Energy lost through old patio doors

Prudent

I have a fairly well insulated house with a gas central heating system that was renewed about 3 years ago. Although most of the house has decent upvc double glazing, the patio doors are older (possibly 1990s or even late 1980s). They are double glazed but have aluminium frames. I have both blinds and heavy curtains at the patio doors which I close when it gets dark in winter. When I open the curtains and blinds in the morning it feels like their is a wall of cold air between the curtains and the patio doors. I am assuming they do not provide very good insulation. Is their heat loss likely to enough to make it worth considering replacing them?

Richie-from-the-Boro

20+ year old argon filled units should still be good, the cost of replacing with modern Low E windows is probably never going to give you much if any improvement in thermal transfer or the air leakage rate of the aluminium components of the fitted window. Assuming the doors are still functioning and no air leakage in the edge seal of the glass or glass to brick seal has developed over the intervening years I can't see any cost effective benefit in changing them. The fact that you feel a noticeable 'cold' when opening your blinds and heavy curtains at the patio doors tells me your blinds and heavy curtains at the patio doors themselves are providing an excellent additional service to you. If the opposite was the case, and you felt what you thought was a reassuringly warm and cosy temp when opening your blinds and heavy curtains [*-see below] at the patio doors I would immediately suspect the breakdown in efficiency of the glazed units, edge sealing and curtains.

* secondary glazing + insulated shutters 77%
* secondary glazing + heavy curtains 66%
* stand alone insulated shutters 60%
* double-glazing 55%
* honeycomb blinds 36%
* modern insulated roller blinds 22%

Prudent

Brilliant thank you Richie. I will save myself some money by just keeping the same doors then.