How much heat loss through relativly new DG windows.

[Donwill]

I'm trying to get an approximate heat loss value for 2 patio doors and one window which face into an unheated DG conservatory. I have made overnight observations over about a year on outside temp and conservatory temperature The conservatory being between 10 and 6 deg C warmer than outside. The 10 deg diff tends to occur on very cold nights which are still and clear ( radiation frosts), the 6 deg diff during windy warmer nights. Disregarding the positive effects of no wind ( boundary layers) on the house patio doors and window, what is the approximate heat loss from house to conservatory through 12.6 Sq M of DG per Deg C.

Don

[dom]

To calculate the U-value you either need to know the thermal heat capacity of the room (difficult), or the power required to maintain equilibrium - i.e. how many watts of fan heater would be required to maintain the room at a constant temperature.

For instance, if the floor of the room was of heavy concrete construction (and well insulated from the ground), this would slowly give up heat to maintain the room temperature. But if the floor was of light timber construction it would be far less able to release stored heat to hold up the room temperature - i.e.they have very different thermal heat capacities.

You also need to know the losses through the other walls of the room - and even this neglects losses due to air leakage.

[The Natural Philosopher]

IIRC U value about 3 -5 for DG,2-3 for TG the difference tending to be to do with what they are filled with and the frame.

[The Natural Philosopher]

the glass, the air gap and whats in it, and the type of weather ouside, and the conductivity of the frame. And the dimensions of all of it.

[dom]

Bit high. Mine are 1.8 to 2.0U for double glazed 4/16/4 (glass/air/ glass) and low-E coating.

[The Natural Philosopher]

So about the same as a 2" oak door.

Or single glazing plus lined curtains, then :-)

[John Rumm]

See the DG window table here:

a number appropriate for your DG - lets say it was 2.6 then you simply multiply that by the total area and by the temperature difference. You get an answer in Watts.

[Man at B&Q]

Why bother? You look up the U-value in an appropriate table and do the calculation from there using the temperature difference. He did say an approximation.

MBQ

[Donwill]

Many thanks for all the replies Cheers Don