There are several reasons why triple glazed sealed window units are more expensive than double glazed units. Firstly, an extra pane of toughened glass is fitted, which means there is another chamber to be filled with argon gas, and an additional spacer bar. In addition, due to the increased size and weight of the unit, the transport costs will also be higher.
The cost is worked out as a simple extra sq.m. cost over double-glazing that usually comes to about £100 per sq.m. This equates to an average 4 foot (1220mm) window having around one square metre of glass. This adds up to a cost of around £100 for a double-glazed window of average size.
What is the Cost of a Triple-Glazed Window?
Even though we have a vast range of window choices with many different systems and material options at KJM Group, let’s just look at a standard white uPVC double-glazing system with a couple of openings. The installed value of this example, including VAT, will be around £465 (correct cost as of July 2019). The equivalent system in triple-glazing will come to around £565 which amounts to a 22% increase in cost.
Heat Loss Through Windows and Triple Glazing
Houses in the UK typically lose about 20% of internal heat through the windows. Therefore, the most sensible thing to do when changing your windows is to fit the best, insulated systems you can afford. Of course, the extra cost of fitting triple glazing will have to be offset against the savings in heating bills and payback cannot be expected to occur overnight. However, as related to us by one of our customers – “we feel that triple-glazing is the right window system for us because we would like to live as comfortably as possible”. Ultimately, the final decision is yours to make.
The Benefits of Triple Glazing
Although there are many benefits to having triple glazing installed in your home, mainly for heat insulation, it is important to remember that not all triple gazing is equal. In order to get the maximum benefit from triple-glazed systems, it is important to ensure that the gaps between the glass panes are at least 16mm and filled with inert argon gas to reduce heat loss. If the gap is less than 16mm, the thermal performance of the unit will be reduced, unless a more expensive gas like krypton is used.
The ideal specifications of a triple glazed sealed window unit should be 4mm of glass panes with 16mm gaps in between. In the glazing industry, this is known as a 4/16/4/16/4 unit, equal to 44mm in total. Simply comparing the u-values (loss of heat) of the window panes, you will see that the difference between a 44mm triple glazed unit compared to a double glazed unit of 28mm is quite large. Considering that the typical u-value of a centre pane in a 44mm unit is 0.62 while it is 1.1 in a double glazed unit, there is more than a 40% improvement.
Triple Glazing Energy Rating
Many people choose a window unit based on how many glass panes it contains. However, a more reliable way of predicting the thermal efficiency of a window system is to take a look at the WER (Window Energy Rating). Window Energy Ratings are the standard method in the UK for calculating how much heat is lost through window panes.
Window Energy Ratings take the following into account:
- The loss of air through the window panes.
- The u-value, which calculates the thermal efficiency of the entire window system, including the glass and frame materials.
- The amount of heat from the sun that passes through the window panes to warm up the home. Generally, triple glazing has no enhanced solar gain compared to double glazing. A well-insulated triple glazed window system retains heat well but does not enhance solar gain to any degree.
Triple Glazing Cost Summary
So it turns out that, according to our above calculations, triple glazing can cost up to 22% more than double glazing. However, this only takes into account our costs at KJM. Generally, if our prices are compared to a national glazing company, for example, our costs for double and triple glazing units will be a lot cheaper. Some larger companies sometimes offer ‘free upgrades’ for triple glazing, however, you should always consider what the starting point is for the ‘base’ product. For example, if the starting price is doubled then a 50% discount will bring it down to a sensible starting point! When dealing with this type of circumstance, in my opinion, it is always worth getting another quotation to compare starting costs.