GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Casement vs. double-hung windows: Cost vs. air leakage

pgh_sean | Posted in Energy Efficiency and Durability on

I’m looking at a whole home replacement window project.  I’m going to use Provia vinyl windows.  I keep reading that if energy efficiency is a main concern then hung windows are not an option.  “Casements or tilt and turn must be used because they have the best air leaking ratings.”  I’m also seeing that over time hung window air leakage will degrade.  All of that being said, the air leakage ratings on the double hung windows seem fantastic to me.  U factor (.19) and SHGC (.27) are identical.  (The house isn’t oriented to take advantage of south facing windows so high SHGC is not desired.)

Test Specification – ASTM E 283

Double Hung
Air Leakage – .05 cfm/ft2 @ 25 mph

Air Leakage – .02 cfm/ft2 @ 25 mph

1. This seems like a tiny difference.  Would anyone expect a perceptible difference standing by the window or on energy usage?
2. Is the degradation of the double hung air leakage a considerable factor over time?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Dana Dorsett | | #1

    You could do the math on the energy cost difference (but I wouldn't sweat it.)

    A high SHGC makes a measurable difference on heating energy use even on north facing windows, but can increase cooling costs on unshaded east or west facing windows.

    1. pgh_sean | | #2

      Thanks Dana. The long sides of the house face East and West so I guess there's not a lot of opportunity to take advantage of solar hear energy. The North and South sides of the building have minimal windows.

  2. PeterGBADemo | | #3

    Hi Sean -

    I have never seen double-hung windows with air leakage that low. I checked the NFRC Certified Product Directory ( for Novia double-hung and under air leakage it simply has < (or equal to) 0.3 cfm/sf, what is required in the IRC 2015 code.

    Sure sounds good, but hard to believe!

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |