is vacuum glazing worth it ?

is vacuum glazing worth it ?

June 28, 2023

Over the last few years there seems to be a big marketing campaign by companies located in mainland Europe and the far east about pushing their vacuum sealed glazing range. While their claims of an lower U-value is certainly impressive, there is also a number of issues that would ask the question, is vacuum glazing really worth the cost?

lets start with a few small points. there is many claims about the low U-value of 0.7 but what is not well known and they certainly don’t advertise it, is that this U-value is only the centre pane U-value and this drops considerably towards the edge of the pane even more compared with Slim double-glazing. This is important when installing into Georgian style sash windows

this type of glazing can be lower than that of the main fabric of the building, in particular in historic buildings. This causes a real and present danger of moving the dew-point to the (stone and timber) walls, leading to interstitial condensation, potentially trapping moisture in the walls, causing it to degrade, in particular when non-breathable plaster and paint has been used

Appearance : As per photo shown the black spacers, mirco dots etc . A vacuum system requires spacers to keep the two panes apart, many people don’t realise how noticeable these are, imagine looking out at your window and forever seeing black dots, also the grey lines at the edge called the Getter which will also be seen when glazed

Cost : The cost of vacuum glazing currently sits around £320m2, meaning a standard double hung sash window could be up to £1000 to glaze with vacuum glazing compared to around £300 for Slim double-glazing. But lets drill down into that a bit more as the manufacturers of vacuum glazing claim that the extra cost will all be worth it. so using the below formula we can calculate the costs

how do you calculate how much money your glazing will save from the U-value ?

Let’s say you have a glazing to put in the living room that is 2 metres wide and 2 metres high. Average unit of Slim-Glaze double glazing is 4/6/4 and has a U-value of 1.5Wm2K and you are considering vacuum glazing that has a U-value of 0.7Wm2K.

To calculate how much money you will save on heating lost through the double-glazed window you follow the steps below.

  1. Work out the difference between the two window U-values (1.5 – 0.7 = 0.8Wm2K)
  2. Multiply that number by the window area (0.8 x (2 x 2) = 3.2)
  3. Work out temperature difference inside and outside your home (21DegC – 4DegC = 17)
  4. Multiply the temperature difference by the U-value area (3.2 x 17 = 54.4)
  5. Divide that number by 1000 to convert it into kilowatts per hour (54.4 / 1000 = 0.0544kWh)
  6. Multiply that by 24hrs in a day and 365 days in a year to get your annual kWh (0.0544 x x 24 x 365 = 476.54kWh)
  7. Multiply that figure by the cost of a kWh of gas (476.54 x 8.1p =£38.59 per year, of heat lost through that window)

This is a slightly crude calculation as there are always other factors involved, but from Slim double-glazed window in your living room with vacuum glazing will save you perhaps £20 per year in heating bills, assuming you heat up your home for half the year in the cold months.

In short, there’s only a small payback and that extra £700 per window will take half a lifetime to even pay for itself. and many home-owners do not want this extra cost in an cost of living crisis