Whenever you’re considering buying new windows or evaluating the effectiveness of the ones you already have installed, you should take into account radiant heat gain and loss.

Radiant heat refers to heat radiated into your home by the sun and heat radiated out of your home from the objects and people inside. This is due to the phenomenon known as thermal radiation, which dictates that heat flows constantly from warmer things to cooler things. What this means is that during the winter, the warmth in your home is constantly trying to escape to the cold environment outside. During the summer, the heat outside is constantly trying to flow into your cooler apartment.

This heat exchange affects your home’s energy costs. If your windows aren’t retaining heat effectively during the winter, you’ll pay the price in heating costs. Similarly, if your windows aren’t efficient at keeping out heat during the summer, your cooling costs will shoot up.

Generally speaking, a household that doesn’t manage heat flow appropriately won’t be very comfortable to live in, either. It will be too cold inside in the winter and too warm inside in the summer.

By applying an understanding of radiant heat gain and loss to the way you shop for windows, you can make your home more energy efficient, save big on those energy bills, and dramatically increase the comfort level of your home.

Heat Always Seeks Cold

Basic thermodynamics teaches that heat follows cold. But you don’t need to be a physicist to understand the principle. Heat is energy that seeks equilibrium. Whenever there is an imbalance in temperature between one space and another, heat tries to escape toward cold to level things out to an even temperature. Radiant heat gain and loss occur as a result. But what does any of this have to do with windows?

Windows are critical avenues through which heat enters and escapes your home. In the winter, the heat in your home tries to escape through them to the outside of your house, where it’s cold. Likewise, in the summer, the hot summer air tries to pass through them to take refuge inside your cold house. Radiant heat gain and loss cause your heating, ventilation, and air conditioning (HVAC) to cycle, continuously having to work to keep up with changes in temperature.

Your windows are some of your home’s first lines of defense against the more severe forms of radiant heat gain and loss, which can cause your energy bills to skyrocket and your home to become uncomfortable. You should invest in windows that are resistant to heat flow—windows that will keep heat in during the winter and out during the summer.

Check the U-factor

In order to find the best windows for your household’s energy needs, you should pay close attention to U-factor. U-factor is a nationally recognized measure of how energy efficient a window is—or, more precisely, how effectively it resists heat flow. Displayed upon all National Fenestration Rating Council (NFRC) labels, U-factor ratings range from 0.20 to 1.20.

The lower a window’s U-factor, the more resistant it is to radiant heat gain and loss. Windows with low U-factors will keep excess heat from escaping out of your home or into it, resulting in a more comfortable living environment. What’s more, they will keep your heating and cooling systems from expending more energy than necessary to keep your home’s temperature in check, saving you a great deal of money on energy costs.

So if new windows are on the table, bear in mind the science behind heat flow and browse for windows with low U-factors. As far as windows are concerned, it pays to invest in energy efficiency. The windows most resistant to radiant heat gain and loss are the best options for saving you money on energy costs and keeping your household a comfortable temperature year-round.