What are thermal windows?

Thermal windows are designed to resist the passage of heat from inside to outside, or vice versa. Many thermal windows accomplish this by having a pocket of air in between two pockets of glass. Those of you familiar with how Indow Windows work will recognize this – Indow Windows thermal inserts install inside your window frame with our compression tubing, which means an air seal is created allowing for this insulated pocket of air.

What is heat transfer and why does it matter?

Thermal windows primarily serve to regulate thermal comfort. An article by Energy Vanguard on the 4 Factors of comfort reveals that the following factors influence thermal comfort:

•    Temperature. How hot or cold is it? Humans like to be in the range of 70 to 80 degrees, more or less. This is the most obvious of the 4 factors of comfort and gets the most attention.
•    Humidity. How much moisture is in the air? Forty to sixty percent relative humidity is the ideal range. In addition to decreasing comfort, a relative humidity that’s too low or too high increases the likelihood of things like bacteria, mold, dust mites. (See the diagram below.)
•    Air Movement. Is the air moving across your skin? In the summer, one way that our bodies keep cool is by the evaporation of sweat. A nice breeze or a ceiling fan can keep us comfortable even when the the temperature and humidity are at or above the narrow range we find most comfortable. In the winter, that same air movement will make us uncomfortable.
•    Mean Radiant Temperature. How hot or cold are the surfaces around you? Of the four factors of comfort, this one’s the least recognized or understood, but let me give you a couple of examples. If you’ve ever sat next to a window on cold night, you’ve probably experienced discomfort due to a low mean radiant temperature. The cold inner glass surfaces suck heat out of your body because you’re radiating heat to them but they’re not radiating much back.  This can happen even with double pane windows!  Another mean radiant temperature problem occurs in bonus rooms, where you can have walls with a hot attic on the other side. Most of the time those attic knee-walls are poorly insulated and thus get very hot. Even if the air temperature in that room is 70 degrees, you may be uncomfortable because the walls keep blasting you with heat.

Tell me more about this radiant heat transfer and how it affects me!

Think about sitting down in a room to read your favorite book. If you had a nifty infrared thermometer, you would find the temperature of your chair, the book, yourself, your walls, the floor, and the windows would all be drastically different. Even though your thermostat may say 70 degrees, you may feel as if  it is way colder than that!

Colder surfaces will suck the heat right off of warm surfaces, most importantly you! Instead of turning up the thermostat to combat this process, insulation and air sealing measures may be used. One of them being thermal inserts for your windows.

This theory was recently tested by Portland State University’s Green Building Research Lab. They found that Indow Windows thermal windows cost effectively reduce heating energy consumption by approximately 20% by delivering superior comfort that kept homeowners from dialing up their thermostats.

The report states, “The fact that the average measured savings was nearly double this  (at 19%) might be a direct result of the thermal comfort benefits of the Indow Windows. Specifically, since the interior window surface of the Indow product is much warmer than would be the inner surface of the single pane of glass, the occupant within the building will feel warmer standing next to the Indow Window, than standing next to a single pane of glass even if the room air temperature is the same in both cases. As a result, the occupant is more likely to operate their home heating system at a lower thermostat setting after the Indow Windows are installed.”

If you are still hungry for information on the topic, we have some great resources for you:

Healthy Heating: Mean Radiant Temperature (A mathematical view)
PSU Report on Thermal Windows
Naked People Building Science