Conflicting Opinions - a Low Loss Header or not?

[Chris43]

I'm in the position of having to replace my 31 year old boiler in my large-ish detached house. The heating system itself is old, with a mixture of old iron pipes and newer copper ones, 20 radiators in all. The old boiler was a 125,00 btu, or 35KW, an Ideal CF120.
I can imagine that its efficiency at the end of its life wasn't great, so I am expecting rather better from a new Condensing boiler.
I have three quotations so far, all varying in term sof what is recommended. I think I can work my way through most of the differences (mostly about use or not of existing pumps, hot water tanks, controls etc.).
But one quotation is different in that it offers, as an option, the installation fo a low loss header and sump pump. The explanation is that because my pipework is old, the engineer cannot guarantee input and output temperatures of the boiler and as a result the boiler may not run at its optimum efficiency. It is implied that the boiler life might be shorter because of this, and may be less reliable. When pushed, a figure of 15% loss of efficiency is being quoted.

I've done a lot of Googling, and some of these claims appear to be valid, although all articles seem to reference commercial multi-boiler installations not a domestic one.

I would appreciate it greatly if someone could shed light on whether these claims are correct for my size of boiler and system?

If they are, the option price of £1500+vat seems to me to be a high charge? I have checked a few websites, and the actual header and pump appear to be around £400, so it seems that another few days worth of work is being suggested. A bit high perhaps?

Thanks in advance.

 

[ironman1]

Simply put , a low loss header is usually installed where multiple zones are being used , one of the reasons for low loss headers is to avoid stratification accross the heat exchanger/s , shunt pump will have to be sized in accordance with system load & can get pretty costly , in you're case it would be beneficial to install two seperate boilers , one for heating & one for hot water............lots more to it but hope you get the idea.

 

[Agile]

In a very simple way the LLH enables the boiler to operate independently of the flow to the heating circuits so it cannot suffer from reduced flow.

The heating circuits then draw heat from the LLH as required.

I have not seen and tested enough LLHs fitted on condensing boilers to be convinced that they enable the boiler to operate at optimum condensing efficiency. Those who fit them seem to me more interested in ensuring the boiler operation is not compromised by varying heat requirements rather than optimum efficiency.

Your system is only a larger domestic and may well not need the same power as the previous boiloer. It needs a calculation to see what the whole house heat loss is.

I would expect a 24 kW or 28 kW may well be adequate.

Tony

 

[Chris43]

I now understand what the LL header does, but would it be needed because of the old pipework and radiators? I'm being told that if they were to replace everything, then they would design it specifically and so they would be able to match the system to the boiler correctly.

Because they are joining into an "unknown" pipework and radiator system, they don't want the boiler to be compromised because of it.

Are they being over-cautious, or trying to sell me somethig I don't need, or what? And, any price comments, bearing in mnd they will be renewing the boiler pipework anyway.

Thnks in advance again.

 

[Agile]

I am sure they are concerned about the boiler being able to ensure the boiler copes with the varying loads.

I dont see that the LLH will be significant in dealing with a dirty system. That would need power flushing and filters.

My view is that a LLH is not required ( although it would adsolve the installer from boiler problems at the expense of efficiency. )

I cannot comment on the costs involved because I dont know whats involved but it does seem a biut expensive to me.

Tony

 

[transam]

If u are worried about old iron pipes & radiators dirt in system ect seperate the boiler from the existing system by useing a plate exchanger & heat it indirectly ? maybe ?

 

[Agile]

You can fit a wall hung condensing boiler with built-in weather compensation, such as a Viessmann Vitodens 200-W 35kW. It can be flued through your existing stack if required. It has its own on-board diverter valve and controls.

Are you saying that it can be used as an open flued boiler?

Is that only when a flue liner is fitted?

If thats the case can you give a link to appropriate details?

Tony

 

[ajrobb]

With W-plan, separate control of flow temperatures for CH and DHW and some form of weather compensation for CH flow temperature, I doubt you'll need to worry about keeping the temperature rise across the boiler close to 20°C. This is typically only for full power. With modulating flow temperature, the boiler efficiency is less sensitive to flow rate than with fixed flow temperature (typical S-plan).

With an old system, I'd be more worried about heat loss from poorly lagged pipes outside the heated envelope (e.g. below suspended ground floor or in the roof space). Perversely, these are more efficient with high fixed flow temperature controlled by a room thermostat. As the new boiler modulates the flow temperature down, the proportion of heat lost outside the heated envelope actually increases as the heating is on continuously rather than intermittently. You can get some idea of the heat your losing by comparing the flow temperature at each radiator with the flow temperature from the boiler and comparing that difference with the difference across the radiator. TRVs also increase the proportion of heat lost outside the heated envelope.

 

[Agile]

I doubt you'll need to worry about keeping the temperature rise across the boiler close to 20°C. This is typically only for full power.

I take the view that the problem is to keep the return temperature down to promote higher efficiency.

The only normal way to do that is to have a high temp differential at the boiler.

I dont see how thats likely much of the time with a LLH.

Tony

 

[holty]

If u are worried about old iron pipes & radiators dirt in system ect seperate the boiler from the existing system by useing a plate exchanger & heat it indirectly ? maybe ?

i would second that. you could aslo have the luxury of having a system boiler combined with open vent heating system. in an ideal world your system should be cleansed for good effeciency. but in reality. really dog systems can dislike flushing and cause more problems. least with transams option it will stop the boiler from getting hit hard with dirt.

 

[Agile]

What type of HE and at what cost for a 30 kW system.

What diff could you expect across the boiler side?

Tony

 

[ajrobb]

Ah, but with modulating flow temperature, the return temperature goes down with flow temperature.

For an 'old-fashioned' S-plan installation with a fixed flow temperature of 70°C and a return temperature of 50°C, only about 25% of the heat exchanger will be below the flue gas dew point of 55°C and thus condensing. If the temperature rise is only 15°C then none of the heat exchanger is below dew point and condensation will not occur in the heat exchanger. It is important to optimise boiler flow rate for these systems just to get ANY condensing savings at the set flow temperature. However, as the output power modulates down, the temperature rise drops so the return temperature rises and condensation stops again.

With a 'modern' W-plan installation with modulating flow temperature, flow temperature drops as outside temperature rises. Once the flow temperature drops below 55°C, the whole heat exchanger will be condensing. As flow temperature drops below 55°C, the condensing efficiency increases still further.

The Viessman Vitodens 200W with Lambda control can be 20% more efficient than some Band-A boilers (108% nett efficiency compared to 90%, 108/90 = 1.2 or 20% more).

 

[Chris43]

Sorry guys, but I'm not a heating engineer, so all the jargon, abbreviations etc I am just finding more confusing.

The proposed boiler is a Broag Avanta 30V. I have no doubt that to replace more of the system might be better, and maybe a Vaillant boiler would be better than a Worcester but perhaps a Veissman would be better still. That isn't a debate I want at the moment, unless the consensus is that I do need a LL Header and a specific boiler works better with such an addition.

Please, simple advice, please. Should I go with the low loss header option? and if so is £1500+Vat a reasonable price. It would be great to get a Yes/No on the first and a No, it should be closer to £x for the second.

 

[heatingman]

LLH won't help protect new boiler from old system, have a plate heat exchanger, decent quality from SWEP. Get it encased in Cellotex and jobs a goodun. It will not cost £1500 extra.

 

[holty]

have a look at heatweb.com and go to the plate heat exchanger section. click at the bottom of the page on plate heat ex editorial link. this will give a good description of the use of a plate heat ex.