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 1491 Reviews
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.
Anonymous
Easy to install, and instantly stopped drafts and dampened outside noises very effectively!
Robert C
The process could've been smoother with the sending of the measuring kit. There was a delay with weather in Oregon but then it felt like my kit was still delayed due to other reasons. Most new homes (like mine) have textured paint and it can also be inside your window frames. I measured everything out but I still have little tiny gaps due to the texturing. Not indows problem but just be aware you made need to sand or fill in those gaps yourself to get a perfect seal. I did the acoustic grade inserts and they have reduced some noise but they will not completely block or significantly reduce road noise. This is most apparent with deep or lower frequencies like truck exhausts or modified street racing cars that are quite popular these days. Taking the inserts out to open your windows isn't an easy task. The little metal hook they provide needs to be either bigger or you can attach something to it as a way to leverage yourself. Overall the process was average. I think they're definitely a good option for weatherproofing and some sound reduction depending on the type of windows you have. I would purchase again.
Shelley C
The process for ordering and installing the Indow Widnow inserts was so easy. They sent the measuring information and it had great instructions. The inserts were delivered by UPS was crushed on one corner, but the company had packed them well, so there was no damage. We installed them the same day. It works best if you have two people completing the installation. We felt the results immediately and are glad we spent the money to make our home just a little more efficient.
Barry B
The insert fits like a glove and insulates the window! No more frost and condensation on the interior of the window! Thank you for an easy, effective and attractive fix!
Susan A
The support during the entire process was wonderful, thank you so much for the extra quiet space!
Volodymyr R
Very good good quality. Overall very satisfied with this product and service. Thanks
Jane H
Our home was built in 1913 and has beautiful old wavy glass single-paned windows. I’m so glad we were told about Indows and didn’t have to replace the original windows. We live in Canada but had no difficulty placing the order and were very impressed by how accurately the company met its deadlines, including cross border delivery. The Indows inserts blend in perfectly with our home and the existing window frames. You don’t see them unless you’re actually looking for them. But what we did notice was how much warmer the rooms feel the minute the inserts were installed! I can’t speak to any heating bill savings because they just went in this week, but our home feels much, much cozier. Our contractor who took all the measurements and installed the Indows says: “Excellent instructional videos: clear and informative. Very impressed with the design and the product. Overall, the ease of installation is quite impressive. Working with all the staff at the company was great – everyone was very helpful.” I’m already recommending this company to any of my friends who live in drafty older homes and want to reduce their heating/cooling bills and do some good for the environment.
Anonymous
Don't be afraid of buying an older home with single pane windows. This company has you covered. Their inserts are super high quality and fit well thanks to the laser measuring kit they send. Highly recommended!
Katie M
We purchased three Indows to reduce drafts and noise in our bedroom, which faces the street. The improvement was immediate. Our house was built in 1958 and although we have exterior storm windows we didn't want to replace the windows outright due to cost and architectural consistency. These were an excellent solution.
Matthew L
Indow inserts were easy to measure, order and install. They've provided great insulation for old single-pane and stained glass windows in an antique home. We can significantly feel how much better the home holds heat.
Ellis W
I ordered two Indow inserts for my home. They are doing a great job, entirely happy with them and the ordering process.
Elizabeth W
I can't say enough good things about this product and company. Our house is 101 years old and the sidelites next to our front door are single pane ancient wavy glass which means when it gets very cold (Chicago temps) we can have an inch of frost covering the INSIDE of our windows. I was desperately searching for a solution so our front vestibule was not so cold and a friend recommended Indow. The process could not have been simpler and the temperature difference it has made is off the charts.