Exterior Doors

Doors come in a variety of different sizes and building materials, with windows or not, and all from an amazingly wide array of manufacturers. Choosing the best entry door for your home can be a daunting task with the plethora of data available.

However, the most important – and overlooked – quality of a new door is how well it saves energy.

While buying the cheapest door on the market may be good on your checkbook at first, it can eat away at those savings in a hurry if the door is not up to the standards for your local climate. I once bought a vinyl sliding glass door from Home Depot because of the price, only later to regret it once I realized how leaky it was.

Entry doors are notorious for leaking air and heat, either through their windows or poorly-fitting jambs. As energy costs continue to rise, this can end up costing you thousands over the course of a couple of years.

EnergySaversGuide.com has analyzed thousands of data points to find the best entry doors for your area.

The Use of Climate Zones

The US Department of Energy (USDoE) has broken the United States up into eight major climate regions, with additional sub-regions based on average rainfall.

Every three years, the IECC map is adjusted to move certain counties into and out of different climate zones. The latest was released in 2021. These climate zones are used to determine recommended energy-saving qualities of entry doors. The minimum values of U-Factor (heat loss) and SHGC (solar heat gain) for each climate zone are set by the USDoE.

This means that depending on your climate region, it may not make sense to simply buy the most expensive entry door on the market. The added cost of a more energy-efficient door may be wasted if your local climate is mild, such as many of our southern states.

Conversely, northern “colder” states may see their energy costs rise if their doors do not meet or exceed recommended values. It is very possible that the cost savings earned by buying cheaper doors will be eaten up by increased energy costs.

Understanding the NFRC Door Label

The National Fenestration Rating Council (NFRC) label helps you compare between energy-efficient windows, doors, and skylights by providing you with energy performance ratings in multiple categories.

While ENERGY STAR labels just tell you if a product is energy efficient or not, NFRC labels tell you how efficient they actually are. The different climate regions within the United States have specific ranges each of these values need to fall in between to be considered energy efficient.

The NFRC certifies that each entry door that carries its label has undergone independent verification by an accredited lab.

U-Factor measures how well a product can keep heat from escaping from the inside of a room. The lower the number, the better a product is at keeping heat in.
Range: 0.20–1.20
Look for: Low numbers

Solar Heat Gain Coefficient (SHGC) measures how well a product can resist unwanted heat gain, which is especially important during summer cooling season. The lower the number, the less you’ll spend on cooling.
Range: 0–1
Look for: Low numbers

Product Details are listed on the left-hand side of the label, and list the different models for that particular door. This includes the description of the door frame and/or glass.

Glass Area is listed at the top of each column, showing the amount of glass in the door by area. As a door’s total glass area increases, so will its need for energy saving precautions. Many doors will have different versions of the same door with varying amounts of “lites” or windows.

An example door NFRC sticker

Energy Savings by Door Type

SteelPolyurethane FoamR5 – R6
FiberglassPolyurethane FoamR5 – R6
Wood(none)R2 – R3

R-values show how well a product is at insulating. Higher R-values are preferable for colder climates, and door types make a huge difference.

Steel / Fiberglass Doors

Steel doors commonly have magnetic weatherstripping that completely seal off any possible air leakage areas. Solid wood doors are poor insulators, and they do not have the added benefit of a polyurethane foam insulating layer. This added insulation make steel and fiberglass doors the best at conserving energy. For example, a 1-1/2 inch thick door without a window offers more than 5 times the insulating value of a solid wood door of the same size.

Doors with Windows

As doors add “lites” or windows, their R-value begins to drop precipitously. Glass is an extremely poor insulator as well, so finding a door with multiple layers of glass and low-e coatings will be a good investment, especially in colder climates.

Sliding / Patio Doors

Sliding doors are usually problematic at conserving energy. The fact they slide means that they simply cannot be air-tight like a typical hinged door. Air leakage is a common problem with all sliding doors. Air leakage is calculated as a cubic feet per minute (cfm/ft²) value, and sliding patio doors generally are about 6 times worse at preventing the leakage than hinged doors.

In addition, sliding – or patio – doors also usually have larger window areas. As we explained above, as the window area increases, the less efficient it is at insulating.