Heat one room only, using gas combi boiler. Wasteful?

Yorkshire_Pud

Currently trying this to save energy costs, other radiators all turned off. All have their own thermostatic radiator valve TRV.

My query is does the boiler send heated water to each of the other eight turned off at TRV radiators which doesn’t go through the radiator but does the heated water actually reach the pipe work on the end of the radiator thus potentially wasting gas to heat water that just sits in the pipe work around the home?

Or are all radiators on their own mini circuits off a main pipe and simply don’t get sent/receive  any hot water unless the thermostat is turned up on that particular radiator? Therefore no gas is wasted?

The_Fat_Controller

If the valve is shut there cannot be any flow, no water can reach that closed valve.

You are overthinking things.

There must be some flow in the hidden pipework that is feeding any radiator where the TRV is open, but the waste will be negligible.

Xbigman

A bigger issue is that the boiler isn't designed to work that way. Having just one radiator on is like driving a car everywhere in first gear. It will only cost a tiny bit more to run one radiator on full and the others on minimum and it will be more efficient.


Darren

Yorkshire_Pud

Xbigman said:

A bigger issue is that the boiler isn't designed to work that way. Having just one radiator on is like driving a car everywhere in first gear. It will only cost a tiny bit more to run one radiator on full and the others on minimum and it will be more efficient.


Darren

That’s why I was wondering if it would be better to just use the gas boiler for hot water until it gets really cold weather and use an up to 2kwh electric oil filled radiator in the one room until then!?

ariarnia

any waste will probably depend on your system (and how big it is) and the size and insulation of the room you are trying to heat with your electric radiator but as electric costs three times as much as gas then its probably cheaper to heat the room with the gas radiator unless you have a massive house with miles between the room and boiler and exposed pipes. 

if you already own the oil filled rad and have smart meters then maybe do a quick (not very accurate) test by having your central heating on one day and using the radiator the next? if the 2 days are about the same temp and weather outside and everything else stays consistent then it should give you some idea. 

QrizB

ariarnia said:

any waste will probably depend on your system ... but as electric costs three times as much as gas then its probably cheaper to heat the room with the gas radiator

I agree with this, even allowing for the (potentially) lower efficiency the gas heated system is almost certain to cost less.

Yorkshire_Pud said:

That’s why I was wondering if it would be better to just use the gas boiler for hot water

Are your heating tes the same as your water heating times, or different?

If you're running the boiler for hot water, heating a radiator at the same time won't significantly affect the efficiency.

Yorkshire_Pud

ariarnia said:

any waste will probably depend on your system (and how big it is) and the size and insulation of the room you are trying to heat with your electric radiator but as electric costs three times as much as gas then its probably cheaper to heat the room with the gas radiator unless you have a massive house with miles between the room and boiler and exposed pipes. 

if you already own the oil filled rad and have smart meters then maybe do a quick (not very accurate) test by having your central heating on one day and using the radiator the next? if the 2 days are about the same temp and weather outside and everything else stays consistent then it should give you some idea. 

Already have the electric rad and a separate plug in energy meter. Need an extension lead first. The electric rad seems to send heat straight up to warm the ceiling and not convect heat so much sideways. Gas costing about £1.30 a day currently nearly all for CH on for about four or five hours. So equivalent to about four hours x 1kw of electric rad. If go up to 2kw setting double cost of gas. So far think the gas gives better more even heat. Reason for choosing one over the other is I’ve read reports that state it’s bad for the boiler efficiency if only one radiator is on but then I’m not going to leave all 9 on for that theory!? Same principal as leaving a car engine running 24/7 so it’s always warmed up, widely debunked and I think  the same for using one rad. (but so many people have different opinions) not to mention leaving the hearing on all night, I never do that.

Yorkshire_Pud

QrizB said:

ariarnia said:

any waste will probably depend on your system ... but as electric costs three times as much as gas then its probably cheaper to heat the room with the gas radiator

I agree with this, even allowing for the (potentially) lower efficiency the gas heated system is almost certain to cost less.

Yorkshire_Pud said:

That’s why I was wondering if it would be better to just use the gas boiler for hot water

Are your heating tes the same as your water heating times, or different?

If you're running the boiler for hot water, heating a radiator at the same time won't significantly affect the efficiency.

I don’t use much hot water and no set time just as and when throughout a day, heating an hour in the morning and three or four hours evening during which I may do washing up and hand washing a few times. Just wondering if the boiler likes only heating one radiator but I suspect it doesn’t harm it nor cost more in gas overall as the time off reduces any additional start stop operation.

chris_n

Just be careful running a 2kW load for an extended period of time through a plug, especially so with an extension. Plugs can start to warm up especially if anything is at all loose, especially fuse holders. Usually heating appliance manufacturers say not to use an extension.
I'm sure it's not a problem if you use good equipment and check regularly for signs of anything getting hot. Just something to bear in mind.

ariarnia

i was actually wondering about efficiency with condensing boilers if only one rad is on. does that mean you have to be more careful about flow temps as maybe the water wont lose enough heat before getting back to the boiler to condense properly? i remember reading somewhere there had to be at least 10 degrees of difference between the in and out flow for the 90 plus % efficiency to happen. 

QrizB

ariarnia said:

i remember reading somewhere there had to be at least 10 degrees of difference between the in and out flow for the 90 plus % efficiency to happen. 

That's folklore, not fact. Whether the boiler condenses properly or not is really down to the return temperature being cold enough. It doesn't matter whether it's going out at 70C and coming back at 50C, or going out at 52C and coming back at 50C.

i was actually wondering about efficiency with condensing boilers if only one rad is on.

The issue is that one radiator might only be able to dissipate (say) 1Kw, while your boiler might only be able to modulate down to (say) 5kW. This means that the boiler will cycle on and off, being on only 20% of the time. Cycling reduces efficiency for various reasons (including the purge air that is blown through your combustion chamber with each cycle).