New to this and wondering if any of you DIY experts can give some advice. We have some old double glazed units in our house, which appear to have been badly fitted - draughts etc . Some of these units are also failing, with condensation appearing in between the panes. We don't have the skills to fit new windows ourselves so have had some reputable (well as reputable as dg companies can get) out for quotes. While the quotes don't seem unreasonable, we are baffled by the choices. Our house is cold in winter but tends to get hot in the south facing front in summer. Although a rated windows sound great for the winter, we are concerned about the downside of possible overheating in the summer. We already need to keep the curtains closed in one south facing upstairs bedroom (that has a huge bay window) in hot, sunny weather due to overheating. One dg suppler uses planitherm on the inside and self cleaning glass on the outside panes. Another was selling planitherm on the inside and low e on the outside - this option seemed to offer the best u value A 8 as opposed to A 5 for the planitherm and self cleaning glass. The installer selling the planitherm and low e said that the low e would keep heat in in the winter but deflect the sun in the summer. Does anyone know if this is right or have any ideas as to the best option to go for, or any alternative ideas as to what to look for when getting our windows replaced? Our house gets pretty cold in winter and anything that makes it a bit warmer is welcome but, by the same token, we don't want rooms to become unbearably hot in the summer.
As you will now be aware, there are a vast range of glass coatings available which are made to meet different needs. A rated windows using an energy efficient glass like Planitherm are ideal for most small domestic windows. A rated windows are very energy-efficient in that the coating on the glass captures solar heat energy from outside the property, allowing transmission through the window unit. The coating also helps keep heat within the room so removing heat loss. A rated windows actually have a + score under the Window Energy Rating scheme meaning that they actually allow a net gain in heat (i.e they bring in more heat than they lose). This is a significant step forward versus more traditional double glazing.
For larger south-facing windows I would suggest an energy-efficient glass such as Planitherm on the inner pane with a solar control glass on the outer pane. This would ensure the that energy-efficiency of the windows is maximised whilst reflecting a good proportion of the solar heat entering the unit, maintaining a comfortable temperature in the room. For ease of maintenance it is possible to buy a solar control outer pane with self-cleaning attributes which will mean you need to clean your windows less frequently too.
Have you considered an alternative solution? I've recently had a SAP survey done on some insulated shutters and the results were quite impressive. U-value of 0,81W/m²K and a heatloss saving of 55%. The advantage for you would be onthe south facing window where you would be able to take advantage of solar heat gain in the winter and shut it out in the summer, not something that double glazing can do. Just a thought.