Worth getting boiler with external temperature compensation?

[men8ifr]

I'm looking to replace my 20year old heating/water system with a combi and wondered if the external temperature compensation is worth getting in terms of comfort/performance or energy (cash) saving?

IIRC it's the veissman that has it and they say it's worth 2% on the SAP rating but I can't find out if teh rating given (approx 90%) includes this 2% or not so maybe I bought this boiler and didn't have the feature/sensor/add-on the performance is actually 2% worse than many other boilers I'm looking at.

It seems like a good idea anyway - does it help heat the house faster? Keep a better temperature?

 

[45yearsagasman]

You've just opened a can of worms by asking that question.WC has been around for years mainly used on commercial installations.Personally I only fit it asked for and never offer it,I know I'll get shot down in flames by the pro WC band for that but you are after opinions.Does it heat your house quicker...No Does it help maintain a better temp....It depends on your meaning of better.Does it save on running costs....Jury still out and if it makes 2% difference then you be the judge.Needless to say I'm not a fan.When you feel cold and your house requires heating then stuff the outside temp and turn the system controls to suit your needs. End of sermon.

 

[D_Hailsham]

Be very wary of making too much of small differences is efficiency.

Sedbuk has this warning on their database:

Boiler efficiency tests are subject to measurement uncertainty. Consequently small differences in the efficiency values calculated from them are not significant and should not be relied on when comparing boilers. Statistical analysis suggests that if two boilers have SEDBUK values 3 percentage points apart then there is 95% confidence that the boiler with the higher value is more efficient.

The SAP rating of a house is not the same as the Sedbuk rating of a boiler.

Two identical houses with identical heating systems and boilers. If one house has weather compensation but not the other house, the house with weather compensation will have a SAP rating which is 2 points higher than the other.

 

[ianniann]

I'm surprised the usual suspects haven't already weighed in on this. Perhaps they're all out fixing boilers that people suddenly realised don't work?

Proponents of weather compensation make various claims up to around 20% for the benefits. Much of that potential saving is down to features that don't involve any measurement of the external temperature, primarily automatic flow temperature modulation. They also obviously make their comparisons to a poorly configured and poorly operated standard system. You can achieve much of the benefit by keeping your boiler running at the lowest setting that provides adequate heating, turning it up only in winter if necessary.

Weather compensation, strictly, is a means of fine-tuning the flow temperature modulation function. The intention is to allow lower flow temperatures when the external temperarure is relatively warm (for efficiency) and higher flow temperatures when it is cold (for comfort). The 2% figure you've seen is probably an attempt to quantify purely this fine-tuning improvement on an otherwise properly configured modulating system.

Much of the potential efficiency gains or savings rely on human perception of wamrth and the ability to turn down the thermostat slightly. Modulating systems should overshoot their set temperatures by less, theoretically allowing a more steady internal temperature and potentially a lower thermostat setting, but they may not necessarily be operated that way. Your mileage may vary ...

 

[bengasman]

I'm looking to replace my 20year old heating/water system with a combi and wondered if the external temperature compensation is worth getting in terms of comfort/performance or energy (cash) saving? ....

The simple answer to that is: no, unless you have huge gasbills. It's another thing that needs to be bought, installed, and can break down.
2% is the equivalent of turning the roomstat down 0.5 degrees, which is something you don't notice, costs nothing to install and can not go wrong.
In the domestic market, it's a gimmick that has no real value.

 

[mehran]

don't get confused. 2% sap is an over all saving from all your energy usage. it will equal a greater the 2% saving on your gas bill.

viessmann claim up to 20% saving but if we go for a conservative 5%. then a £1000 gas bill you save £50 a year. over 10 year that is £500.

apply that to your gas bill. if out lay for getting the sensor is not worth the saving then don't get it...simple.

the real problem with installers is they get upset if they think someone is telling them what to think. they think they are getting told off for not doing right.

if you don't fit it, you have done nothing wrong. if you do fit it remember to change labour for fitting it... I change £150 to supply and fit it on top of my boiler install...

 

[mehran]

also this may help:

http://www.viessmann.co.uk/etc/medi...e.File.tmp/6pp Viessmann weather comp web.pdf

 

[bengasman]

don't get confused. 2% sap is an over all saving from all your energy usage.

No, it is not, only on gas, and questionable if it applies to dhw

it will equal a greater the 2% saving on your gas bill.

viessmann claim up to 20% saving

No they don't.
20% additional saving over the 10% saving compared to a late model se boiler which makes 2% of the gasbill.

then a £1000 gas bill you save £50 a year. .

No, it won't

 

[mehran]

SAP rating takes in to a count air-tightness, insulation, heating and hot water cosst. no point have a 100% efficient boiler in a house that leaks 99% of the heat away straight away.

it is a rating 1-100 points not a % scale that equals your gas bill.

if you don't agree about fitting WC then thats is fine but no need to be obtuse about.

also your maths is a bit crap... 20% over 10% does not make 2%

 

[bengasman]

... 20% over 10% does not make 2%

It does where I come from.
20% = 1/5
1/5 of 10% is 2% unless maths have changed since I went to school.
I think you have fallen for the marketing schpiel designed to make it sound better. The wc claim:
additional saving of 20% is based on the 10% gain compared to a se boiler (which is a lot less spectacular than most people think)
And most people overlook the other clever little addition of the marketeers: up to2%

 

[bengasman]

...There is about a 2% improvement on the SAP rating when you add Weather Comp.

Not quite. There is a maximum saving of 2%

You will get an reduction of up to 15% of the space heating bill with weather comp over and above the gain from fitting a condensing boiler without it.

Where do you suggest the savings come from if the average saving of adding wc to a he boiler is about 1%?

If you really want the truth about the actual savings of wc, email a number of manufacturers with the following question.

My gasbill was £765.43 over the past 12 months. My boiler is your model xyz. What is your best estimate of what it would have been if I had wc installed when they fitted the boiler?
You will not get a single answer that quotes an amount under £750.
Most likely you won't get any figure quoted at all, but only excuses like:
"all homes are different"
"can't say with all the changes in gasprice"
"depends on the settings/installation"

 

[GaytonTonner]

I am surprised at the adamant stance by the many here against weather compensation. It is obvious that most of the time the return temperature will be low promoting higher efficiencies over 95% of run time. It puts the heat input near enough to heat output. It gives superior comfort conditions. I fitted a stand alone wc years ago to my place and what I did appreciate was the even temperature in the place. There was no temperature spikes always nice.

Someone wrote it doesn't heat up your house faster. Well it heats up the house to a set rate based on the outsides temperature, as wc matches input to output. Some boilers will override the compensation and ramp up the warm-up temperature, then revert to outside temperature control when the house is warm. The wc is connected to the time clock functions. When switched on it runs up to room temperature setpoint ASAP, then back to wc when near setpoint. This is all invisible top the user, and installers as well it appears.

I advise most to find out more about wc and fit it as a matter of course. Probably they do not want to fit the outside sensor as it entails a wire run and using a ladder in some cases.

 

[bengasman]

...It is obvious that most of the time the return temperature will be low promoting higher efficiencies over 95% of run time. It puts the heat input near enough to heat output. It gives superior comfort conditions.

My installations have oversized rads, which drastically increases the speed of heating up a cold room. It also allows for a permanently low return temperature to the boiler.

Result compared to WC:

1. Higher savings.
2. Greater comfort.
3. What is not there, will not break down, thus higher reliability.

 

[lawrance]

...It is obvious that most of the time the return temperature will be low promoting higher efficiencies over 95% of run time. It puts the heat input near enough to heat output. It gives superior comfort conditions.

My installations have oversized rads, which drastically increases the speed of heating up a cold room. It also allows for a permanently low return temperature to the boiler.

Result compared to WC:

1. Higher savings.
2. Greater comfort.
3. What is not there, will not break down, thus higher reliability.

You really need to understand weather compensation and its benefits. You are trying top justify your lack of knowledge on the topic. Oversized rads is extra cost and more wall space. The extra cost of a an outside senor is negligible to oversized rads - which will rot in 15 to 20 years. So much for breaking down. The comfort is not greater at all. Understand the 95% on part load aspect of heating.

You are implying weather compensators breaks down. They rarely do. Weather compensation keeps the whole system temperature as low as possible which promotes longevity of the system: rad vales, motorised valves, pumps, and all, last far longer at lower temperatures.

It is not worth getting into tit-for-tat with you are you clearly do not understand CH control too well. You are short changing your customers. Get to know wc, it is easy and your customers will thank you for it. What they do like is knowing the outside temperature on the display. In my system I always knew if it was cold outside by touching the rads. Hot? It was cold outside.

I always knew if it was cold outside by touching the rads. Hot? It was cold outside?
and?
A room stat inside does the same as I always know if its cold outside by touching rads, big deal.
I dont care what the temp is outside unless I am going out.
My pegler i-temps and honeywell digi room stat are MUCH more of a money saver than any weather comp!

 

[dumbrill]

Some boilers will override the compensation and ramp up the warm-up temperature, then revert to outside temperature control when the house is warm. The wc is connected to the time clock functions. When switched on it runs up to room temperature setpoint ASAP, then back to wc when near setpoint.

Have you got any examples of controllers that do this? It makes sense in any environment where the temperature is going to be allowed to fall by an appreciable amount, eg. night time