Sep 13 , 2022

What Is The U-factor? How To Select?


What Is The U-factor? How To Select?

The U-factor, or thermal transmittance, of a window or door, is the main factor determining how well your home stays warm in the winter and cool in the summer and it's not just about windows and doors.

The U-factor also refers to the ratio of heat flow through glass, meaning that factors such as framing, glazing, sealants, etc., will all affect the U-factor of your window or door. So here's what you need to know about thermal transmittance, so you can make smart purchasing decisions to keep your home comfortable year-round.

What Is The U-factor?

When shopping for window treatments, it's easy to get swept up in all the beautiful options and forget what factors into your decision. U-Factor is a measurement of heat loss through windows and other glazed areas.

Window treatment retailers use many names for this crucial metric, but don't let their terminology confuse you. Technically, the correct term should be Window U-Value Factor. For example, if a window has a U-value of 1.0 on its surface and an emissivity index of .8, 20% of the heat that escapes through that surface will escape by radiation.

Windows with lower values are better at trapping heat than those with higher values because they lose less energy by radiation. Window u-value (often abbreviated WU or U-factor) describes how well heat energy in a room is kept inside.

An excellent way to think about it is like a dollar bill: one with fewer zeros keeps more money in your pocket than one with more zeros. For example, an energy-efficient double pane window may have a uU-value of .35, while another new double pane will have a U-value of .25 for 20% less heat loss.

What Is A Good/Bad U-Factor Score?

U-factor score may not seem like a big deal, but it's one of the essential elements in window selection. Ideally, you'll want a rating below 0.4 for your glass – anything higher may allow too much heat transfer and lead to an inefficient home. It's also important to note that these numbers can vary based on where your windows are located; side windows will typically have a lower score than front or back.

The same goes for windows facing south, as they receive more sun exposure and will be warmer than those facing north. The main point here is that if you're trying to minimize your heating costs (which we all should be), it's crucial to find a low-U-factor window with energy-efficient features like argon gas insulation, triple pane construction, and laminated safety glass.

What Are The Benefits Of A Low U-Factor?

1. The lower the U-factor, the better the thermal insulation of a window or door will be.

2. As a bonus, low U-factors mean less energy will be needed to heat and cool your home.

3. A lower rating also means less energy consumption by the equipment inside and outside your home responsible for providing hot water and heat during cold winter and cool air in summer months.

4. Simply put, a low U-factor saves you money on energy bills year-round. Choosing windows with a low U-factor is not only environmentally friendly but can also save you thousands of dollars over time.

Whether looking for new windows or doors, selecting ones with a low U-factor should always be one of your top priorities. There are many other benefits to having low U-factor windows or doors; however, these four points alone should convince anyone how important this feature is.

How To Choose U-factor According To Your Location And Climate?

The first thing you'll need to do when selecting insulation is deciding what climate zone your home falls into and what the prevailing temperature of your area is during different times of the year. There are two components of insulation: R-value (measured in ft2 degrees F/BTU) and U-factor (measured in BTU/ft2degreesF).

R values help insulate against heat flow, while U-factors help insulate against cold. Generally, homes located in warm climates should be fitted with insulation with a low U-factor. In contrast, homes in colder climates should be equipped with insulation with a high U-factor.

Low U-factor insulation will save on heating costs for those living in warmer areas because it prevents the inside of the house from getting too hot. High U-factor insulation will reduce energy costs for those in colder regions because it keeps the inside of the house from getting too cold.

In addition, there are four types of materials that can provide thermal resistance: fiberglass batts, cellulose, mineral wool, or polyurethane foam boards; each material has its pros and cons that we have detailed below so that you can select what is best for your needs.

Cellulose insulation comes as either loose fill or sprayed-in-place varieties. Loose fill provides less air space than other types of insulation and may produce a dusty mess if not installed correctly.

Sprayed-in-place also produces a dusty lot, but because it fills every nook and cranny more thoroughly than loose fill, it's much easier to install without creating airborne dust. It also provides superior fire protection qualities compared to other types of insulation. Mineral wool or Rockwool is made from molten rock combined with water vapor at around 3,000°C, then spun into long fibers, which are compressed into board form.


In conclusion, insulation helps improve a home's energy efficiency by reducing heat transfer across walls and ceilings. U-factor can be used as a general rule when choosing insulation for your project because it gives you an understanding of how well the material resists heat flow.

It's worth noting that all materials in this category will eventually degrade, and many types of insulation are available on the market. To find out which is best for your project, please consult a professional or review the products with specifications listed on the manufacturer's website.

Once you know what kind of insulation is right for your needs, consider purchasing at least twice as much product than needed so you'll have enough material left over to complete the job.

What Is The U-factor? How To Select?

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