why does my double glazing get condensation on the inside

Open the bathroom window or use the extractor fan when showering. Keep the bathroom door closed at all times, to prevent water vapour from showers circulating around the flat. Use a cooker hood (venting directly to the outside) when cooking every litre of gas burned produces five litres of water vapour. Finally, every home would benefit from use of a dehumidifier. Use it on the low, economy setting all the time, but turn it up when a higher moisture load is introduced into the house such as showering, cooking, or bringing damp washing into living areas. Ebac is a popular British-made brand with a good record, and they are offering a 20 per cent discount to Telegraph readers. Call 0845 634 1392 and quote the promotion code ASKJEFF. Incidentally, following my answer about external condensation on window glass, reader David Broome has suggested the use of a water-repellent coating such as Rain-X rain repellent, which is sold in motoring stores for use on car windows. I have no experience of this product myself, and would welcome readers experiences. Q. Further to your recent column on combi boilers, is it true that, at some time in the future, all replacement boilers will have to be combi boilers by law? Having taken in your views on the subject this is a rather alarming prospect. MS, by email
A. No, this is not true. All new and replacement boilers have to be condensing models, which are slightly more efficient because they extract some waste heat from the flue gasses (although any efficiency gains are probably cancelled-out by the short life expectancy of these boilers). However, there is no need for a new condensing boiler to be installed as part of a pressurised combi system, and there are no plans for this to become a requirement in the future. Condensing boilers work just as efficiently in a traditional indirect-pressure system, with a hot-water cylinder and cold-water storage cistern. For some reason, many readers confuse the two words, combi and condensing, and that confusion is exploited by unscrupulous heating engineers and firms in order to sell combi boiler systems, which are much easier for them to install, and therefore more profitable.

Q. Further to your recent discussions and solutions concerning heating and hot water, I have a further question. Two of my friends have had Megaflo systems installed. What is this and how does it compare with the combi and the traditional heating systems? SA, London A. Megaflo is one brand name for an unvented mains-pressure hot water cylinder. It works in much the same way as a conventional hot-water cylinder, being heated by the boiler, or by an electric immersion heater. The difference is that there is no cold-water cistern to provide indirect pressure to it. Instead you are dependent on the mains pressure, and if this is poor it can lead to the same problems experienced by owners of combi boiler systems namely poor water flow to upper storeys, and interference with the flow when two or more outlets in the house are being used at the same time. Unvented systems are generally not advisable unless you have good mains pressure (at least 1. 5 bar) entering the property via a 22mm supply pipe. The cylinder also requires a yearly test and maintenance by a service engineer. If your house has an existing hot-water system fed by a cold-water cistern, then I cannot see any advantage in removing this and replacing it with an unvented pressurised system. If the main aim is to get a powerful shower, then an electric shower pump is a cheaper and easier option. Send your questions to Jeff at Property, The Daily Telegraph, 111 Buckingham Palace Road, London SW1W 0DT, or email askjeff@telegraph. co. uk. Also visit Most likely insuffient ventilation as others have suggested. Life - breathing, cooking, showering - puts water into the air and without ventilation (deliberate or otherwise) the humidity climbs until it rains or condenses out no matter what the temperature. Raising the temperature does increase the amount of water the air can hold, and sometimes this is enough to compensate for a lack of ventilation, but there are limits. The dilema is that leaving windows open a crack increases heating bills.

That's the problem that heat recovery systems are intended to solve. They provide ventilation with reduced heat losses. We'd had problems in all three of the houses we'd owned. When we decided to self build we fitted a whole house vent system with heat recovery. Quite expensive to install but it does work very well. Perhaps too early for you to look at that though. I know the whole ventilation argument and how it relates to condensation. Like most people, I don't want to live in a draughty barn though, with windows half open all the time - so that's something we have to deal with. It's also daft to heat your house and then open the windows - on an ecological level and on an economical level. Our climate means we will always have moisture inside our houses and cold outside our houses and all the ventilation and extractor fans in the world are not going to fix that unless we just give up on walls and roofs and live in the fields. Condensation occurs when the warm moist air contacts a cooler surface and the 'air' is converted back into a liquid. The idea of double and triple etc glazing is that by insulating the bigs holes in the walls we call windows, the glass surface will not be cooler than the rest of the environment, and so will not encourage condensation to form. Obviously this does not affect the level of moisture present in the house - presumably if condensation is prevented from forming by the lack of a cool surface, the air will remain moist and we would probably all be more likely to get chest infections etc. It's clearly beyong the wit of the construction industry to develop a solution to this issue - (perhaps every house should have a condensation box - a cool area with a suction fan which draws the moist air towards it, and drains the resulting condensation outside). As I said though, leaving all of that aside - do people find new/modern double glazing an improvement on what they had before - specifically in relation to condensation forming and them having to wipe it up.

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