Does this seem a fair glazing quote and are these u-values correct?

[lardconcepts]

Living off the mains gas grid, heating with LPG is expensive. Twice the price, if I've read this table correctly:

've done all we can with insulation, but the current double glazing on the windows is old and incredibly thin (4mm or something).Last winter, the snow remained on the roof all the way through until the melt, but the velux windows were melted off in about an hour!

We had a quote from a local manufacturer, and actually, it's not as bad as I thought it would be. This is for replacing the glass into the current, sound, traditionally shaped wood frames, including curves at the tops (so glass needs to be shaped) I've turned his paper "pick and mix" quote and u-values into a spreadsheet for my own info - does all this look right?

particular, note the decreases in u-values regarding the filler gas vs the increase in price. Is it actually worth going for Krypton?

We're hoping to get a fair bit of passive solar gain through the south facing patio doors and windows.

The company come well recommended locally and by neighbours, and to be honest, the bloke doing the quote was so pleasant and un-pushy, if you think this looks fair I don't think I'll even bother with a second quote. The last time I got a glazing quote at my old house, it was a thoroughly unpleasant and pushy experience and came to a stupidly high price so I didn't bother.

Anyway, whaddya reckon? Do my sums make sense? Googling around here and elsewhere seems to show that having a gas fill is definitely noticeably worth it, but would you bother with the krypton?

Thank you.

[Tabby]

Gas fills are used to improve the u values when new, what they don't mention is the gas then leaks out, and performance deteriorates. You'd get the same gain when new by adding a secondary glazing pane to your existing dg, the 2 differences are that the insulation gain would be permanent rather than temporary, and it would cost less. If you added a clear plastic film on the window side of this new glass pane, spaced off it, you'd have quadruple glazing, with even better gain.

NT

[John Rumm]

> We've done all we can with insulation, but the current double glazing

numbers look plausible. If you compare to some of the figures shown here:

E glass and argon fill seem comparable... Krypton looks like its better still.

Its a payback trade off question really. If you assume the average temperature differential across the window is 10 degrees. You have not specified the total window area, but for the sake of argument, lets say it amounts to 20m^2 for all of them. The difference between u values of

2.1 and 1.4 would translate into difference in rate of heat loss of 2.1 x 20 x 10 - 1.4 x 20 x 10 = 140W, or energy loss of 3.36kw/h per day. So at 8.45p per kw/h that amounts to 28p/day. If you are paying that for 120 days a year, then about £33/year. That would mean a 20 year payback (ignoring loss of interest on the money or cost of borrowing - whichever is appropriate) on the extra cost moving from air to krypton (assuming the units stay sealed for that long). Although you can factor in a better comfort level with the better u Values.

Most of the solar gain is via radiation, so the reduced conduction losses that the gas change brings. Have minimal effect on this. However the use of Low E glass (as is common these days) will reduce transmissive gains a little. It also reduces light transmission a little, which may mean needing more energy input from lighting for some of the year.

Argon would give you a 60W reduction in losses based on the above numbers. So the payback sums are cost neutral really.

Might be worth doing some more detailed estimates of window area. Also ask the supplier what the life expectancy of the krypton filled units are.

[lardconcepts]

etc. Wow - I'm incredibly impressed at this answer. Wish I could rate it! That's really given me something to chew on, some questions to ask of the company... oh, and thanks for the DIY FAQ link too (now bookmarked).

(It's good to see pe> Gas fills are used to improve the u values when new, what they don't

Hi Tabby,

a good thought, but due to the shape of the existing windows, secondary glazing has been ruled out as awkward. Plus the fact that a fair few of the original units are leaky and clouded up means it's probably time to make the change. But the plastic film idea sounds interesting, must look into (or through!) that.

[John Williamson]

Do the calculations, and you'll find out *why* it's discouraged.

I was over at the Centre For Alternative Technology a while back, admiring their 10Kw PV roof. So I plugged in some optimistic figures and came up with about 50p/ KwH, if I ignored the cost of running the battery bank they use it to keep charged, and assumed mortgage interest rates over a 25 year life.

[Tabby]

Plastic film has limited life, but is exceptionally cheap and easy to fit, and on secondary glazing is well protected. Payback is good as long as its not trapping water on wood, leading to rot. Do you want to post pics of one or more of your windows, as there arent many that cant be secondaried one way or another.

Clouded units: fwiw some people have managed to drill them to clear them. If you're due to dispose of them anyway, there's little to lose. Drilled dg works fine afterwards, and your new ones will also mist up at some point in time, so its not as if new ones are a permanent fix.

NT

[Tabby]

This, and perhaps more later, would make a great wiki article

NT

[The Natural Philosopher]

In all cases heavy interlined curtains can up to halve the heatloss when drawn closed.Not cheap, but they look good! the better the draught seal the better they work.

There was a reasons for all those tapestries on stone castle walls you know!

[Terry Fields]

For our metal-framed patio door, SWMBO made up some curtains with triple linings, including one 'thermal' lining. With draught excluders at the bottom and taking care to arrange it so there were no gaps, most of the temperature drop was across the curtains!

If the OP has windows with a proper cill, put a draught excluder in place every time they are drawn, that can make a big difference too. Ditto draught excluders on the internal doors. Find where any draughts are coming from and stop them.

Cold spots in rooms can be evened out by placing a small fan under a radiator running on slow speed - it makes a real difference to the comfort level and may mean the room stat could be turned down.

TF

[lardconcepts]

Replying to several posts and comments at once here, but starting with Tabby's pic request:

Here's how thin the patio door currently is:

here's how foggy the fogged up old glazing with 5mm gaps which makes up most of the rest of the windows are. making the first post, I found a couple of things out, the first of which has made me have a major rethink about the whole thing. The guarantee on the sealed units, ie, the double glazing that goes inside my frames, is 1 year. Which is about 9 years less than I was expecting! I'll probably get the worst two units done.

Also, I asked about Kyrpton vs Argon, and also Planitherm, which was mentioned but not quoted for. When I googled it, it seems that Planitherm is actually better than Pikington K.

The reply from the company is: "The thing to remember is Krypton is more efficient the narrower the airspace where as argon works the opposite way. We can do planitherm which is the same price".

So should I forget about the Pilkington and go for the Planitherm?

One thing I maybe should mention is that it gets cold where we are in Wales. Very, very cold. Like, -16c last winter. And for 3 days running, the accurate, well-placed outdoor thermometer never registered a daytime high of less than -6c for 3 days running. So, factoring LPG too (twice the price), every therm/kW counts!

[John Rumm]

Makes one wary of spending too much on exotic gas fills.

Not sure that makes much sense - it would suggest a negative u value!

If you repeat the sums I did with more accurate area measurements, you could perhaps allow a higher temperature differential for some parts of the year as well. Slap the figures in a spreadsheet and see how they work out.

Moving from single glazing to double will represent a large improvement

- probably halve the loss of heat directly through the windows, and possibly also make a big impact on that lost though drafts. However going from correctly functioning DG to "better DG" is far far less of a gain - unlikely to be more than a 25% improvement. Much depends really on how good the rest of the house is, as to where this represents the most return you can get for the expense.

[Tabby]

Seems to me the whole gas thing is just another game. Coatings are good in principle, but not really worth t in practice when you can go to triple glazing for less cost. Glass is cheap, and not many windows have no way to put openable secondary glazing on. And that doesnt lose its value.

NT

[dennis]

You can always fit some shutters, they can have insulating values several times what glass has. Even curtains can have better insulting values than glass so fit liners and curtains before wasting money on argon, etc.

[lardconcepts]

I th> > Here's how thin the patio door currently is:

> I'm not seeing a problem there

The gap is 3-4mm, WAY too small, no?

Hmm, but they're windows. For letting light in and looking out of. Good heavy curtains are drawn at night anyway, it's really the day we need to reduce the losses.

[Tabby]

It sure doesnt look that small in the pic, but even if it is I dont see any justification for replacing teh healthy ones. DG replacement just isnt worth the cost on energy saving grounds.

day and night really.

NT

[lardconcepts]

Now here's a thing - I went to the factory today. It's not big, and I could= see all corners of it and units at all stages. I couldn't see any gas tanks or any sort of facility for "gassing up" units= . Is it possible they order them in from someone else? Or send them off to = be filled? Or is it possible that, as no-one will ever know what's in them,= people just quote for a gas and fill them with air?

[dennis]

Do they make the actual glazing units there or just the frames?

[Man at B&Q]

ld see all corners of it and units at all stages.

ts. Is it possible they order them in from someone else? Or send them off t= o be filled? Or is it possible that, as no-one will ever know what's in the= m, people just quote for a gas and fill them with air?

They probably just put together the frames. The glazed units will be bought in.

MBQ

[lardconcepts]

Nah, that's what I'm saying - it's the GLASS they do there. I saw single sheets in one corner, work in progress is another, and a couple of blokes adding some sort of black seal to the edge of a unit.

Of course, there's always the possibility that they get them gassed elsewhere, or the gassed ones are made elsewhere, but if you can never tell what's in them, then who's to say it's not air?