Your home will lose about 20 percent of the heat lost through its windows. That’s a lot. So how do you reduce the amount that’s lost and drop the costs to your electricity bill? First, you need to understand how heat escapes before you can fix it. After understanding the problem, you will find that storm windows are the most cost-effective way to improve the energy efficiency of your windows.
The second law of thermodynamics states that heat flows from a hot body to a cold body. In the summer, the heat outside your home is trying to make its way in and in the winter the warm air is trying to escape to the cooler outdoors. There are three different ways that heat travels – radiation, convection, and conduction. Radiation doesn’t apply to heat loss from your windows, but convection and conduction are the main means that the warm air in your home uses to escape during the winter.
Convection is the movement of heat by way of gas or liquids. If you have a crack in your window or the seal around the window, then warm air will find its way through. About 35 percent of the heat lost in a home is due to convection as air escapes through all of the tiny cracks in your home – through your windows, doors, outlets, roof, and several other areas. If you have noticeable cracks in your windows, it’s probably time to replace them. But even if you don’t see cracks in your windows or the seal around it, you may still be losing heat due to conduction.
Conduction is the transfer of heat from one warmer molecule to a colder molecule. Once that molecule is warmed, then the heat transfers to another colder molecule. If you accidentally leave a metal spoon in metal pot that is cooking on top of a stove, conduction will occur and your spoon will get hot quickly. If you left a wooden spoon in the same pot for the same amount of time, it would not be nearly as hot when you touched it. This is because metal conducts heat much better than wood.
In physics, the U-Value is the amount of heat transmitted per hour through a square foot of material when there is a one degree temperature difference on either side. Metal has a higher U-Value than wood. The inverse of U-Value is R-Value. R-Value is a measure of a material’s resistance to heat flow. A key point to understand is that R-Values can be added together. If a material with a R-Value of one is placed on top of a material with an R-Value of two, their combined R-Value will be three.
So why did you need this short physics lesson? You can improve the R-Value and reduce the amount of heat transferred through your windows by attaching storm windows to the interior or exterior of the primary windows. By adding a storm window onto an older with a low R-Value, you may be able to achieve the same R-Value as a brand new, energy efficient window. Replacing windows can be very expensive. On average, it costs about $10,000 to replace all the windows in your home. Adding storm windows will cost you a fraction of what a replacement window would cost and will improve the energy efficiency of your windows by reducing the amount of heat that can enter and exit through them as a result of conduction.