Patio Doors between Living Room and Conservatory

We have Patio Doors between our constantly used livingroom and Conservatory. We leave the radiators on in the 2 locations at approx 20 for a number of hours each day. Does anyone know how to assess the cost effectiveness between (1) closing the doors and only turning on the rads in the conservatory when it is actually in use by which time the conservatory could be very cold (2) and leaving the doors open and leaving the conservatory rads on as per the living room.

The livingroom radiators alone would not be sufficient to heat the conservatory and vice versa.

I know it must cost more, but how much more. I've heard it said that some gas fitters say that there is very little different in cost between turning rads on and off room by room. How much are we paying for such a luxury. If we close the doors the conservatory gets quite cold whereas when we leave the doors open and rads on the heat from the conservatory seems to support the livingroom heat.

Hope this query is not too confuddling.

Comments appreciated please.

Conservatories that face south can make a contribution to the energy efficiency of a house by collecting heat on sunny days, the heat can then be shared with the rest of the house by opening the door to the house. When its overcast the door should be kept shut and if possible some form of insulating blind drawn over the conservatory. The conservatory then acts as an insulating layer to the house reducing heat loss through the part of the outside of the house which it covers. Heating a conservatory, from an energy efficiency perspective makes absolutely no sense. Even if you have very low u value glass you are still more or less heating the garden.

If you are heating with gas why don't you try your senarios for a few days each, taking meter readings on the gas usage. You would need to have similar weather conditions, if the conservatory faces south a bit of sun can make a huge difference. Also compare your gas bills with your neighbours without conservatories. Heating the conservatory may cost you a lot but it might be much cheaper than a proper extension or a bigger house.

We tend to use our conservatory all the year round - that was our intention when having same constructed. I believe that natural day light is good for the spirit so on overcast days I find myself gravitating towards the conservatory because it is then the brightest room in the house. We have so many "overcast" days I believe that to keep the door closed and the blind drawn would defeat the purpose. I have never seen insulating blinds in conservatories. Perhaps these would be useful overnight. I appreciate that heating a conservatory isn't the most efficient way of using my gas heating, but I don't agree that we are still more or less heating the garden. I can sit in the heated conservatory but I certainly couldn't sit in my garden at this time of the year.
I must see if I can get a key or whatever to unlock the gas meter which is on the outside of my house in order to keep a tab on usage over a few days. The conservatory faces East. Thanks for your response.