Gas Boiler: Using all/some radiators?

maxsaver_2

This question has been bugging me for ages! Does having the valves on all radiators in the house 'open' (so every one gets hot) use more gas than just having a few of them on?

I thought that with a gas boiler, when it's on, it's always going at 100% so it won't make a difference. When using, say, half the radiators, they might get hotter than using them all but it'll use the same amount of gas. Is this right?

Possetjohn

This question has been bugging me for ages! Does having the valves on all radiators in the house 'open' (so every one gets hot) use more gas than just having a few of them on?

Answer is yes. Once the system reaches temperature an old boiler will cycle (burner on/off) and a modern boiler will modulate the burner using less gas. More radiators on =more demand hence more gas burnt. Of course some heat will escape to the unheated rooms increasing the demand. Better to have thermostatic valves on the radiators.

I thought that with a gas boiler, when it's on, it's always going at 100% so it won't make a difference. When using, say, half the radiators, they might get hotter than using them all but it'll use the same amount of gas. Is this right?

Answer is no

With an old boiler the burner is either off and on. The burner runs until the boiler heat exhanger thermostat temperature is reached, then the burner goes off. With these old thermostats the temperature of the water at the top of the heat exchanger needs to drop 10-15°C until the boiler refires. The amount of gas used depends on the total burner on time plus the pilot light consumption.

Modern condensing boilers with fans have modulating burners and electronic control systems and run to an adjustable set CH water output temperature. The amount of gas burnt is therefore pretty similar to the heat demand from the system as these boilers are 85 to 90% efficient.

Hope this helps

Cardew

maxsaver wrote: »

This question has been bugging me for ages! Does having the valves on all radiators in the house 'open' (so every one gets hot) use more gas than just having a few of them on?

I thought that with a gas boiler, when it's on, it's always going at 100% so it won't make a difference. When using, say, half the radiators, they might get hotter than using them all but it'll use the same amount of gas. Is this right?

The post above is absolutely correct.

The simple way to look at it is - the more heat you produce, the more gas you use.

Take a extreme case. If you were heating Buckingham Palace and had one radiator on, or all 1,328 radiators on(I haven't counted them recently:cool:) - which do you think would use the most gas?

albyota

can I answer that sir?

1,328:j

maxsaver_2

Thanks for clearing that up. Good to know. :cool: