Gas Central Heating

[BertiWooster]

Am I correct in the following ?

1. The same water is circulated in the system

2. The radiator valve , increases / decreases the amount of water entering the radiator ; therefore increases / decreases the heat coming from the radiator .

[VHG]

>1. The same water is circulated in the system

Yes, but there is a small tank in the loft that will top it up if the water level drops (some water is always lost in the system)

>2. The radiator valve , increases / decreases the amount of water entering the radiator ; therefore increases / decreases the heat coming from the radiator .

Yes

[BertiWooster]

So , essentially the same water remains and is reheated and circulates through the system .
Therefore why are we told that turning down the radiator saves on energy costs .
Surely , what dertimines how much energy you use ( apart from the period the heating is on ) is the temperature that the boiler is set at to heat the water circulating in the system

( When you refer to the small tank - you are obviously not referring to a combination / condensing boiler )

[chas2008]

not quite correct- they are there to balance the water flow so all the rads heat up together, the amount of water going through doesnt alter the temp hence why TRVs are fitted to rads.
http://www.diydata.co...adiator_balancing.php

[chas2008]

the actual temp is controled by the boiler & TRVs, old fashioned boilers cant be altered but combi/condensing boilers can.

[chas2008]

Thermostatic Radiator Valves (TRVs) are often fitted to radiators to give a more responsive control of the radiator heat output according to the air temperature in the room. The head of the TRV has a sensor which responds to the air temperature around it. When the sensor expands on warming it pushes against a pin which closes the valve.

[BertiWooster]

What I am trying to understand is why turning the radiator down reduces the amount of gas used

[ChuckFickens]

Water return temperature.

if all the rads were turned off then the water would lose very little heat when pumped round the system so the boiler need to use less energy to get the water back to same temperature as when it left the boiler.

If the rads are all on full then a lot of the heat on the water is radiated into the rooms so the water returns to the boiler at a far lower temperature therefore the boiler need to put a lot more energy back into the water to get it back up to the same temperature gain.

[BertiWooster]

OK - so turning down the radiator reduces the amount of water that has to go through the radiator and therefore the water returns more quickly to the boiler and hence less time for it to cool down .

However , just as important in using less gas is at what temperature the boiler is set to heat the water to - yes ?

[chas2008]

yes, have your rads got TRVs ?... if so its a combination of both, if the boiler is set to low and the TRVs set high, the boiler will be on more often, trying to reach the higher temp...My inlaws in there 70s have just had c/heating for the 1st time and when i went there they had the boiler set at 55c the room stat at max and the TRVs at max, the boiler was on constantly as the house could never reach the temperatures that was asked for , the house was actually cold !!, i upped the boiler temp set the stat at 20/22 and and the TRVs at 50% , problem solved

[Landlord2010]

The first point to make here is, the volume of water inside the system is constant; it cannot be altered, unless you physically do something to it, such as, remove or increase the amount pipework or radiators.

Imagine the radiator valves as temperature controlled gates, in that they open and close, either partially or fully. If you set them at their highest they will generally remain fully open without restricting water flow. The lower the setting, it therefore follows that they will restrict the water flow sooner as they reach their set temperature. They do not increase or decrease the volume of water inside the radiator, they simply restrict its flow. Where water flow meets a closed valve it simply by-passes that radiator. The more valves that are closed simply means there is less free flowing water to heat, meaning that the boiler won't be on as long, meaning less gas used, meaning lower bills.

[BertiWooster]

At the risk of sounding dim here when you say ''.. they will restrict the water flow sooner as they reach their set temperature ...'' do you mean that the TRV itself is set to detect a set particular temperature of the water , according to the number it is turned to

[rojash]

"do you mean that the TRV itself is set to detect a set particular temperature of the water "
Yes. That's why its called a Thermostatic Radiator Valve :-)

[AlBags]

God sake Rogash .. That is WRONG.

A TRV controls the FLOW through the radiator by the use of a thermostat, which senses air (room) temperature.

If you're going to post, be sure you know what you're on about.

Lockshield valves on other end of the radiator can be damped down to "balance" the system ... Each rad will get a similar flow .. and the system is made more efficient, as there is the correct temperature drop across the rad when they are heating. That drop is approx 15-18degC

[BertiWooster]

Just to clarify then - for example if you turn the TRV from setting 7 to 2 , it will reduce the flow of water , untill it senses that the air temperature has reached whatever temperature setting 2 represents - is that correct ?

[ChuckFickens]

yes, though in your example changing from 7 to 2 would mean the valve would remain shut until the room got cold enough to open the valve, it would then open until the room temperature got above whatever setting 2 matches when it would shut again.

(AlBags, you post some good answers on here, but why act like such an elbow sometimes?)

[BertiWooster]

Thanks guys - I think i've got it now .