Turning radiators off

[bumbledeedum]

So I've googled and I still don't understand... I keep seeing people say they're running their heating for hours every day but have turned most their radiators off so only heating 2 or 3 etc so it shouldn't cost as much. How does this save any money/gas? Surely if the boiler is on, it's on and using gas so you might as well have all the radiators on?

I've got to be missing something here?

There isn't as much water flowing round the system to heat up so it uses less gas.

So the boiler isn't just on or off? It uses different amounts of gas?

Yes, the boiler pumps water round the radiators when heating is on but only heats the water when the return flow temperature is below a certain temperature. This might be constant if the house is very cold or sporadic if the house is warm.

If you turn lots of radiators off then the water won't have dropped as much in temperature when it gets back to the boiler so will use less gas getting it back up to temp to be sent round the system again.

Yes it's more like a car than a light bulb, it doesn't just use a certain amount every minute you drive, it varies based on speed, gear, hill, wind.
In fact the most efficient way for a boiler is to have it on all the time with the water temperature as cool as possible.
A bit like driving 100 miles at 50mph you'll be driving for a lot longer time than at 80mph, but you'll save petrol overall.

In fact the most efficient way for a boiler is to have it on all the time with the water temperature as cool as possible.*

Is that with a combi-boiler too?*

Whether having your heating on low all the time is the most economical thing will depend on many factors from the type of boiler you have and how your control your heating ie trv’s smart etc to how well insulated your house is. Insulation is always going to be the first place to make savings on your heating bills.

Yes it's for any condensing boiler. It's more tricky with a non combi as you would need a weather compensating controller, otherwise the cylinder would not charge.

Sorry good point I worded that really misleadingly.
I meant only when there's demand, not 24h a day.
So instead of ticking on and off with the thermostat, the boiler would be only just keeping the room up to temperature and the radiators would be lukewarm except in mid winter.

A way to think about it;

Radiators heat rooms by transferring the heat from the boiler (in the form of hot water) to the room. To keep heating the room the water has to be repeatedly reheated and pumped round. The more radiators that are transferring heat into rooms, the more water the boiler has to keep heating and pumping.

Great big houses with terrible insulation have bigger gas bills than tiny well insulated flats even though both have the boiler turned on because the boiler has so much less water to heat, and in badly insulated rooms the heat goes out through the walls and the radiator has to keep reheating it.

By turning off radiators in an unused room, and shutting the door, your boiler is having to heat less water to heat that room.