During client consultations I explain IGUs have four numbered surfaces, and here’s a bit of trivia I toss out when we’re customizing: on a double-pane unit in a heating-dominant climate, do you prefer the low-E on surface #2 or #3, and why? Bonus points if you’ve noticed comfort or condensation differences in a north-facing bedroom when it’s about 20°F outside.
I usually spec ‘low‑E on #3’ for north bedrooms in heating zones; the room-side lite runs a touch warmer at 20°F and I see less perimeter sweat if it’s paired with a warm‑edge spacer. What RH are you seeing in that room — on south/west elevations I switch to #2 to keep SHGC down, but on true north it’s mainly about interior surface temp.
Leaning #3 for north rooms at 20°F — I’ve measured a 3–4°F bump in room-side glass temp with argon and a soft-coat using a $25 IR gun, which cuts edge draft and morning fog. I only spec #2 when I’m chasing SHGC on south/east; on a true north wall there’s nothing to harvest. @james_derrick91 what interior RH are you seeing in those bedrooms?
I get better comfort with #3 in that scenario, but the real fix for perimeter sweat was pairing it with a stainless warm‑edge spacer and a full 1/2-in argon cavity. If it’s a sunny south bay I’ll flip to #2 for the extra gain — @m_lopez58, do you notice shade position changing the outcome?