    think about cooking. leave a metal spoon in
    a pot on the gets hot. leave a wooden
    spoon in the pot on the doesn't get hot.

    then the glass of the window.
    single glass has been replaced with IGU insulated
    glass units. that step is a good one, but these
    windows will still condensate. but add a inert
    gas to stop convective currents..another good
    step. adding the Low-E reflects heat out in
    hot climates & heat back in for cold climates.

    these low e, argon glass units in a thermally
    non conductive frame..outside temps don't rob
    your body of heat..or attract the cold.

    people believe that adding a storm window
    does more than seal air leakage. that somehow installing
    a second window 2"+ from original window improves
    window performance. only in stopping infiltration does
    this help. the distance between the two panes of glass
    is too far. within this air space the air sets up
    convective currents. this is not air at rest like in
    a true IGU. the distance between panes of glass
    in an IGU is the maximum before convective currents

    you feel the windows & door issues because
    you live in the areas where they are installed.
    if you lived near the ceiling with recessed lights
    & all the holes we put in'd feel
    those leaks.

    using blower door testing shows the leakage sites.
    better to have leakage from low on the wall than
    at ceiling. attic temps are more extreme than outdoor

    take a look at the following article, then
    click on right side of the screen for info on
    air leakage, insulation etc.

    best of luck.

  • 11 years ago
    last modified: 9 years ago

    I agree air can enter and leave through any opening in the house and sealing all of them is a good idea. The stopping of air infiltration though exterior doors and windows should have the highest priority. If you add up all the gaps of the windows and doors it adds up to the biggest hole. Then add the fact that you have a strong winds pushing cold air through this big hole. The air flow is much greater than any other infiltration in the house.

  • 11 years ago
    last modified: 9 years ago

    Mike, that simply isn't true.

    did you look at the article I linked?

    "Rule #1: Seal the big holes first
    To make a big difference in a hurry, find the big holes. Hint: it's not the windows and doors. Mostly they're in ceilings below unconditioned attics and floors over unconditioned crawl spaces and basements."
    see the Hint?

    in a house with crown moldings with the sheetrock
    walls not taped to ceilings, the crown moldings
    cover up a 1/2" gap on all walls. in every room.
    this one leakage site alone adds up to more
    than all windows & doors.

    this is why we test with a blower door.
    blower door sets up a even pressure against
    all walls so that you can feel during the
    test what you feel when you hav a strong wind
    pushing against one wall.

    so when a homeowner is ready to seal the house
    seriously the following is the recomndation.
    seal big holes first
    seal medium sized holes second
    seal small holes last.
    sometimes when a house is very leaky
    you blower door test..seal holes.
    blower door test again..go identify the smaller
    holes that didn't show up...because of the
    size of the bigger holes..then seal all
    we test homes at 50 pascals (unit of measure used
    nationwide). 50 pa is the ideal pressure to test.
    BUT some homes are so leaky..(multiple tests needed)
    that you can't depressurize to 50 pa, so
    on every blower door is a 'can't reach 50 factor'
    usually on the dials that operate the fan.
    with this factor you take the highest pa you
    reached & multiply it by the factor on the chart.

    by the same token...if a house is tight..which
    isn't as common as homeowners add
    rings to the fan to reduce the amount of air
    the fan pulls from the house. then the
    manometers readings will measure infiltration
    under 2000 cubic feet per minute.

    no one is making this stuff up. it is how
    we test & verify these things and make our

    when I first moved into my house & started
    working with weatherization, I tested my house.
    for 1000 sq ft, my infiltration was 5,400 cfm.
    3/4" gaps behind ceiling moldings...2-3" gaps
    between paneling and floor hidden behind 1/6
    floor moldings.
    countless hours of air sealing & many cases
    of caulk, bags of backer rods, mastic tape ect
    my house is much tighter. having the luxury
    of having my own equipment to verify what type
    of sealing reduced what amount of infiltration
    was a learning experience.

    windows and doors are a part of the sealing
    process...but would be 3rd on the list of 3
    not first.

    take a look at the article. and read
    some of the other articles dealing with
    air infiltration.
    is is good, comprehensive, and educational

    best of luck

  • 11 years ago
    last modified: 9 years ago

    I had read Energy's linked article prior to finding the pie chart. I understood the notion of fixing the largest holes first, but I didn't know where to look for the largest holes.

    I then found the pie chart and I thought it would be useful to use it to prioritize air sealing knowing that it was just a checklist to follow. At least a starting point.

    Honestly, I need to do a blower door test to really find the big holes. I think this is the only way for each homeowner to know where the big holes are.

    Otherwise, we are doing just what Energy says -- sealing the areas that we can feel cold drafts or cold air, but not necessarily addressing the big holes up in the attic or down in the crawl space.

    At this point, I don't think I'm leaking air through the ceiling. I put my hand up there on the crown moldings and by the recessed lights and I don't feel any cold air leaving the space. My ceilings were completely sealed from the inside and I only added the crown molding a few years ago.

    I believe that my air infiltration is from the crawl space. It's not insulated and I haven't inspected the holes for the plumbing.

    Again, a blower door test is needed to identify the big holes. Right now I've air sealed as much as I can feel.

  • 11 years ago
    last modified: 9 years ago

    it is difficult to feel the air leakage at the
    ceiling. unlike walls the wind doesn't blow against
    it. same for floors of homes on piers.

    at best, when hvac system comes pressurizes
    the house, so that would be when you would feel
    a slight leakage at recessed lights.

    but the blower door depressurizes all 6 sides.
    top, bottom & sides of the structure.
    with this depressurization, air is pulled
    into the house via air infiltration sites.

    the oversized cuts in ceiling..recessed lights
    around supply boxes and bath vent fans these
    oversized holes are covered by trims, supply
    grills and bath fan covers.

    so trades make the holes...but don't seal them.
    just cover them up.

    now floors..huge leakage site under bathtubs.
    plumbing pipe cuts are oversized. plumbing
    access are left unsealed.

    my advice to folks is to look for spiderwebs
    as they build their webs where air moves.

    balloon framed walls are never good to
    find. this is a pathway from crawlspace
    into attic. lots of balloon framed walls
    in older homes on piers.

    every house is different but there are some
    common leaks that apply to most homes.

    if you invest in blower door test..have
    ductwork & returns tested. thermal scans
    are nice visuals, but anyone that has tested
    homes for a few years should be able to
    find leakage without thermal scans.

    best of luck

  • 11 years ago
    last modified: 9 years ago

    A blower door test might be the next step to help me find the biggest air leakage area.

    Here's what I've done this holiday season to air seal my house:

    1. Repaired the bottom of my return vent which was open to an unsealed crawl space (dirt ground). I feel better now that my central air is pulling air from inside the house instead of dusty air from under the house.

    2. Closed the fireplace damper and caulked around the frame that holds the fireplace glass doors. This had an immediate impact on cold air drafts in my living room. It made a noticeable difference. It was like having a window open.

    3. Added EPDM rubber weatherstripping to my front door. This also made a difference in the living room in terms of an air draft.

    4. Sealed an unused wall mail slot. The outside had been covered by vinyl siding, but the inside portion was never closed. Air came into the living room from this mail slot.

    I feel that my efforts have made a noticeable impact in the living room with regards to a cold air draft that I use to feel.

    Don't get me wrong, my hardwood floors are still cold and I feel that most of my air leaks/infiltration is coming from the crawl space.

    I still have work to do, but it feels good to stop the easy air leaks.

  • 11 years ago
    last modified: 9 years ago

    you are making progress..that is what counts.

    I've been talking about foam insulating
    my floors. my house is on piers with
    an open crawlspace. but before I can do
    that..have to replace bathroom floor.

    it is always something!

  • 11 years ago
    last modified: 9 years ago

    14 recessed lights here and they were leaking 4-5cfm each on a calm day which after doing the math adds up.

    Baseboard trim and crown moldings usually hide huge leaks and then the ductwork. It makes a huge difference and caulk saves more money than regular insulation.

    I went from leaky ducts and a leaky home built in 06 with a 3.5 ton 13 seer heat pump with 20kw of strips to a 3 ton 15.5 seer with 10kw of strips and have plenty of capacity on 1750 sqft.

  • 11 years ago
    last modified: 9 years ago

    what you want to check is external static pressure
    of ductwork. in an old house (aka leaky house)
    you won't be putting house under negative pressure
    unless you foam insulated walls & attic.
    (hopefully you didn't use cellulose in attic)

    in a perfect world you would have installed house
    wrap or felt in each ceiling joist bay prior to
    sealing. stop the air leakage between paneling.
    at this point...caulking is the only way I know
    to seal these joints between sections of paneling.

    pneumatic caulk gun will push a lot of caulk.
    regular caulk guns will be slower, but give you
    time to use your finger to push caulk into gaps
    & clear off excess.
    keeping a wet cloth that you rinse often will
    keep job neat.
    I use Dap's Alex brand crystal clear 25 year caulk.
    goes on white, dries clear.

    you'll also want to seal penetratoins...recessed lights,
    bath fans, stove fan venting & around openings for
    hvac supply grills. sealing return air is also recommended.

    if house is on piers, then sealing penetrations
    in floors is a good savings. and a good investment
    of your time.

    that is all I have for now.

    best of luck

  • 11 years ago
    last modified: 9 years ago

    can you post some pics of walls,ceiling & floor?
    back in 1888 these were single boards, not the
    sheet goods we have now. (paneling & sheetrock)
    foam spray insulation on roofline and under
    floors would go a long way to air sealing &
    insulating on one step.

    air moving through insulation robs the insulation
    of its R-value. without air sealing...insulation's
    value can be worthless. depending upon where the
    leaks are, and how much leakage.
    blower door testing defined leakage amount and
    location. otherwise, it is like trying to
    fill a bucket with water..and the bucket has holes
    in it!

    I'd love to see what your home looks like from
    the exterior. I have a love of old structures...
    how do you heat & cool this wonderful home?

    any link to your publication?

    best of luck.

  • 11 years ago
    last modified: 9 years ago

    energy_rater_la- just quickly scanning this thread after being off the board over the holidays. Cool stuff- actually Alison B sized our HP system and did blower door testing before and after our remodel several years ago. Unfortunately, the general contractor and HVAC installer ended in fiasco, so I ended up doing lots of sealing after they were out of the picture. Never have gone back and done a blower door on how it ended up. Still a few leaks here and there to be addressed, but generally it's comfortable and we don't have massive utility bills.

  • 11 years ago
    last modified: 9 years ago

    that is pretty sweet that you worked with alison bailes.
    contractor differences aren't uncommon.
    I've caused a few fiascos between homeowners &
    contractors, and contractors & myself.
    hard to get someone who doesn't want to understand
    or change a thing they are doing to comply.
    cauese bad feelings with unwilling folks.

    any of the utility companies near you doing
    blower door testing? it would be great to see
    what you've sealed & discover what needs to be done.

    glad that it workout out..somewhat!
    thanks for the info.