Idaho’s climate is hard on windows. Across the southern part of the state, the yearly temperature range is wide. Pocatello’s 1991-2020 normals run from an average January low near 17°F to an average July high near 90°F, and nearby Twin Falls follows a similar pattern. When one room feels cold by the window in winter and another feels stuffy by mid-afternoon in summer, most homeowners adjust the thermostat first. Nu-Vu Glass regularly helps Idaho homeowners who find that their windows are contributing to the problem. Feeling cold near a window does not always mean air is getting through it.
The Cold You Feel Is Not Always Moving Air
A warm body gives off heat toward nearby cold surfaces, even when the surrounding air is warm and still. Building scientists call the combined temperature a person experiences the mean radiant temperature, and a cold pane can pull it down.
Lawrence Berkeley National Laboratory compared several window systems with the outdoor temperature at 0°F and indoor air at 70°F. The resulting interior glass temperatures varied sharply by glazing type:
- Single-pane glass: about 17°F
- Clear double glazing: about 45°F
- Low-E double glazing: about 56°F
In one example from the same analysis, the mean radiant temperature near single-pane glass was about 53°F while the room air remained at 70°F. Turning up the thermostat cannot eliminate that radiant chill. The room air may be warm while the glass remains much colder.
Where Drafts Come From
Air leakage is a separate issue from the surface effect above. With age and repeated seasonal temperature changes, weatherstripping can flatten, seals can deteriorate, and gaps can develop around the frame. A failed insulated-glass seal is different again: it can reduce the unit’s thermal performance and often appears as condensation or fogging between the panes.
How Summer Heat Gets Through Closed Glass
In summer, the direction reverses. In an Idaho home, a west-facing room can receive a large amount of solar heat through clear glass in the afternoon even when the morning felt comfortable. The SHGC shows how much heat from incoming sunlight passes through the glass. A lower value limits that heat gain. Low-E coatings can reduce SHGC, but the best value depends on the window’s orientation, shading, and exposure to winter sun.
What To Check on the Window Label
When comparing ‘energy-efficient’ windows, Idaho homeowners can read two numbers on the NFRC label.
- U-factor: how well the window insulates. A lower number means less heat loss.
- SHGC: the fraction of incoming sunlight that becomes heat inside the home.
ENERGY STAR sets window performance thresholds according to climate zone. Under Version 7, products in the Northern zone must have a U-factor of 0.22 or lower and an SHGC of 0.17 or higher. Idaho homeowners can check their county’s zone before using those figures to compare windows.
What Inefficient Windows Can Add to Energy Use
The U.S. Department of Energy reports that heat gained and lost through windows accounts for 25% to 30% of home heating and cooling energy use. That makes window performance one part of household energy use that homeowners can easily overlook.
The most suitable combination depends on the window’s orientation, surrounding shade, and exposure to direct sunlight. A window also needs to be measured and installed correctly to deliver the performance shown on its label. Even a well-rated unit can underperform if the frame is out of square.
When a room stays cold in winter or overheats in summer, the windows deserve a closer look. U-factor, SHGC, glass condition, and installation can affect how comfortable an Idaho home feels.
