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Air sealing or new HVAC system conundrum

Sam Dhak | Posted in Energy Efficiency and Durability on

guys –  I am in the North East and have a pretty poorly installed low-efficiency 20 year old HVAC forced-air system that’s broken down a few times. It does both heating via furnace & cooling. The home also has some average pink batts insulation in the attic. Our home is 100 years old and it has a new roof but no insulation in exterior stucco walls but does have 2-pane windows. Currently, the attic system powers the 2nd floor while the basement system powers the basement & 1st floor. Instead of putting band aids in, I’ve decided to take the right steps to air seal, provide better air quality and, better efficiency during both cold and warm months given we plan to live here at least 10+ years. I’ve compared our energy bills for both winter & summer and we are at least 30% higher than homes that have more work done with insulation and 2-stage HVAC systems

 
Here’s the problem – I’ve read that to do it right, you must air seal first, then insulate and then only can you come up with the right HVAC load needed after performing a blower door test. In my case, if I air seal the attic using best possibly blown-in insulation, won’t ripping out the hvac system from the attic destroy some of the blown-in insulation that would need to be repeated?

Also, does somebody have some links on what air sealing entails – all I can think of is attic, all doors and that’s it – what else is there to it? I want to be educated before I call the local air sealing contractor. I’m in NYC if anybody has recommendations

Thanks

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Replies

  1. jkonst | | #1

    There are a number of good articles on this site that are probably worth a read. I'm not an expert, so I'll let those members chime in with more specific advice, but the articles below helped me better understand air sealing. By the way, 475 High Performance Building Supply is in NYC where you (and I - hi from Downtown Brooklyn) are. Might be a good resource for you, as well.

    https://www.greenbuildingadvisor.com/article/top-10-air-leaks-in-existing-homes-part-1
    https://www.greenbuildingadvisor.com/article/is-air-sealing-mostly-bs
    https://www.greenbuildingadvisor.com/article/a-roundup-of-air-sealing-products
    https://www.greenbuildingadvisor.com/article/whats-more-important-air-sealing-or-insulation
    https://www.greenbuildingadvisor.com/article/air-sealing-an-attic-in-a-cold-climate

  2. GBA Editor
    Kiley Jacques | | #2

    Hi Sam,

    You are right to want to focus on air sealing—it’s likely the best thing you can do to your house in terms of energy efficiency. You asked for some links to better understand key locations. Here is a link to GBA’s collection of posts related to air sealing. There are so many aspects to it that I thought I should share all of our related resources.

  3. Sam Dhak | | #3

    Ok thanks for the links but none of them help me solve my conundrum on this question

    Here’s the problem – I’ve read that to do it right, you must air seal first, then insulate and then only can you come up with the right HVAC load needed after performing a blower door test. In my case, if I air seal the attic using best possibly blown-in insulation, won’t ripping out the hvac system from the attic destroy some of the blown-in insulation that would need to be repeated?

  4. Jamie B | | #4

    Sam,

    To answer your question: You don't need to do a blower door test to determine the size of your new hvac system. The blower door test is to know how air sealed you arem nothing to do with the load calcs. You need to hire an hvac engineer to do a heat loss/ heat gain calculation, it's called a Manual J (don't ask me why its called that)

    So when your hvac engineer is doing your manual J, you can tell that person what new insulation you're putting in and that you're going to air seal vigorously. That along with all sorts more info, that person will determine the HVAC load.

    Then do the HVAC, then blowin afterwards. (Assuming you're redoing all your ducts?)

    I'd also like to point out dropping in blown-in insulation is not air sealing. Not sure what you meant but that's how I read it.

    Hope that helps,

    Jamie

  5. Sam Dhak | | #5

    I clearly feel there is a cold draft of air coming in through these window corners. I have already changed the felt but not sure what else can I do to block the air coming in

  6. Expert Member
    Zephyr7 | | #6

    Is the draft due to air leakage around the window, or convection currents (cold "falling off" the surface of the glass)? A smoke stick is a sort of poor-man's version of a blower door test for small issues like this so you might use that to localize the leak you're feeling.

    If you've already replaced the seals and you're sure they're installed correctly (not folded over or jamming anywhere), and if this is a temporary "over the winter" concern, try some rope caulk around the perimeter. I use rope caulk myself around some older sliding glass doors that I have to help keep a good air seal over the winter. Rope caulk can be pulled off easily in the spring when you want to use the door (or window) again.

    Bill

  7. Jamie B | | #7

    Sam,

    Sliding windows are notorious for leaking. It's inherent in their design. Casement windows are way better for air sealing.

    Proper Air sealing is mostly done in the building phase. Ie caulking around framing or taping the seams of the sheathing etc.

    When the house is already built, there are some cheap things you can do, they help a bit. Things Like sealing around can lights at your ceiling. And foaming the back of electrical outlets and switches.

    then that's are more expensive things you can do. Like replacing all your windows to triple pane casements, and your exterior doors to european style doors. Or when changing your siding, taking the opportunity to air seal the exterior sheathing.

    Watch some Matt risinger videos on air sealing. You can learn a lot from him. I have.

    Also consider if you're going to make your house super tight, you have to consider ventilation. You'll need a balanced ventilation system like an HRV as well.

    So assuming you're not going to majorly overhaul your house, so stick with sealing the can lights and comment to the hvac engineer about a moderate leaky house in your manual J. It'll compensate for that.

    I get it, we all want to be efficient as possible. But to get to 0.5ach probably isn't possible without a lot of money and time and to which the payback could take like 50 years. To which we can argue is ultimately less efficient.

    I'm making number up though, but I'm probably not far off. If you want to get quotes on window and doors and siding, the new hvac system and then bring them back here, there are others on GBA that could actually show you how to crunch the numbers.

    I hope this helps.

    Jamie

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