Gas central heating

[alfie jones]

My gas central heating system has 3 settings:  heat the water only, run the radiators only, or both together.  Would the system use more gas to do both (water & radiators)?  If so, and very approximately, how much extra gas would be used? 

It sounds a simple question but I've never been able to get a straight answer.  Thanks very much. 

[Impret-Sir]

I would say that the system would use more gas to do both, as the water will cool faster if it is "radiating" heat into the house from the radiators, (as they are designed to do,after all) so the thrmostat will cut in more frequently to heat the water back up again. It is impossible to guess how much more gas you would use, that would depend on how high you set the radiators, and how cold the weather, and therefore your house, were at the time.