What is insulations r-value and how can I calculate it's cost savings?

Use this tool to calculate the differences in efficiency of applying insulation to your room or house. !This tool is still under construction!
Height (m):
Width (m):
Depth (m):
Inside Temp (°C):
Outside Temp (°C):
Wall/Object: Choose a wall (0m2)
Outside Wall:
R Value: (Add up all wall materials using info such as this.)


This room has an area of m2 that it can lose heat directly to the environment. You would need to heat the room by watts to maintain the inside temp.

Why are R-Values important?

The r-values are important as it defines how much heat can escape out of your room or house. The higher the r-value the less heat that can escape out of your house.

The r-value is the thermal conductivity of a material (how well it resists the flow of heat).

Rooms insulated with more material will have a lower thermal conductivity and therefore be cheaper to maintain a comfortable temperature. The savings can add up to large amounts over time.

If you have no insulation adding some can make a world of difference. For example on a solid double brick wall with a width of 3m and a height of 2.4m will require 96 watts to maintain at 21°C. At gas prices of 7p/kWh that costs 0.7p/hour to keep heated or £61.32/year. By insulating the wall when it was being re-plastered the price has dropped to 0.2p/hour or £18.39/year. Saving £42.93 every year in heating.

That was just one wall in one room. Insulating more of your house will mean that the savings quickly add up.

U-values measure the same thing, they just work in reverse with lower values being better.

To convert a u-value to an r-value use the formula: R-value = 1 / U-value.

How to use the tool

To use this tool enter the values for your house or room. Then use the room to select the walls and set the r-value and if it's an outside wall. (Inside walls are ignored).

To calculate an r-value for a wall, add up all the layers. For example a double brick layer has an r-value of ~1.2 and plaster has 0.07. Combine these for 1.27.

To rotate the room please use the arrow keys then click on the rooms values you wish to change.

Contribute or issues

This tool has had to make some estimations and rough guesses to supply it's answers:
  • The tool ignores the heat capacity of the walls themselves and assumes they don't hold any heat.
  • Your room may contain vents other ways fresh air can enter this is not calculated.
  • This tool only looks at the walls leading directly to the outside. Internal walls are not included in the calculations.
  • Currently the tool does not take windows or doors into account.
Contributions are welcome via Github.