Cental heating on all day (Again).

[David.WE.Roberts]

An article in the Telegraph I came across by chance.

Has a pop at the Energy Saving Trust.

Suggests "Hence my advice that in cold weather, rather than run your central heating for two hours in the morning and six in the evening, it is better to keep it on the ?24 hour? setting, but running at a low boiler temperature. Turn all your thermostatic radiator valves to the highest number, or ?max?, and turn the boiler thermostat down to one, or ?min?. The room thermostat can be at whatever temperature you find comfortable ? I?d suggest 19C (66F) or 20C (68F) during the day, and down to 16C (61F) at night, but you can make your own choices. This advice is offered for its guiding principles, not as rigid instructions. "

Haven't seen this suggested before in the various debates.

So is it better to run a modern condensing boiler continuously at the lowest temperature setting instead for shorter periods at a higher setting?

At first read through the suggestion above seems to be a load of b*llocks.

For instance, why tinker with the radiator thermostats? I don't see how this 'advice' has anything to do with setting a maximum temperature for an individual room.

The implication seems to be that some rooms will be heated above the normal chosen level and this will have some benefit. Does not compute.

The article does make the good point that maintaining a minimum temperature at all times is a good idea to help prevent condensation in the walls reducing thermal efficiency.

At the moment we run the whole house thermostat (portable wireless programmer) at 21C from 06:00 to 08:00, 19C for the rest of the day and

16C over night.

Time will show if this is efficient.

Cheers

Dave R

[Dave Plowman (News)]

A decent modern condensing boiler modulates the burner and therefore output with no loss of efficiency. An older one which simply switches the gas on/off is a different matter.

[Andy Burns]

It will depend on the age/efficiency/type of boiler/thermostats/insulation/draft proofing of the house.

It might work out in some cases, but since you can't reproduce a given day as a control experiment, how will you ever know?

[stuart noble]

I think this is where the HDD figures come into their own

[John Rumm]

He has a habbit of writing stuff that is in many cases quite sound, but often romps off on flights of fancy...

Yes. Condensing efficiency rises with lower return temperatures (it allows you to extract more heat from the combustion process and the flue gasses end up cooler). Also there is a slight improvement in the *rate* of efficiency gain (i.e. the curve gets steeper) at the dew point of the flue gasses as well (about 54 deg C IIRC). Just enough temperature also reduces cycling.

Its a mixture of sound theory, old wives tales, crap, and guesswork! So in most cases it may not be right, but its probably not even wrong either.

Without much more detail on the type of boiler fitted for example its hard to make a sensible comment. For example an old cast iron lump will also gain efficiency if you drop the flow temp enough so that the boiler starts to condense. However it will also shag the boiler in fairly short order since their combustion chambers are not designed to be routinely filled with water. So the best flow temperature there is "just enough" to prevent condensing and promote longer burns with less cycling. Assuming its enough to actually get the house up to the required temperature.

With some older larger properties, they may have a huge thermal mass, and the reheat time may be measured in days rather than minutes. In these cases maintaining a minimum background temp not too far below the "normal" comfort one will be the only way of getting to the comfort temperature in a sensible time frame. (I was speaking to a chap who is on the technical services team for a local church that's a substantial brick and stone building from the 1800's. He said they found that it was pointless having a room stat as such, since the time constant for the building was so huge. Instead they use a weather compensation system and the heating is on pretty much all the time, but driven from the external temperature such that the heating input follows the trend set by the outside temperature instead)

I expect that bit falls into the aforementioned "crap" designation.

Indeed.

Yes, although it ignores the timescale... Installing central heating in any house will lower the normal humidity over time, and I suspect it does not really matter what duty cycle you run so long as the whole place spends a few hours a day at "comfort" temperature.

Its seems unlikely that you will get dramatic swings in humidity deep in the fabric of the building in response to short term changes - they are likely to follow long term averages.

There is certainly scope for making improvements, but as with so many things like this the real situation is a complicated mix of interactions and conflicting requirements.

[tim.....]

I can't work out whether that's a vote for keeping it on all day, or not

(and I'm soon to have an interest in this answer)

tim

[David.WE.Roberts]

I think that was a vote for not turning the temperature knob down because the boiler works out the most efficient way to provide the heat.

I think.

[Dave Plowman (News)]

No point if you and yours are out all day. Just experiment with on times so the house is up to temp for when you come home.

When I'm at home all day, I tend to run at a lower temp during the day when I'm doing things than in the evening when I'm lolling on the sofa watching TV. ;-)

[tim.....]

How can it do that unless it also knows whether you want the house to be warm 24/7 or for 4 times 1 hour a day?

Or does it also read the timer to do this?

tim

[tim.....]

but this is (often) not the case.

Obviously, I can experiment with what makes the house most comfortable but what I can't easily experiment with is what makes the boiler burn most efficiently (and ultimately what makes the boiler less prone to breaking).

I.e is is better for the boiler to run at 60 degrees for one hour and then off for one hour, one for one hour...

or

run at 40 degrees constantly?

I really have no idea.

tim

[Dave Plowman (News)]

A decent boiler will decide for itself. Weather compensation can help it compute things.

[ARW]

Just get a wife. She will turn the boiler on full and open the windows if the house gets too warm.

[Owain]

And leave the cooker gas on unlit if she's aiming for that 'open-plan' look

Owain

[John Rumm]

With a modern boiler, then the ideal rate would be the one that matches the heat loss rate of the building, so if the building is losing heat at a rate of 5kW then that is what it sticks it back at. Many modulating boilers won't be able to go that low, so they will cycle a bit.

[Onetap]

More Howellers from Jeff. This article was discussed on this forum some wee ks ago.

Yes. For example, it's more efficient on a multiple boiler installation to run all the condensing boilers at a low output, rather than one boiler at a high percentage of it's output. ISTR that the efficiency is fairly uniform for various outputs, once it is operating in the condensing zone.

Except for the better point that it's bollocks. He derides the EST for havi ng no research to back up their recommendations, but he seems to have pluck ed this idea from nowhere. I've never heard it elsewhere. Can he provide an y references to support this theory?

[Onetap]

operating in the condensing zone.

No, correction to that, the efficiency increases slightly at lower outputs. There's a significant step/rise in efficiency below the dew point.

I recalled the shape of the graph accurately, but for some reason my memory ahd switched the axes around.

There are numerous graphs on the internet, all showing much the same thing, if you search Google images for 'condensing boiler efficiency temperature'

For example,

[David.WE.Roberts]

Interesting stuff.

One implication is that you need a large radiant area such as UFH to get the best efficiency out of the boiler.

Cheers

Dave R

[Dave Plowman (News)]

Indeed. Rads ok for an old system where the temperature was about 90C may well be too small for a condensing boiler running at maximum efficiency.

[David.WE.Roberts]

Too late for us now, but this suggests that for a new installation the boiler efficiency is better if you put in over size radiators and run the whole system at a lower temperature.

Although how long it will take to recover the extra cost is another matter.

Cheers

Dave R

[Andy Champ]

I think I'd say that when installing put in the biggest rads you can, the extra cost of the bigger rad is probably small compared with the install cost of the system.

On the other hand the benefit to be gained by replacing old small rads with new big ones is probably nor worth the trouble. Just as with replacing old boilers or old windows.

Andy