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[Finance] Is this the cheapest way of running central heating? Can't find an answer on the internet



A mex eyecan

Well-known member
Nov 3, 2011
3,253
I saved a FORTUNE in heating oil during last December’s cold snap by turning off the heating and toughing it out.

Imagine how I laughed when the house got so cold that the pipes in my loft froze then burst at 1am and flooded half the house and f***ed the electrics.

“Oh, you silly old sausage,” I thought to myself as the dining room ceiling collapsed.
That must have been dreadful.
 

Bodian

Well-known member
May 3, 2012
11,233
Cumbria
Correct but he’s saying he’s got a condensing boiler that isn’t a combi.
I have a condensing boiler that’s not a combi, it’s a system boiler. (Similar to a combi but connected to an unvented hot water cylinder)
Yes - but it's the 'condensing' bit that means the return temperature should be around 54 degrees. Whether that be a system, conventional, or combi condensing boiler. That is - it's not the fact that's it's not a combi that's key to what Bozza was saying.

But, like him, I don't understand how it really works. Much like I can't get my head round an air source heat pump using freezing cold air from outside to heat the house!
 

Bozza

You can change this
Helpful Moderator
Jul 4, 2003
55,239
Back in Sussex
Yes - but it's the 'condensing' bit that means the return temperature should be around 54 degrees. Whether that be a system, conventional, or combi condensing boiler. That is - it's not the fact that's it's not a combi that's key to what Bozza was saying.

But, like him, I don't understand how it really works. Much like I can't get my head round an air source heat pump using freezing cold air from outside to heat the house!
Sorry - I wasn't saying a combi boiler isn't a condensing boiler, just that my boiler isn't a combi boiler.

I've not done it properly yet, but with a little laser heat gun thing I've got and had a little play with, I can't see how the temperature coming out of the last radiator in my home's system is as cool as 54 degrees.
 

Nobby Cybergoat

Well-known member
Jul 19, 2021
6,465
Probably the single action I could take which would reduce my heating bills the most would be to file for divorce.

In the absence of that, yeh I suppose the one radiator trick
 

Rowdey

Well-known member
Jul 7, 2003
2,522
Herne Hill
If I turned off all the rads in my home except the one in the room I'm in - with the thermostat next to me - would this be the cheapest way to run central heating?

The internet has mixed views about this - what does NSC think?
No easy answer - How old is house, how leaky is it? (does it have cavity wall Insulation/Double glazing?) and what is boiler make/model? A larger size boiler (or worcesters in general..) can have a minimum fire of 5kw.. thats approx 5 rads worth of heat at it's lowest ignition point. If it's sending out 5kw to a rad less than 5kw output, the boiler will overheat, shut and restart ad infinitum (called cycling) and that is very inefficient.
Also, that one room you are heating, will be adjacent to cold rooms, and as we know, hot-> cold in all circumstances, so that (say) 1kw rad will now not only be trying to heat the room you are in, but the rooms next door too, so in fact you are not getting the full output of the rad in the room you want it..

I could go on (and on) but I keep at least two rads on to keep my boiler on the constant minimum fire, and also importantly keeps some warmth in the envelope of the house too.
 


Baldseagull

Well-known member
Jan 26, 2012
10,817
Crawley
I gave up on this question last winter due to the conflicting advice.

One view is to only heat the rooms you need to heat, turning off the radiators in the others. This logically makes sense to me since the water is still as warm as possible when it returns to the boiler, hence requires less energy to get it hot enough to send back around again.

But, for boilers like ours - a condensing (not combi) boiler - it seems that you want the water to be cool when it returns to the boiler, in order to facilitate condensing which is how the boiler works efficiently. I admit I have no idea how this works as it just seems completely illogical!
Set the operating temperature a bit lower if you are only heating one or two rooms, if its cooler going out it will be cooler still when it returns. The return water needs to be cool to extract heat from the flue gases, which is where the condensate comes from, the return water then goes into the main heat exchanger where it now requires less gas to heat it. as it has been warmed a bit already by the flue gases.
Any heat lost from the water is lost into the house, which is what you are trying to heat. Any heat lost out the flue is wasted, so having the return water cool means it has dumped its heat into the house and is now better able to recover heat from the flue gases and prevent that being wasted to outside.
 

beorhthelm

A. Virgo, Football Genius
Jul 21, 2003
35,179
Set the operating temperature a bit lower if you are only heating one or two rooms, if its cooler going out it will be cooler still when it returns. The return water needs to be cool to extract heat from the flue gases, which is where the condensate comes from, the return water then goes into the main heat exchanger where it now requires less gas to heat it. as it has been warmed a bit already by the flue gases.
Any heat lost from the water is lost into the house, which is what you are trying to heat. Any heat lost out the flue is wasted, so having the return water cool means it has dumped its heat into the house and is now better able to recover heat from the flue gases and prevent that being wasted to outside.
this seems like overstating the efficencies gained from condensing. you dont *need* the return water to be cool, its just more efficient for normal operations compared to not using the exhaust heat. if you want water at 60deg and returns at 50deg, its still less energy than if it returns at 40deg.
 

Baldseagull

Well-known member
Jan 26, 2012
10,817
Crawley
this seems like overstating the efficencies gained from condensing. you dont *need* the return water to be cool, its just more efficient for normal operations compared to not using the exhaust heat. if you want water at 60deg and returns at 50deg, its still less energy than if it returns at 40deg.
You do *need* the return water to be cool, (below 55 degrees max) to extract heat from the flue gases, which is what I said. You dont *need* a condensing boiler at all, but if you have one, you might as well use that function and save a bit of gas.
Not sure what you are trying to say with your example, but if you have an operating temperature of 60 degrees and it returns at 40 degrees you have taken that 20 degrees of heat from the water into your home, and the 40 degree water will gain more heat from the flue gases than if it was returning at 50 degrees.
In an ideal but not achievable system, you would extract all the heat above your target temperature for the house/room from the water just before it is returned to the boiler. Yes, it will need less energy to heat the water from 50 to 60 than from 40 to 60, but the water is just a transport mechanism for the heat to get into your rooms, the heat it loses is the heat your rooms gain.
 


BrightonCottager

Well-known member
Sep 30, 2013
2,045
Brighton
You do *need* the return water to be cool, (below 55 degrees max) to extract heat from the flue gases, which is what I said. You dont *need* a condensing boiler at all, but if you have one, you might as well use that function and save a bit of gas.
Not sure what you are trying to say with your example, but if you have an operating temperature of 60 degrees and it returns at 40 degrees you have taken that 20 degrees of heat from the water into your home, and the 40 degree water will gain more heat from the flue gases than if it was returning at 50 degrees.
In an ideal but not achievable system, you would extract all the heat above your target temperature for the house/room from the water just before it is returned to the boiler. Yes, it will need less energy to heat the water from 50 to 60 than from 40 to 60, but the water is just a transport mechanism for the heat to get into your rooms, the heat it loses is the heat your rooms gain.
I think I understand the logic behind this, but most of the copper pipework between the rads is in walls / under floorboards so the heat 'lost' is transferred to those walls and those cavities, rather than the rooms, isn't it?
 

Baldseagull

Well-known member
Jan 26, 2012
10,817
Crawley
I think I understand the logic behind this, but most of the copper pipework between the rads is in walls / under floorboards so the heat 'lost' is transferred to those walls and those cavities, rather than the rooms, isn't it?
If the pipework is under floor, that heat will rise into the rooms eventually, if it is in stud walls might be losing a bit there that doesnt benefit you, but if the cavity is small it will warm up quite quickly and not so much heat will be lost there once it is warm. Most of the heat should leave the system through the radiators, if you are only using one or two then it is probably worth dropping the operating temperature, this is no problem with a combi, but potentially a problem with other set ups.
Most advice is to keep a system that also heats hot water in a storage tank above 65 degrees operating temperature, and set the stat on the hot water tank to 60 degrees, to prevent legionella bacteria growth, I am not going to advise you differently, but if you understand where and how you could have problems, you don't need to always have hot water at this temperature.
 


Justice

Dangerous Idiot
Jun 21, 2012
17,907
Born In Shoreham
I have insulated to the max on the inside of all outside walls plasterboard backed with kingspan. It really does make a huge difference to heating bills. We’ve just done a project in super quilt which is cheaper and meant to be more efficient although you need to batton out the walls quilt then plasterboard.
 

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