Best Energy Efficient Window Types & Costs

Energy efficient windows can help you to save on energy bills all year long. However, you are probably wondering how much you can save per year, and if your new windows can really pay themselves off.

If you have already compared some double glazing offers, you’re now aware that buying new windows isn’t always a simple decision. To recover your upfront investment, you must find a good deal that offers a balance of energy efficiency, cost and quality.

We have written a buying guide to energy efficient windows in the UK, to help you make the best decision for your home – while staying on budget.

• Energy efficient windows can reduce energy bills by up to £235/year in a typical three-bedroom home, according to the UK Federation of Master Builders.
• Triple glazing is even more efficient than double glazing, but also 10-20% more expensive. In many cases, the additional energy savings don’t make up for the higher price.
• uPVC windows offer energy efficiency at an affordable price. However, aluminium and timber windows add more home value.

What Are Energy Efficient Windows?

Compared with traditional windows, energy efficient windows have a higher resistance to heat flow between their interior and exterior surfaces. Efficient windows work in both directions, which means two things:

• They reduce unwanted heat loss during winter.
• They reduce unwanted heat gain during summer.

In other words, installing energy efficient windows is like improving the insulation in your home. This means you save on space heating during winter and air conditioning during summer. Energy efficient windows use double or triple glazing, which has an air gap that reduces heat loss. Many windows also include additional efficiency features like low-emissivity coatings (Low E), inert gas between their glass panes, or a combination of different methods.

Any double-glazed window is “energy efficient” compared with older single-glazed windows. However, providers normally use the term “energy efficient windows” to describe glazing with low-E coatings, inert gas filling, or an energy rating of A or higher.

How Much Can You Save With Energy Efficient Windows?

The energy savings you can achieve with new windows depend on several factors. For example, efficient glazing saves more in a large home, simple because you are upgrading more windows. Your potential savings also depend on the type of windows you are replacing. For example, a homeowner who upgrades 30-year old single glazing can expect higher savings, compared with a homeowner upgrading 15-year old double glazing.

In 2016, the Energy Saving Trust conducted a study of the potential savings achieved by A-rated, B-rated and C-rated windows. In all three cases, the calculation assumes an upgrade from single glazing. We have updated the original savings table in the study to account for the energy cost increase between 2016 and 2023. The table provides the estimated savings for different property types:

You can see the original savings calculated by the Energy Savings Trust by clicking on this link. These calculations are based on energy costs from 2016.

How Much do Energy Efficient Windows Cost?

The typical UK home can save up to £235 with energy efficient windows, but we also need to know their cost to determine if they will pay off. uPVC windows cost between £371 and £972 according to the Federation of Master Builders. As you might guess, the most efficient windows are at the upper end of this price range.

Here are some typical price ranges for double glazed windows with different frame materials:

Keep in mind these are general price ranges to be used as reference. Fitting and labour costs vary widely by home, and they can represent up to 60% of the price of a window upgrade. To get an accurate quote, you need a home assessment by a professional window installer.

In the table below, we have estimated the long-term savings you can expect when using energy efficient uPVC windows, considering a lifespan of 25 years. We also compare those savings with the upfront cost:

As you might expect, installing energy efficient glazing is more expensive in large homes with more windows. However, the energy-saving opportunity increases in the same proportion.

Note that the figures in the table are rough estimates based on typical window prices and annual savings. Actual results can vary widely by home, depending on architectural features and energy usage habits – hence the importance of a professional assessment.

Having covered the typical cost of energy efficient windows and the savings you can expect, we will now discuss the technical features that make their efficiency possible.

Understanding the Energy Efficiency of Double Glazed Windows

The energy performance of windows depends on multiple factors, which include: heat conductivity, spacing between the glass panes, frame material, glass coating, air tightness, etc. To make purchase decisions easier, glazing manufacturers use the Window Energy Rating or WER, which scales from “E” for the least efficient windows to “A++” for the most efficient. The WER was developed by the British Fenestration Rating Council (BFRC).

The Window Energy Rating uses a combination of other ratings, which describe specific aspects of window performance.

G-Value: Solar Heat Gain Coefficient

The G-value describes heat gain through a window when exposed to sunlight. The G-value uses a scale of 0 to 1 to indicate solar heating:

• A G-value of 0 indicates that the window blocks solar heating.
• A G-value of 1 indicates that the window allows a full transmission of solar heating.

The G-value is a tricky performance metric. Solar heating is beneficial in cold climates regions like the UK, since it reduces the workload on space heating systems. This means that windows with a high WER have a high G-value. However, solar heating is counterproductive in warmer climates, since it makes air conditioners work harder. In these cases, a low G-value is more beneficial.

Energy efficient windows designed for the UK have a high G-Value, typically above 0.40.

U-Value: Heat Transmission Coefficient

The U-value is an indicator of heat loss through your windows. Double glazing with a low U-value can retain indoor heat more effectively, which means you spend less on space heating. Here are the typical U-values for different types of glazing according to Everest, a leading window provider:

• Single glazing = 4.8 to 5.8
• Double glazing = 1.2 to 3.7
• Triple glazing = Less than 1.0

For example, a single-glazed window with a 4.8 U-value will lose four times more heat, compared with a double-glazed window with a 1.2 U-value. Triple-glazed windows have an even lower U-value, but they also come with a higher price tag.

To summarise, energy efficient windows have a low U-Value.

L-Value: Air Leakage Coefficient

The L-value of a window describes its airtightness. A low L-value indicates that the window prevents air leaks, while a high L-value means the window is a less effective barrier. Leaky windows are very detrimental for home efficiency, since your heating system works harder to compensate for the continuous heat loss.

Many modern windows are fully airtight, which means their L-Value is zero.

Window Energy Rating (WER)

The Window Energy Rating (WER) combines the three window efficiency metrics described above: G-Value, U-Value and L-Value. The technical details are complex, and you can read more about them at the BFRC website, but here is a quick summary of how each metric affects the overall efficiency:

• Higher G-Value = Higher WER
• Lower U-Value = Higher WER
• Lower L-Value = Higher WER

The British Fenestration Rating Council (BFRC) considers that a window is efficient if can take advantage of solar heating (high G-Value) while having low levels of heat loss (low U-Value) and air leakage (low L-value). The BFRC calculates an efficiency score with the following formula:

• BFRC Rating = 218.6*G – 68.5*(U+L)

This value is used to determine the WER rating of windows, according to the following table:

For example, a double-glazed window with 0.45 G-Value, 1.2 U-Value and 0.0 L-Value would have the following BFRC rating:

• BFRC Rating = 218.6*0.45 – 68.5*(1.2+0.0) = 16.17
• Based on the scale above, this would be an A+ rated window (BFRC score of 10-19)

UK building regulations require C-rated windows or better. You are not forced to upgrade your existing windows if they are less efficient, but any new windows you purchase must be at least C-rated. However, it makes sense to purchase more efficient windows (A to A++) to save on energy bills.

Window Design Features that Determine Energy Efficiency

We have discussed the energy efficiency metrics of windows. Here are the actual design features that lead to a high efficiency.

Glazing

The type of glass has a direct effect on the energy efficiency of windows. Triple glazing is the most efficient, but double glazing tends to offer the highest return on investment. Double glazing is only slightly less efficient than triple glazing, while being much more affordable.

Low E Coatings

Energy efficient windows often use coatings that reduce their heat emission, making them a more effective thermal barrier. Low-E glazing reduces the U-value of windows, driving up their energy rating. Window manufacturers also use glass coatings for other purposes such as UV protection.

Frame Material

uPVC, timber and composite frames are the most efficient, since they have a low heat conductivity. Aluminium frames are more conductive, which makes them less efficient overall. However, modern aluminium windows include energy efficiency measures such as thermal breaks and insulation.

If you are concerned about maximum return on investment, uPVC frames offer a combination of high efficiency and low cost.

Inert Gas Filling

Some double-glazed windows improve their efficiency by using an inert gas layer between their glass panes. Double glazing is normally filled with air, but better insulation is possible by using inert gases like argon, krypton and xenon.

Now we have covered the typical costs and savings of energy efficient windows, while discussing their energy ratings and technical features. By now you might have a better idea of what to look for, and we can provide some buying tips.

Balancing Cost and Savings to Ensure a Return on Investment

Some windows have a very high efficiency, but you must also pay attention to costs. From a financial standpoint, moderately efficient windows that will pay off are a better purchase than top-efficiency windows that will never make up for their price.

uPVC vs Timber Frames – Both options are energy efficient, but uPVC frames are much more affordable. While a typical uPVC window ranges from £372 to £961, a timber window ranges from £1,147 to £1,829. High-quality uPVC windows can last for more than 25 with minimal maintenance needs. Timber windows can last for over 60 years, but they are very demanding in terms of maintenance.

• uPVC windows are recommended if you are concerned about recovering your investment.
• Timber windows may be a better option if you plan to sell your home in the near future, since they add more value to your property.

Double Glazing vs Triple Glazing – Triple glazing has a higher efficiency, but the extra savings are often not enough to cover the higher cost.

• Triple glazing is recommended If you want to reduce your energy consumption and carbon footprint as much as possible, regardless of cost. Installing triple glazing makes sense as an environmentally conscious decision, but you may not recover your investment.
• On the other hand, double glazing is recommended if you are concerned about breaking even or earning a return during the lifespan of your windows.

Argon vs Krypton vs Xenon-Filled Windows – Inert gas-filled windows offer a higher efficiency, but you should pay attention to the specific gas. Argon is the most cost-effective option, and recommended if you want to recover your investment. Krypton is more efficient but also more expensive than Argon. Xenon is the most efficient of the three inert gases, but Xenon-filled windows are both difficult to find and very expensive.

Getting a Good Deal on Energy Efficient Windows

If you’re installing new windows, you want to know if they will pay themselves off. As we have discussed in this guide, there are many design features that improve the energy efficiency of windows, and prices can vary widely.

Before meeting with a salesperson, you should know what you want and how much it should cost. If you go into the meeting uninformed, you might end up paying for something you don’t need, extending the payback period of your new windows.

If you’re ready to upgrade to energy efficient windows, we can help you find the best deals. Use our free comparison tool to find the top window installers in your area and save up to 37.5% on your double glazing.

Now read:

What Are The Best Soundproof & Noise Canceling Windows? How Much Do uPVC Windows Cost in 2026? How Much Do Aluminium Windows Cost in 2026? How Much do Timber Windows Cost? Anglian Windows Review 2026