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Energy Solutions

Comfort and Drafts

Keeping comfortable and saving energy in your home isn't only about insulation

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A Minneapolis Blower Door with DG-700 instrumentation kit — used to measure air-tightness and help with air sealing. Photo: The Energy Conservatory.
Image Credit: The Energy Conservatory
A Minneapolis Blower Door with DG-700 instrumentation kit — used to measure air-tightness and help with air sealing. Photo: The Energy Conservatory.
Image Credit: The Energy Conservatory
This is my house; we still burn 3-4 cords of wood per year, but we're a lot more comfortable than we were before the air-sealing 25 years ago! Photo: Jerelyn Wilson.
Image Credit: Jerelyn Wilson

Insulation is really important when it comes to saving energy in our homes. With more insulation in our walls, roofs, and foundation, less heat escapes via conduction to the outdoors. Insulate well!

All right. That’s pretty clear.

But insulation isn’t everything. There’s also air leakage, which has a huge impact on both energy consumption and comfort. I’m used to embarrassing myself, so let me use our house as an example.

When I bought our house in 1981, it needed a lot of work. Built around 1785, it had been “modernized” in the 1970s, with drop ceilings, shag rugs, fake barnboard siding around the fireplace, brushed aluminum “tiles” around the kitchen sink and stove, tacky modern windows, and extra partitions here and there to create more guest rooms for the Long Island owners and their friends coming to Vermont for ski weekends.

The previous owners had put a lot of money into the house — though almost nothing to improve its energy performance, other than insulating between the floor joists from the basement — and that fiberglass insulation was installed with the facing on the wrong side so that most of it had long since become waterlogged and slumped to the dirt floor in a soggy mess.

I systematically — if somewhat naively — went through the house gutting it room by room, replacing rotted sills, re-siding the exterior, insulating the wall cavities, adding a continuous layer of interior rigid foam insulation, and installing new drywall. When I was done, the walls were reasonably well-insulated (though I would add far more rigid insulation were I doing the work today).

But the house remained incredibly uncomfortable. A few years later, now married and with a baby crawling around on the floor, we had to do something about the discomfort. We heated mostly with wood, and with a roaring fire in the wood stove the room temperature could be in the lower 80s at the ceiling but in the 50s at the floor.

With thick slippers, my wife and I were reasonably comfortable, but when we picked our year-old daughter up off the floor, she was cold! We felt terrible — and worried about her health. The insulation — by early 1980s standards — wasn’t too bad, but the house was anything but comfortable.

Enter the Draft Detective

I did some asking around and hired Dick Cartelli (a.k.a., The Draft Detective) from Putney, Vermont to figure out what was going on. He came in with his “blower door” and tested the home’s leakiness. A blower door is set up in an exterior door frame and turned on to pressurize the house (pictured with this blog is the Minneapolis Blower Door from industry leader The Energy Conservatory). By measuring how much air is being pushed through the blower door and measuring the pressure difference between indoors and out (using two manometers), the operator can calculate the air tightness of the house — usually in “air changes per hour” at the elevated pressure of 50 pascals.

I forget the actual numbers, but the house was leaky — really leaky! Cartelli used two cases of caulk and I don’t know how many canisters of expanding foam sealant, built an insulated attic hatch door with foam gaskets at the edges, and implemented lots of other measures over a week or two to dramatically tighten the old house. By operating the blower door to depressurize the house while he worked, he was able to feel where air leakage was occurring–and seal those holes, cracks, and gaps.

The improvement was dramatic. The delta-T (difference in temperature) from floor-to-ceiling went from over 20° to less then 10°. That delta-T was further reduced when I insulated beneath our floor from the basement and a crawl space. We no longer had to keep the wood stove cranked at full output to maintain reasonable comfort. Our daughter could crawl around on the floor and stay warm (though her earlier experience may have contributed to the fact that she now, as an adult, lives and works in the mild climate of San Francisco!).

The bottom line

Yes, we should insulate our houses well–don’t skimp on adding insulation if you open up your wall system. But we also need to pay attention to air tightness. Drafts cause discomfort and they significantly increase heating fuel use by carrying heated house air up and out, pulling in cold outside air in the process. Adding some types of insulation, such as dense-pack cellulose and spray polyurethane foam, can help to tighten a home, but other measures are often required.

If you have a drafty house, bring in a weatherization contractor to measure how leaky your house really is, and then invest in air tightening. It’s worth it!

In addition to this Energy Solutions blog, Alex contributes to the weekly blog BuildingGreen’s Product of the Week, which profiles an interesting new green building product each week. You can sign up to receive notices of these blogs by e-mail — enter your e-mail address in the upper right corner of any blog page.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.


  1. Mark I. | | #1

    Combatting leakage
    I've only recently shifted from an insulation focus to a leaky envelope focus. I've therefore focused more recently on sealing air leaks in ductwork, walls, windows and doors. I also found recessed lighting airtight trim kits which are a simpler and less costly improvement than switching out the entire can to an airtight model. Two questions: 1) I have a side attic space on the 2nd floor with some dirty spots on insulation that suggest leaks in sheetrock seams. Should I caulk all seams on backside or buy a do it yourself spray foam kit like tiger foam and hit the entire wall. 2) wouldn't bathroom exhaust fans represent a 'leak' and if so does anyone manufacture a 'green' leak-free bathroom fan?

  2. Ken Levenson | | #2

    good for the work crew too!
    What drove home the importance of air tightness to me was our construction site this winter.
    We are doing a Passive House retrofit in Brooklyn Heights currently. The house is uninsulated at the moment but we are at an air tightness of [email protected] (heading hopefully all the way to .6).
    After a sustained week of 18 degree nights and 30 degree days, the workman still did not require that the house be heated - even at the the start of day when it was "coldest". It was completely comfortable because of the passive heat gains (solar, equipment, workmen themselves) were enough given the very air tight nature of the house. It was a revelation to us all on site - feels pretty amazing.

  3. Marie | | #3

    Blower door test
    I just had an energy audit (CT) that was supposed to include a blower door test. They could not do it (although had one done 2 years ago) because the ducts of my forced air system (1952) were encased in asbestos. I was also told they would not do it if there was evidence of mold. But they did do some more caulking in the basement as they had a long caulk spout, that the basic homeowner does not, to get around the multitude of pipes. Just wanted you to know that not all programs/companies will do a blower door test today.

  4. Dave | | #4

    Marie's blower door test
    Your experience made me realize the potential liability of the blower door test. The contractor doesn't want to be responsible for spreading asbestos fibers and mold throughout your home. Did they give you an opportunity to sign a release form to allow them to do the test?

  5. user-723121 | | #5

    Building Airtight
    Vera Novak is running a series this month on infiltration, check out her EcoBuildTrends blog.

  6. Anonymous | | #6

    Weatherization contractor
    I just purchased a home built in 1905. Previous owners sadly replaced the old windows with vinyl ones but I can feel cold air coming from the window moldings. What to do with that? Also where does one find a weatherization contractor? It's cold where I live and NEED one! Look forward to recommendations.

  7. GBA Editor
    Martin Holladay | | #7

    Response to Anonymous
    Here's a Web site that will help you find information on your state's Weatherization Assistance Program:

    If your income is low, you may qualify for free weatherization under the WAP program.

    If your income is higher than the threshold for free weatherization, your state's WAP office should still be able to help you by putting you in contact with local weatherization contractors.

  8. Bill Bradbury | | #8

    PVC windows
    Not only do the plastic windows look terrible and have a short comparative life span, they are generally installed without proper air and water sealing. I am a weatherization contractor and I see this over and over. The blower door often points out that the old wooden windows are leaking less than the new plastic ones because of the air blowing around the frame.
    Another good website to find local energy reduction professionals is Energy Savvy

  9. WEG | | #9

    Sealing Recessed Lights To Stop Drafts
    Here is how a potential customer has fixed his draft problem so he can watch TV in comfort. Before this DIY upgrade ice crystals would form on light fixtures on cold nights.........Hopefully he'll "see the light" and let me seal and insulate.

  10. Marie | | #10

    Marie's blower door test
    No they did not offer a release form to do the blower door test. They explained that it also put them at risk if asbestos fibers got into the air in the house while they were there. I'm glad I had one done 2 years before and I had the paper work to show them. They felt the number from 2 years ago was actually quite good.

    Sadly, they told me it would be $$ impossible to find a contractor to correct the 2 areas needing repair.......a 3 x 5 ft area under the cellulose in the attic where the old boards are cracked allowing warm air to leak up. The second area is a 3 x 3 area in the floor of the closet that has the attic door with stairs. My stairs are stacked. This also impacts the coat closet on the first floor. The best I could do was to lay the silver bubble wrap on the floor (2nd floor) and cut a piece of 2" blue styrofoam to fit the ceiling of the coat closet underneath on the first floor.

    I had tried 2 years ago to gently move the cellulose in the attic where the leak is but couldn't get it all moved without it making a huge mess, nor could I lay myself down enough to caulk the crack as it goes all the way to the roof edge. Sigh. These new energy audit people recommended I lay unfaced fiberglass batts over the cellulose in the effected area. Do you agree??

    Thanks for your great articles!

  11. GBA Editor
    Martin Holladay | | #11

    Response to Marie
    Although additional fiberglass batts can add R-value to your attic floor, they won't do anything to slow air leaks. If air leaks are your problem, then you need to address them with rigid foam board, canned spray foam, or caulk.

    If there are areas that need caulk which you can't reach, canned spray foam might be the best solution. I hope you can find a contractor or weatherization agency who can help you.

  12. Marie | | #12

    Thanks for your
    Thanks for your reply........the cellulose people said they would address the leaks but obviously did not. They said the cellulose would be deep enough to dampen the leaks......They were more concerned about the 12 x 12 area around vent stack and sealing that one.

    I wish now I had never let the roofers drill all those holes near the attic floor as part of the new ridge vent .

  13. Dave | | #13

    Response to Mark I
    Mark - you should seal all the drywall/stud joints. You can use caulk, 1-part foam (in a can) or 2-part foam spray. The caulk is much less messy/costly but will take more time. The 1-part foam can work but gets all over everything and you will need several cans. The 2-part foam REALLY gets all over everything (you should wear a Tyvek suit/goggles/gloves) and is the most expensive. 2-part is mainly used where you want to foam a relatively large area (i.e., all the floor/rim joist areas; "flash" a 1"-thick coating on a wall or ceiling).
    There are better bathroom ventilation fan units with better draft blockers; look for units with the Energy Star certification. You can also install secondary draft stopping devices in the vent lines; has a unique 1-way device made of cloth. You also want to make sure the new fan unit is sealed against the ceiling (caulk/foam) so air does not leak around the housing.

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