Energy Efficient uPVC Windows

So you’ve made the decision to insulate your loft, walls and have changed to Solar Power, a choice that will save you money and help to protect the environment by providing free energy and reducing our reliance on fossil fuels. But why stop there?..

If you are going to be heating your home with your free solar energy, why not retain the heat within your home by installing A+ rated uPVC windows and composite doors? Not only will energy efficient glazing keep you warmer by minimising heat loss, it will also save you money by protecting your investment. You’ve insulated your loft, now insulate your windows…

What makes an energy efficient window?

Window energy ratings are calculated taking into consideration a range of variables including heat loss, air leakage and solar gain.

1)      Heat loss – Heat loss is the amount of energy that is able to escape from your home through both conduction and radiation.

2)      Air leakage – this is the measurement of how much air your windows are allowing to leak from your home, taking with it heat energy

3)      Solar gain is the measure of how much of the sun’s natural heat energy is allowed to enter your home, therefore allowing your home to gain free heat energy, thus reducing the need for additional heat sources during daytime hours.

These factors are tested by the BFRC (British Fenestration Ratings Council) and a window is allocated a window energy rating which is an indication of how efficient the window’s performance is when used with a particular glazing specification. uPVC windows are rated from G up to A+ rating; A+ being the highest performing windows and G being the least energy efficient.

Window Energy Ratings

What is heat loss?

Heat loss is quantified as a u-value and is measured in kW loss per m2 of window area per year, the lower the u-value the more efficient your windows will be. Here is a brief history of u-values over the decades an how u-values have improved:

  • 4mm Single Glazing: u-value 8.0
  • 28mm Double Glazing: u-value 4.0
  • 28mm Pilkington K-glass Double glazing: u-value 3.0
  • 28mm Pilkington K-glass Double Glazing, argon gas filled: u-value 2.8
  • 28mm Planitherm Soft coat double glazing, argon gas filled: u-value 1.4
  • 28mm Planitherm Soft coat double glazing,  argon gas filled, warm edge spacer bars: u-value 1.2
  • 36mm Planitherm triple glazing, krypton gas, warm edge spacer bars: u-value 0.8

How can a window reduce heat loss?

High quality uPVC windows and composite doors are designed to minimise heat loss by combining a range of design factors. These are explained here

1)      Multi-chambered extrusions – The multi-chambered design of our uPVC case frames and opening sashes means that there are several air gaps protecting the internal warm air from the external temperatures, this vastly reduces conduction as air is a highly effective insulator.

2)      Double and Triple glazing – Either 28mm double glazing or 36mm triple glazing can be used as glass units, these provide air gaps inside of the sealed glass units that are argon gas filled. This dense, inert gas is used in place of air, the denser the gas, the better it will perform as an insulator. Argon is 4x denser than air and mush more stable, providing a large layer of insulation between the cold external glass pane and the warm internal pane. This both reduces heat loss and stops convection of cold air around the glass, thus stopping draughts.

3)      Thermal Spacer Bars – Separating the panes of glass are spacer bars, traditionally made from hollow aluminium to house desiccant, these would conduct cold from the external pane of glass and reduce the temperature of the internal glass pane, leading to cold spots. This can be seen by condensation forming around the perimeter of the glass on cold days. To combat this a new composite material is used which does not conduct the cold, this is known as WarmEdge spacer bars, usually coloured black to make them less obtrusive.

4)      Low Emissivity Glass (low-e glass) is a term that describes glass that has thermally efficient coatings to reflect heat radiation, this stops the vast majority of heat from escaping, thus reducing heat loss. Several forms of low-e glass are available, the most efficient of which is ‘soft-coat’ low-e glass such as Saint-Gobain Planitherm glass.

5)      Thermal reinforcement has now replaced steel and aluminium frame reinforcement, this is again acts to reduce the conduction of cold which leads to heat loss. Thermal frame reinforcement is far more thermally efficient than metal reinforcement while retaining the strength.

How does a window minimise air leakage?

uPVC casement windows are designed to be as air-tight as possible. There have been several generations of uPVC window extrusions, starting in the late 1980’s, the profiles are continually being redeveloped as new technologies are introduced that can increase the performance concerning air leakage and thermal insulation.

1)      Dual elastin gaskets and weather seals are used in the extrusion of only the best quality uPVc profiles. Elastin is a material that will not shrink and deteriorate over time like traditional gasket materials such as neoprene.

2)      The co-extrusion of such gaskets means that the gaskets are extruded in situ as the uPVC profiles are extruded. This means that the gaskets are part of the frame extrusion rather than being pulled though after, this ensures a consistent seal on opening window sashes.

3)      Windows with fully reinforced window case frames and opening sashes will suffer far less expansion and contraction than windows that do not have reinforcement during extreme temperatures. Reinforcement ensures that large profiles will not bow or twist which can lead to the weather seals and gaskets not making a consistent seal with the frames, this therefore minimises air leakage and maximises energy efficiency.

4)      Windows that are both surveyed and fitted by experienced windows fitters will have a much better seal, using only the best materials to seal the frames in the brickwork apertures ensures that no air can leak around the parameter of the frames.

Window Heat Loss

How can I maximise solar gain?

Solar gain is referred to as g-value (gain value), this measures the solar heat energy that is able to pass through a glass sealed unit into a property. The solar gain reduces the need for domestic heat sources such as radiators while the low heat loss of the windows means that the heat is not lost.

1)      Low-iron low-e glass is used on the external glass pane of a double or triple glazed unit, this allows heat waves to pass more freely into the property while still blocking harmful uv radiation and keeping the maximum light to pass through the glass.

How much do replacement A+ rated uPVC windows cost?

The cost of replacement uPVC windows depends on the number of windows as well as the size and opening configurations. Some properties may be limited on the opening configurations to comply with FENSA regulations for fire escape. Some example prices are shown below, there are no hidden extras but no building works are included in the below prices such as rendering or lintel alterations, both of which are no usually required. You can of course personalise your installation with decorative glazing options, bespoke window colours, etc; these options can be priced separately.

Energy Efficient Windows Doncaster | Window Energy Ratings Doncaster

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