Is a 25KW Condenser Gas Boiler Sufficient?

thebigbiffo

Hey All,


I'm currently getting a few quotes for a new gas boiler and I’ve had a fairly large gap in prices and want to make sure the cheaper quote suffices. My house is about 1800 sq foot with 14 rads and obviously the water tank. It runs off a Calor tank that services the entire estate which is metered on our house.

The cheapest quote is for a 25 kw Ferroli boiler, no electrician needed, no cleaning/system flushing needed. Guy is an agent for this boiler company and I think it’s a nixer.

The other quote is for a 30 kw (Not 100% on the make, but will revert) and has an allowance for an electrician and for flushing the system.

The difference in quotes is the not insignificant sum of €800.

My questions are: would 25kw definitely be enough for this house size and that many rads (this is the most important point!)? The house is only about 5 years old, is the flushing necessary (the first, cheaper quote says it’s not)? Also, the first quote guarantees parts and labour year one, parts only years 2 whereas the second quote is parts and labour for 5 years.

I’m very tempted to go with the cheaper option obviously, but would love to see what the opinion on here is on whether it’s worth paying more for the extra guarantee, flushing the system etc. Like why does one guy need an electrician and the other doesn’t?

Thanks in advance for any help, advice or general thoughts on this!

knighted_1

ferolli are a brand I wouldn't put in a house , cheap and prone to problems

without seeing your house can't comment on 24kw but with 14 rads I would opt for the 30 kw , should be modulating .

think you know yourself the system has to be flushed to comply with most warrentys nowadays and you know the first guy sounds like a chancer ( nixcer)

if you want to pm me both amounts I will give you an opinion on weather it's value or not

thebigbiffo

thebigbiffo wrote: »

My questions are: would 25kw definitely be enough for this house size and that many rads (this is the most important point!)?

You need to trust your installer:), if you can't then find one you can.

thebigbiffo wrote: »

is the flushing necessary

yes, decent installers will always power flush a system as in the past inhibitor was not normally used, leaving a heating system dirty

thebigbiffo wrote: »

Like why does one guy need an electrician and the other doesn’t?

a lot of installers don't wire heating systems.



The things I would be looking at would be weather compensation, gas supply pipework big enough for boiler,heating controls that allow running the heating at a lower temperature that doesn't impact on the hot water temperature, good service back up and long warranty.

thebigbiffo

Thanks for the responses folks.

knighted_1 wrote: »

ferolli are a brand I wouldn't put in a house , cheap and prone to problems

without seeing your house can't comment on 24kw but with 14 rads I would opt for the 30 kw , should be modulating .

think you know yourself the system has to be flushed to comply with most warrentys nowadays and you know the first guy sounds like a chancer ( nixcer)

if you want to pm me both amounts I will give you an opinion on weather it's value or not

Wow I’d no idea Ferolli were a cheap brand – do you know of anywhere where there’s a ratings site or anything for gas boilers so I can see what kind of problems arise? The chap doing the job is the official Irish agent for Ferolli – surely if he says the warranty stands without flushing he’s be correct?

I’ll bang the PM over in a minute.

gary71 wrote: »

You need to trust your installer , if you can't then find one you can.

yes, decent installers will always power flush a system as in the past inhibitor was not normally used, leaving a heating system dirty

a lot of installers don't wire heating systems.

The things I would be looking at would be weather compensation, gas supply pipework big enough for boiler,heating controls that allow running the heating at a lower temperature that doesn't impact on the hot water temperature, good service back up and long warranty.

The cheaper guy came recommended – his credentials seem good (at least being the agent and service person for a popular boiler system would make me think so) and he just seems like a nice fella so I sort of do trust him. He reckoned that because the system is only 5 years old flushing is probably unnecessary and he did mention the inhibitor would be added…I think. I know the other guy because he’s been to my house a few times and do trust him as well.

The long warranty – of full parts and labour - is very attractive, but I’m wondering if it’s worth the difference! Do you have an opinion on Ferolli? Whats ‘water compensation’? Gas supply should be fine (again, new house), heating controls are currently run by a computer board which separates out upstairs, downstairs and water, warranty’s as above…

I’ll PM both you guys the quotes.

heinbloed

The output of the new boiler should not exceed the actual demand.
To find out out what the demand is a heating engineer would be the right person to ask. The number of radiators is irrelevant.

What went wrong with the 'old' boiler? 5 years is no age for a boiler.

What was the output of the old boiler, was this sufficient? Was the old boiler 'cycling' ? What type of boiler was the old one (model, brand) ? Are there other boilers or thermal sources connected to the central heating system, like back boilers, ST systems?

Has domestic hot water to be supplied by the central heating system via a heat exchanger in a buffer tank ('cylinder')? Or would a combi-boiler be the right equipment?

heinbloed

For a 5 year old house with a heated surface of 180m2 a 25 kW boiler is propably far oversized. Very far.
You'll heat a tent of the same size with this output.

thebigbiffo

heinbloed wrote: »

The output of the new boiler should not exceed the actual demand.
To find out out what the demand is a heating engineer would be the right person to ask. The number of radiators is irrelevant.

What went wrong with the 'old' boiler? 5 years is no age for a boiler.

What was the output of the old boiler, was this sufficient? Was the old boiler 'cycling' ? What type of boiler was the old one (model, brand) ? Are there other boilers or thermal sources connected to the central heating system, like back boilers, ST systems?

Has domestic hot water to be supplied by the central heating system via a heat exchanger in a buffer tank ('cylinder')? Or would a combi-boiler be the right equipment?

The old boiler was a piece of s'hit right from the get go - never worked properly, we were given the run around by the installer and the developer for a few years until the installer eventually owed up and said the boilers should never have been bought - he passed the blame to the developer who will do nothing about it. It was a 'Gercos' boiler (ever heard of them?), header tank leaking, pressure switch gone, constant error messages and shut downs. Company gone wallop, parts impossible to get from Eastern Europe...chaging it the only option I have...the boom years meant regulation/scruples went out the window, but lets not get into that!

The output seemed to be fine, was/is 30kw i think. No back boilers and no other connections afaik except the water and heating. We have a cylinder in the hotpress which heats the water yes, is this correct as per your question? What is 'cycling'?

Thanks for the response,

thebigbiffo

heinbloed wrote: »

For a 5 year old house with a heated surface of 180m2 a 25 kW boiler is propably far oversized. Very far.
You'll heat a tent of the same size with this output.

far oversized? that's a surprise!

thebigbiffo

thebigbiffo wrote: »

Wow I’d no idea Ferolli were a cheap brand – do you know of anywhere where there’s a ratings site or anything for gas boilers so I can see what kind of problems arise?

Look at the which web site or ask on this site what boilers installers find most reliable.

thebigbiffo wrote: »

The chap doing the job is the official Irish agent for Ferolli – surely if he says the warranty stands without flushing he’s be correct?

No, the requirement for a flush is dependent on the quality of the heating system water, if your original heating system was not flushed properly and no inhibitor was added you could devolpe sludge in only a few months depending on the quality of the water, if the original system was not flushed properly and inhibitor is added or your new installation is not flushed properly and inhibitor is added you can end up with system water that is corrosive to plastic, contamination your new boiler which any damage caused is not covered by a warranty, long story stort he has to flush in some manor.

thebigbiffo wrote: »

I’ll bang the PM over in a minute.

I think you should first decide what type of system you want and then get quotes based on that so it's like for like.

thebigbiffo wrote: »

The long warranty – of full parts and labour - is very attractive, but I’m wondering if it’s worth the difference!

A manufacturer that offers a long warranty is pretty sure it's not going to cause many problems.

thebigbiffo wrote: »

Do you have an opinion on Ferolli?

I don't like Ferrolli, that may be based on my ignorance of the product but also in the Uk they have run out of money and they charge £180 for a service call upfront and if it's a warranty issue they give the money back.

thebigbiffo wrote: »

Whats ‘water compensation’?

Weather compensation allows for the impact of heat from the sun on the temperature of the property, which saves on gas:D.

There are boilers out there that can run at low temperatures for heating allowing the boiler to stay in condensing mode for longer and then fire at a higher temperature for your hot water, this will save you money, a weather compensator will save you money, the more control you have on your heating and hot water the more money you will save, so it's worth while doing your homework now:)

heinbloed

@ thebigbiffo:

"Gerkros" boilers like these:

http://www.orangecrow.com/proj/gerkros/gas_boilers.htm

are designed to run on a pressure of up to 3 bar. In a pressurized system. The existence of a pressure switch-as you have posted- could mean that this type of boiler is NOT suitable to be integrated in a non-pressurized system.

Get the manual to find out, read the label on the boiler.

If so the boiler was never suitable for your open, vented central heating system. An incompetent person (illiterate) had installed the boiler.
So you have a right to be compensated, for ALL costs associated with this faulty installation.
Contact the consumer agency or a solicitor. The case is plain and simple it seems.

Get the data from the boiler and post it here, you might have to open the cover to read the label. Exact model, exact output, exact pressure data etc..

This type of boiler operates as a modulating boiler,according to the data shown in the link above it is modulating between 8 - 25 kW.
With 'cycling' the oparating modus is meant. If a boiler 'cycles' it is overdimensioned, creating more heat than the system can actually get rid off.
A 'cycling' boiler would run for a while, switches off, starts again, switches off, starts again and so on. A bad, inefficient and costly design. Caused by an incompetent specifier.
The thermal and pressure stress caused by such an installation will have it's toll on the boiler's life time.

This 'cycling' must be avoided.

Therefore we use 'modulating' boilers.
Their output starts with the minimum demand (for example 2 kW) and ends with the maximum demand (for example 10 kW).So these correctly sized modulating boilers run as long as the valves at the radiators are open. Only when all valves are closed or the timer kicks in the boiler stops boiling.

A 25 kW boiler for a modern house is - by guesstimation - twice oversized. You could heat 3 or more similar houses with it.
If so it should not have been installed in the first place.

So to get back: Was the old Gerkros boiler cycling, if so under what conditions (all radiators open, demanding)?

Next question:

What was the actual flow temperature ( the temperature in degrees Celsius at the central heating outlet at the boiler) and what was the return temperature ( the temperature in degrees Celsius at the inlet of the boiler) in winter time ?

This is important to know since it makes no sense and is actually dangerous/illegal to install a condensing boiler if it can't be run in the condensing modus.

Third question:

Would it be possible to install a pressurized central heating system in your house supplied by a combi-boiler? Is the distribution system (plumbing and radiators) checked for pressure resistance?

heinbloed

We have a cylinder in the hotpress which heats the water...

Is this cylinder connected to the central heating system?

thebigbiffo

heinbloed wrote: »

@ thebigbiffo:

"Gerkros" boilers like these:

http://www.orangecrow.com/proj/gerkros/gas_boilers.htm

are designed to run on a pressure of up to 3 bar. In a pressurized system. The existence of a pressure switch-as you have posted- could mean that this type of boiler is NOT suitable to be integrated in a non-pressurized system.

Get the manual to find out, read the label on the boiler.

If so the boiler was never suitable for your open, vented central heating system. An incompetent person (illiterate) had installed the boiler.
So you have a right to be compensated, for ALL costs associated with this faulty installation.
Contact the consumer agency or a solicitor. The case is plain and simple it seems.

Get the data from the boiler and post it here, you might have to open the cover to read the label. Exact model, exact output, exact pressure data etc..

This type of boiler operates as a modulating boiler,according to the data shown in the link above it is modulating between 8 - 25 kW.
With 'cycling' the oparating modus is meant. If a boiler 'cycles' it is overdimensioned, creating more heat than the system can actually get rid off.
A 'cycling' boiler would run for a while, switches off, starts again, switches off, starts again and so on. A bad, inefficient and costly design. Caused by an incompetent specifier.
The thermal and pressure stress caused by such an installation will have it's toll on the boiler's life time.

This 'cycling' must be avoided.

Therefore we use 'modulating' boilers.
Their output starts with the minimum demand (for example 2 kW) and ends with the maximum demand (for example 10 kW).So these correctly sized modulating boilers run as long as the valves at the radiators are open. Only when all valves are closed or the timer kicks in the boiler stops boiling.

A 25 kW boiler for a modern house is - by guesstimation - twice oversized. You could heat 3 or more similar houses with it.
If so it should not have been installed in the first place.

So to get back: Was the old Gerkros boiler cycling, if so under what conditions (all radiators open, demanding)?

Next question:

What was the actual flow temperature ( the temperature in degrees Celsius at the central heating outlet at the boiler) and what was the return temperature ( the temperature in degrees Celsius at the inlet of the boiler) in winter time ?

This is important to know since it makes no sense and is actually dangerous/illegal to install a condensing boiler if it can't be run in the condensing modus.

Third question:

Would it be possible to install a pressurized central heating system in your house supplied by a combi-boiler? Is the distribution system (plumbing and radiators) checked for pressure resistance?

heinbloed wrote: »

Is this cylinder connected to the central heating system?

Thanks for the detailed response – I’ll try answer everything I can, but bear in mind it’s coming from a layman, and anything I don’t know I’ll try reply with when I get home like the make/model etc.

Firstly, I’m not sure if it is a pressurized/unpressurized system…this is something to note but is it not something either of these plumbers – especially the chap who’s been to our a house a few time and has no connection with the original installer – would have pointed out to me before? Any chance I have of being compensated will be looked at.

I’m sorry but I’m still not 100% sure about the ‘cycling’ – are you saying that ‘cycling’ by definition is a fault or some boilers are meant to operate like this? How would I know if the boiler was ‘cycling’ or ‘modulating’? If a boiler is meant to ‘cycle’ by design then I don’t think our current/old one was cycling, it would just hum away all the time and I did not notice it stopping and starting (well, not while it was operating anyway – obviously as it kept breaking down it was). It may be worth noting here that there was an automatic valve in our hotpress that a plumber told us was faulty and effecting the boiler working – he replaced it with a manual valve which we would open every time pressure dropped so as the boiler would not shut off due to lack of pressure, which seems to have been the error message we were getting from day one. However, this only worked for a time, then we were told the pressure switch was broken, we could not get that replaced and here we are…

I do not know how I would get a reading for inlet and outlet temps – obviously the display panel would have a temp reading which I assume is simply the water temp the boiler is at (low when switched on increasing to max temp).

On the third question – simply put I would not know. The plumbers talk about condenser boilers only so I’m only assuming this is the type I need. I don’t believe I have ever been advised to check for pressure resistance – it makes senses that this should be done considering the issues always seemed to stem from a lack of pressure – whether this was a faulty pressure switch in the boiler or a pressure problem with the system I don’t know.

Lastly – I do not think the cylinder is connected to the heating system but I could be wrong. How would I know and what would the significance be?

Sorry for my non definite answers – I’m not too well up on these matters as you may have guessed!

thebigbiffo

Come to think of it - we have a have a large pump on the system so this would mean it's a pressurized system yes?

heinbloed

Hm.

I suggest to get a real heating engineer in to check the system.
Various points you have made point towards that the 'usual guy' is incompetent to an extreme.
There should be no pressure loss in a pressurised system. So a filling valve to top up the pressure is used only very rarely, not as a permanent top-up.
The flow and return temperature can be meassured with a thermometer.
The cycling is caused by a thermal underdemand at the room heating side, at the radiators. It is not a fault of the boiler (or caused by it) but caused by a non-correct lay-out of the central heating system. Non-suitable components had been assembled to one system.

Every work done on a (gas)boiler should be protocolled.This protocoll has to be handed out to the operator, the householder.

...– I do not think the cylinder is connected to the heating system but I could be wrong. How would I know and what would the significance be?

The question is very significant. Turn off all electricity supply to the cylinder and see if it still gets warm.

Find the manual for the boiler.

That Gerkros went bankrupt doesn't mean that there are no spare parts available, Gerkros never manufactured boilers. They were branders, not manufacturers.
Similar boilers are still manufactured, your 'plumber' might not be up to date with the real plumbing world. So you still can get most parts. All technically essential parts that is.





Check the golden pages for a heating engineer.
The heating engineer will write for you -on demand- a manual for your personal heating system. A booklet where every single item is explained, every valve, every thermometer, all technical parameters.

heinbloed

Come to think of it - we have a have a large pump on the system so this would mean it's a pressurized system yes?

Then you have a pumped system. A pumping pump causes naturally a pressure.
The term "pressurised system" is not restricted to the presence of a circulation pump. It means that in the CH system is a permanent pressure, higher than naturally occuring.
There should be a manometer somewhere showing the actual pressure, for example at the boiler.