Glass IQ · Your climate, your glass

Winter frost. Summer heat. What is your glass doing to your home?

Pick your city and your windows. See where water and ice form in winter, how much healthy humidity your glass allows, why it feels cold near the window, and how much sun heat pours in all summer, side by side with a Passive House triple pane.

Pick a region, then your city. The page adapts to your climate: winter cold, summer heat, or both.
New build? Pick your current spec or a competitor's quote. Replacing windows? Pick what's installed now. Glass thickness: about 4–6 mm single, 16–28 mm double, 32 mm and up triple.
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Dew point indoors. Any glass colder than this collects water; below freezing it turns to frost.

Every common glazing type, same conditions

Bars show the inside temperature at the bottom edge of the glass, the coldest spot and where water forms first. Anything left of the dashed line is wet.

Dew pointLuxHaus Passive House triple

Healthy humidity, or dry windows. Pick one?

Health researchers recommend keeping indoor air at 40 to 60% humidity. Yet in cold climates, homeowners are told to drop to 30% or lower all winter. That advice protects the windows, not the people. A better window removes the trade-off.

Highest humidity your windows allow
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With the LuxHaus Passive House triple
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Healthy range, 40 to 60%Usual cold-climate advice, 30% or lowerYour setting
Dry air weakens your defences. In a Yale study published in PNAS (Kudo, Iwasaki et al., 2019), mice kept at 10 to 20% humidity fought off influenza far worse than mice kept at 50%. Dry air slowed the clearing of virus from the airways and slowed tissue repair.1
Public health experts aim for 40 to 60%. Public health physicians and researchers interviewed on the Yale findings recommend 40 to 60% indoors. Below 40% brings dry eyes, dry skin and easier virus transmission.2
The 30% advice comes from the windows. Canadian utilities advise 30 to 35% in winter specifically to reduce condensation on windows, and building scientists use a rule of thumb of 30% or lower once it is below freezing outside.3, 4

Why a cold window feels cold, even at 22 °C (72 °F)

The thermostat measures air. Your body also feels the surfaces around it. A cold pane takes comfort away in two ways.

Convection: the draft with no leak

Room air touching the cold glass cools down, gets heavier and sinks. It pours off the window and slides across the floor. You feel a draft on your ankles even when the window is perfectly sealed.

Radiation: the cold that pulls heat from you

Your body radiates heat to every surface it faces. A cold pane absorbs more of it than the warm walls around it, so the side of you facing the window feels chilled, like standing next to an open freezer.

See the draft

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Your windows–
LuxHaus Passive House triple–
Same room, same 22 °C (72 °F) on the thermostat. Left: ordinary glass, cold air sliding off the window and across the floor, frost on the pane, radiator running. Right: Passive House glass, barefoot by the window, no radiator.

Draft speed at ankle height, by distance from the window

Your windowsLuxHaus Passive House tripleDraft limit, 0.15 m/s (30 ft/min)

Cold air speed from the Heiselberg downdraft model for a cold vertical surface, using the glass-to-room temperature difference on the design day.5 Comfort standards treat about 0.15 m/s at the ankles as the point where people start to feel a draft.6

Your windows on the design day
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colder than the room air
LuxHaus Passive House triple
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colder than the room air
Passive House comfort limit
5 °C 9 °F
keeps downdraft and radiant chill below what people notice, with no radiator under the window

Passive House in 90 seconds

Five ideas that make a house comfortable in any climate

1 of 5

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Prefer a video?

Passive House explained in 90 seconds

A short independent explainer by Pinwheel Passivehouse. Opens on YouTube in a new tab.

Passive House explained in 90 secondsPinwheel Passivehouse · Watch on YouTube ↗

Passive House window check

Passive House requires the inside window surface to stay at or above 17 °C (62.6 °F) on the coldest design day, with 22 °C (71.6 °F) indoors. That is the 5 °C (9 °F) limit above, written as a rule. It also sets which Passive House window class your climate falls in, and the U-value limits that come with it.

Passive House window class–
Certified window, max–tested at the standard 1.23 × 1.48 m size
Installed window, max–including the installation joint
LuxHaus––

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Your design temperature
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Maximum installed window U-value for comfort
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LuxHaus Passive House triple
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WindowInstalled U-valueInside surface on design dayComfort criterion

The class here is estimated from the city’s winter design temperature. The Passive House Institute’s own climate data sets the official class, which can be one step stricter or looser (Vancouver, for example, is Cool-temperate there). Your Passive House consultant confirms it.

Southern US · Mexico · Caribbean · GCC

In warm climates, the enemy is the sun.

Every window does three things with sunlight: it bounces some back, absorbs some, and lets the rest into the room. The infrared that gets in is heat your air conditioner has to pump back out. The ultraviolet fades floors, fabrics and art.

Using your windows: – Change

1What kind of home?
2How much glass does it have?
I know my glass area
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3Where is most of the glass?
4Any shade outside?

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Your windows–
LuxHaus triple, solar-control–
Same room, same thermostat setting. The sunlight through the glass is the difference.
Your windowsWhat happens to the sunlight
LuxHaus triple, solar-controlWhat happens to the sunlight

Summer: does your glass sweat on the outside?

On humid nights, air conditioning chills the glass from inside. If the outside of the glass drops below the outdoor dew point, water forms on it: fogged views, streaks and dirt that sticks. Triple glass keeps its outer pane at outdoor temperature, so it stays clear.

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Adjust outdoor humidity
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Outdoor dew point: glass colder than this line gets wetLuxHaus

Outside glass surface on a calm, humid summer night: outdoor air minus the temperature drop across the outside surface film (0.08 m²·K/W for still night air) for the heat the air conditioning pulls through the glass. Outdoor conditions are typical humid-night values for each city. On a cool, clear morning in temperate climates, dew can also form briefly on the outside of very well insulated glass; it is a sign the glass insulates well and clears within the hour.

Typical published values for each glass type; certified values vary by product, and LuxHaus confirms them per project. Sunlight carries roughly 53% of its energy as infrared, 44% as visible light and 3% as ultraviolet. Glass area is estimated from the home size and how much glass it has (window openings of 12%, 20% or 30% of floor area, less 20% for frames). Blinds and curtains are not counted. Sun on each side at 9 am, noon and 4 pm on a hot summer day: west up to 750 W/m², east up to 700, south up to 450; the tool uses the hottest hour.

Next step

What does this window spec cost over 25 years?

Window IQ turns these numbers into money: the heating and cooling bill, replacement cost and the total 25-year gap between your current windows and LuxHaus triple pane.

Window IQ: homesWindow IQ: commercial
Traffic, airport or city noise? Glass also decides how quiet the room is. The Acoustic Planner gives the sound rating your project needs, room by room.
Open the Acoustic Planner →

Get this report for your project

We'll email your results with the numbers for your location, plus:

  • The latest order date for your install, including European production and shipping
  • The glazing and frame combination that clears the comfort criterion in your climate
  • A firm estimate when you upload your plans and window schedule
Plans and window schedule (optional)

    We use your details and files only to prepare your report and estimate, and to follow up on this project. Your details are stored securely in our customer system (HubSpot) and your files go to our team by email. You can ask us to delete them at any time. Privacy policy

    Thank you

    Sources: 1. Kudo E, Iwasaki A, et al. Low ambient humidity impairs barrier function and innate resistance against influenza infection. PNAS 2019;116(22):10905. 2. CTV News, interviews with public health experts on indoor humidity. 3. ATCO Energy, best humidity for your home. 4. Green Building Advisor, ideal relative humidity in winter (RDH Building Science rule of thumb). 5. Heiselberg P. Draught risk from cold vertical surfaces. Building and Environment 1994;29(3):297–301. 6. ISO 7730, ergonomics of the thermal environment: local thermal discomfort from draught.

    How this is calculated: condensation is checked at the bottom edge of the glass, next to the spacer, where water forms first. Edge temperatures use typical temperature factors (fRsi, ISO 13788) for each window type; center-of-glass temperatures use an interior surface resistance of 0.13 m²·K/W (ISO 6946); the dew point uses the Magnus formula. Design temperatures are approximate winter values for each city. Results are planning guidance only and do not replace an engineered assessment, your Passive House consultant or the local code official, whose requirements govern.

    Glass IQ v4.3

    About Glass IQ

    Compare a standard double-pane window with Passive House triple-pane glazing for your climate: heat retention, solar heat gain and noise reduction. Free, no login.

    Who it is for

    Homeowners, architects and builders choosing glazing for a new build or renovation.

    How it works

    1. Pick your climate.
    2. See standard ENERGY STAR double pane next to Passive House triple pane on heat retention, solar control (low-E coatings) and noise reduction.
    3. Use the result as a planning guide before specifying a glass make-up; LuxHaus offers several hundred glass combinations.

    Frequently asked questions

    Is triple-pane glass worth it?

    In cold and mixed climates triple glazing cuts heat loss through the glass by roughly half compared with good double glazing, removes cold drafts and condensation near the window, and is quieter. In hot climates the solar control coating matters more than the number of panes.

    What is the difference between Ug and Uw?

    Ug is the center-of-glass value; Uw is the whole window including frame and spacer. Codes and energy bills follow the whole-window value.

    Do triple-pane windows reduce noise?

    Yes, especially with asymmetric or laminated glass. For a room-by-room estimate use the Acoustic Planner IQ.

    More free LuxHaus tools

    Quote X-Ray IQ · Window Code Check IQ · Residential Window IQ · Commercial Window IQ · Acoustic Planner IQ · Lead Time Planner IQ · All tools

    LuxHaus Windows & Doors supplies high-performance European windows and doors factory-direct to North America, the Caribbean, Mexico and the GCC. Submit your plans or ask Emma, our 24/7 AI advisor.