R-Value and U-Value: What Value Are They to You?
If you’ve never purchased or repaired windows, you might not know what you need when that time comes. It seems like there are countless window types to sort through. Comparing window ratings is a good starting point, but even then it’s not crystal clear. R-value vs U-value? Is one more important than the other? And what is a good score? Here we break down R-value vs U-value and help you figure out where to go from there. After all, a straightforward problem like warming your home should have a straightforward solution.
What Is R-Value?
R-value is a score given to a barrier – such as a wall, roof, or window – based on its ability to resist the flow of heat through it. Think back to elementary school when we learned about heat conductors and insulators. Can you recall copper as one of the best examples of a heat conductor? Heat passes through it easily. So copper would make a very bad wall. For your home’s “shell” (building envelope), you want something that resists heat transfer. The R-value (the ‘R’ stands for “resistance”) will tell you how well different barriers will resist that transfer.
In the US, you will see R-values ranging from 0 to 66. Higher numbers mean better resistance to heat transfer. While R-values can be assigned to any surface of a building envelope – roof, ceiling, floor, wall, window – it is important to think about the role a surface plays in your home.
Walls are well-insulated and meant to protect against the outside elements. Windows should insulate, but also be able to open and let fresh air in. Windows should also be transparent for visibility and sunlight. For this reason, comparing the R-value of an insulated wall to the R-value of a window is not a good teller of insulation qualities. Compare the R-value of walls to that of other walls; compare the R-value of windows to the R-value of other types of windows.
What Is the Best R-Value for Windows?
A single-pane window will have an R-value of 1. A standard double-pane window will have an R-value of 2. While a single-pane window with an R-value of 1 does not offer great insulation, you get a much better picture of its performance by comparing it to a double-pane window than to an insulated wall.
Some specialty windows that are highly insulated can reach an R-value of 5. This is great insulation, but the downside is the cost. Replacing multiple windows with these specialty windows will cost you thousands of dollars.
It is no secret that windows are the weakest spots in a building envelope when it comes to insulation. No windows will be able to insulate as well as the walls and roof of your home do. The aim is to increase their R-value and U-value as much as possible.
| Performance Data | Single-pane Window | Double-pane Window | Indow insert + Single-pane |
|---|---|---|---|
| Thermal Insulation (R-Value) | R-1.0 | R-2.0 | R-1.87 94% of Standard Double-pane |
What is U-Value?
U-value, or U-factor, is a score given to a surface based on how quickly it allows heat to pass through it. U-value can be thought of as the opposite of R-value. If R-value tells us of a surface’s thermal resistance, then U-value is a surface’s thermal transmittance. ‘R’ stands for resistance. For U-value, think of ‘U’ in circUlation, a word that has a similar meaning to “transmittance.”
But make no mistake: when it comes to winter insulation, a good U-value is given to a surface that transmits heat as slowly as possible. A good U-value does not indicate a surface quickly allowing heat to pass through it.
U-value scores typically range from 0.1 to 1. The lower the U-value, the better. A single-pane window has a U-value of about 1. This means it allows heat to pass through it quickly. A standard double-pane window has a U-value of about 0.5.
R-Value vs U-Value
While we say that R-value and U-value are opposites of each other, there are some differences that we should discuss. Traditionally, U-value was used for windows and R-value was used for the other surfaces of a building.
R-value tells us how well a surface resists heat transfer. U-value tells us how quickly or slowly a surface allows heat transfer. Radiative heat from the sun has a much greater effect on windows than it does insulated roofs and walls, so that is taken into account with U-value. As a result, you can expect a window’s U-value to change based on time of year and time of day.
Calculating for R-value and U-value is easy. Dividing 1 by the R-value will give you the U-value:
R-value = 1/U-value
Dividing 1 by the U-value will give you the R-value:
U-value = 1/R-value
How Can You Improve Your Windows’ R-value and U-value?
If you have an historic home with original windows, replacement is not an option. It can hurt the historic value and many historic districts do not allow window replacements. Maybe you don’t have the ability to take on an expensive window replacement project. You can improve your windows’ R-value and U-value without replacement.
Indow window inserts can be placed inside your window frames to improve the insulation of your window openings. When paired with single-pane windows, Indow inserts can improve the R-value to 1.87, or 94% of a double-pane window! With a double-pane window, the R-value will be improved even more. When paired with a single-pane window, Indow inserts will improve the U-value from 1 to 0.53. That is a huge improvement in insulation without the cost, time, or effort of a replacement project.
To see more performance data of Indow inserts and to learn about the various insert grades Indow offers, download our Product Data Sheet.
The Product Data Sheet also includes useful information on fit and egress compatibility with your windows.
Customer Reviews
4.49 Average 1505 Reviews
Anonymous
WE just took delivery of the two window inserts we ordered. they both fit perfectly. The most difficult part of the process was me trying to hold the laser measuring device still while taking the diaginal measurment! The Indow team was helpful and the ordering process was catch free. the finished product is just as they described. once installed, you can not even tell that they are there. I will warn you, if you have larger sizes they will come in a pretty large packing crate/box to protect them so be prepared. The only reason for 4 stars insted of 5 is they have just been istalled and we shall see how effective they are at reducing cold air, but they fit so snug that I anticipate they will be very effective. Just in time too, because our area is in a low temp/low wind chill pattern at the moment.
Craig F
The Indow I ordered was a perfect fit. It looks great and is an extremely well made product. The ordering process was seamless.
Catherine J
Noise reduction by at least 50%! I cannot hear most car that drives by now. My bedroom is so quiet! Thank you!
Walter M
Easy to order and install.
Dianne F
Window inserts help with sound since I live facing the street and the highway
Dianne
This is a 5 star company from beginning to end. I purchased the I inserts in 2017 because the bedroom on the second story faced the street. These are very effective for street noise. Noticed a problem on one of the windows recently and they quickly took care of it due to their warranty. Customer service personnel are very helpful. The price of the windows was acceptable for top quality of sleep and less noise during the day
Charles C
Recently purchased the acoustic window inserts for a couple of old windows facing a busy street and they've made a huge difference in terms of noise reduction! The measuring process was relatively easy with the laser measuring tool that Indow sent and the windows were delivered faster than expected. Martin was easy to work with and we would highly recommend Indow to those looking for window inserts.
Dean C
Installed noise canceling acrylic Indow window inserts to deal with the road noise at my condo, 4 lane state road is 40 feet from the condo. Expensive custom fit, but oh my gosh, they cut the noise by 75%! Decibel meter app I trust shows a 6 Decibel noise reduction, average Db over 30 minutes. Turns out 6 Db is letting only 25% of noise through! I am one happy camper…
Harry T
The Indow team was great from start to finish! They were very clear about each step. After installing the inserts my home has been significantly while still preserving the fabulous city views. For anyone who lives in a noisy street or city like NYC I would highly recommend it. Leave the chaos outside and come home to piece and quiet.
Paula S
From start to finish, we were very pleased with our rep, Reed, and the other staff at the PDX will call! The inserts themselves are stupendous! We purchased six total for the noisiest, road side(s) of our home. The outcome was beyond our expectations! Not only did the three rooms that bordered the road become at least 70% quieter, the other end of our home did as well! I cannot recommend Indow inserts more! The technology makes sense to add the inserts rather than purchasing new windows. Great results and thank you! Paul and Paula Spilsbury
JD
Brian was very helpful & informative. He helped me order the correct windows for my needs. They were shipped with the utmost of care & arrived ahead of schedule. Ultimately, the Indow Windows have been very helpful in muffling unwanted noises & they have helped save on our energy costs. Thank you, Indow Window!
Cynthia M
Very happy with the reduction in noise. Easy to install and use. Great customer service.
Juli E
We are thrilled with our Indow window inserts! I'd been on the lookout for a more permanent solution to leaky windows in our third floor living space. I discovered Indow on social media but since then have learned of friends who'd had Indow recommended to them by their rennovation contractor. The entire process went smoothly with friendly reps at hand to talk through questions during measuring, etc. They fit perfectly and help us to maintain the beautiful design of the windows on our 100 year old home! Highly recommend!!
Jen F
Worth the money!
Elizabeth H
For townhouse living, this solved my problem with noise from my neighbor's with my kitchen window. A considerable decrease of noise indeed! Measurements were a bit frustrating so I recommend using a laser measurement device and following directions to use a string for the diagonal. They look great and were easy to push into place. I highly recommend as an alternative to buying a new window.