Installing Combi Boiler on Rads only

Wavey

Evening all.

I need to replace my external oil fired boiler and was looking at buying a combi boiler.

I'm not in a position to tie into the hot water taps in the house yet so is it possible to only tie in to the rads circuit for now and cap off the other flow and return on the boiler?

I can then tie in to the hot water tap circuit in the future?

Can anyone recommend a good supplier?

I was looking at THIS.

Or would it be cheaper to buy from an Irish supplier like Grants in Birr? they have no prices on the site. But will give them a ring tomorrow.

Thanks,

Wavey.

Kevin007

Hi Wavey
There are some excellent combi boilers on the market but they are all Cast Iron and this is what you should buy if efficiency and running are your criteria
There are a lot of junk steel boilers out there, some of them made in Ireland and none of them any good and to really confuse the public they quote boiler efficiency figures which are totally misleading. I have never seen a steel boiler which has a working efficiency in excess of 60% and most of them are around 50% whilst a good cast iron at nearly the same money and set up by a commissioning service engineer who knows his stuff can achieve a working effic. figure up to 80%. This is the maximum Effic. that any boiler can achieve Do not go for Condensing Oil as condensation in all appliances only works up to 57deg.C Above this Temperature no condensation occurs and you cannot run an oil boiler below 60degC otherwise sulphur and carbonic acids condensing in the chamber will eat the bottom of your boiler in no time. Good Hunting

JamesM

Kevin007 wrote: »

Hi Wavey
There are some excellent combi boilers on the market but they are all Cast Iron and this is what you should buy if efficiency and running are your criteria
There are a lot of junk steel boilers out there, some of them made in Ireland and none of them any good and to really confuse the public they quote boiler efficiency figures which are totally misleading. I have never seen a steel boiler which has a working efficiency in excess of 60% and most of them are around 50% whilst a good cast iron at nearly the same money and set up by a commissioning service engineer who knows his stuff can achieve a working effic. figure up to 80%. This is the maximum Effic. that any boiler can achieve Do not go for Condensing Oil as condensation in all appliances only works up to 57deg.C Above this Temperature no condensation occurs and you cannot run an oil boiler below 60degC otherwise sulphur and carbonic acids condensing in the chamber will eat the bottom of your boiler in no time. Good Hunting

Can you explain yourself a bit better please.
Are you talking about 60degC water temp ? The gasses that run through the baffles of a boiler are a lot hotter than that. What happens to the boiler in the half hour while the water is coming up to 60degC. I have seen a steady flow of water from condensing boilers set at 70degC. What about the difference between the temp of the gasses in the chamber and the flue of a condensing boiler - there is a huge difference. The gasses condense as they exit a condensing boiler because so much heat is extracted from them as they travel through the baffles and tubes. The second chamber of a condensing boiler is made from stainless steel, so that it won't corrode.

I am not sure that a condensing boiler is worth the extra cost and complication, but I have seen many steel boilers that are nearly 40 years old.
Most of the cast iron boilers from the late 60s and early 70s burst within 20 years.
Jim.

Wavey

Thanks for the advice guys.

With regards to sizing the boiler what is the best way to do it?

I have 9 rads in the house but would only run 5 of them at a time.

Would this requires a 20, 25 or 30kW Boiler?

Thanks,

Wavey.

JamesM

I'm more a BTU (old) person. You can do the full measuring radiator area thing, but I think that a 50/70, or at the most a 70/90 would be suitable.
Jim.

copper12

A lot of people don’t realize’ that replacing an old boiler’ with a condensing boiler’ would, in order to get the maximum return on there investment; mean that either' the radiators’ should be replaced for lager radiators; or the boiler undersized
The efficiency of these boilers; either natural gas, petroleum gas, or oil, are different;
Natural gas’ being the most efficient , followed by petroleum, then oil
If the installer; cannot’ maintain a differential of 20 degrees’ between the flow and return; then the boiler is not running at it’s most efficient.
Combi boilers, running in hot water mode; irrespective of make, do not operate in condensing mode

JamesM

Maybe this whole condensing thing has gone completely over my head.
I am not a plumber, a fitter, or a heating engineer, so I am not speaking with authority.
BUT, I cannot understand the mystery about condensing boilers.
An oil boiler is a water tank with a burner firing a flame into the lower end of it. There is water circulating in the walls. This water is heated and then circulated around the radiators.
The hot gasses from the flame go up through the boiler and out the flue (up the chimney).
In a 30 year old boiler the gasses go straight up and out the flue without much resistance.
In a modern standard boiler, the gasses weave their way up through a series of baffles, transferring more heat out to the water, and then out the flue.
In a condensing boiler, the gasses go up through the baffles and then into a separate chamber (made of stainless steel, so that there will be no corrosion), extracting even more heat from the gasses, and then out the flue.
In this last chamber, so much heat has been taken out of the gasses that they condense, and water drips down the sides of the chamber and is drained out of the boiler.
As I understand it, this boiler can be used for under-floor heating because the boiler can be run at a low temperature, without causing corrosion. It can also be used for a normal heating system, because it will extract more heat from the gasses (than a standard boiler) before they exit through the flue. And therefore will be more efficient.

Now, I am quite prepared to listen to someone who can tell me I am wrong.
Jim.

copper12

James m your 90% right
It’s the dew point of these gasses that heat it taken from; that’s why the return temperature is so critical
Manfacttures make there clams’ of over 90% by capturing this heat;
A condensing boiler; that is not condensing; is no more efficient’ than an ordinary high efficiency, non condensing boiler; but the price now that’s a different story

311

JamesM wrote: »

Maybe this whole condensing thing has gone completely over my head.
I am not a plumber, a fitter, or a heating engineer, so I am not speaking with authority.
BUT, I cannot understand the mystery about condensing boilers.
An oil boiler is a water tank with a burner firing a flame into the lower end of it. There is water circulating in the walls. This water is heated and then circulated around the radiators.
The hot gasses from the flame go up through the boiler and out the flue (up the chimney).
In a 30 year old boiler the gasses go straight up and out the flue without much resistance.
In a modern standard boiler, the gasses weave their way up through a series of baffles, transferring more heat out to the water, and then out the flue.
In a condensing boiler, the gasses go up through the baffles and then into a separate chamber (made of stainless steel, so that there will be no corrosion), extracting even more heat from the gasses, and then out the flue.
In this last chamber, so much heat has been taken out of the gasses that they condense, and water drips down the sides of the chamber and is drained out of the boiler.
As I understand it, this boiler can be used for under-floor heating because the boiler can be run at a low temperature, without causing corrosion. It can also be used for a normal heating system, because it will extract more heat from the gasses (than a standard boiler) before they exit through the flue. And therefore will be more efficient.
Now, I am quite prepared to listen to someone who can tell me I am wrong.
Jim.

Your spot on jim.

At the moment I'm really pushing the worcester greenstar on people ,it's a natural gas condensing boiler.
Basically when the greenstar reaches temperature ,the whole boiler reduces in combustion. This includes the fan aswell. The boiler is not audible at all when running at temperature ,it never powers down so it doesn't have the high costs of raising the temperature again.

It's definetly got to do with the fuel more than the process. I couldn't ever see a boiler work as effeciently with oil as the greenstar boiler.

http://www.worcester-bosch.co.uk/homeowner/products/gas-fired-boilers-and-systems/greenstar-15ri

Micky Dolenz

copper12 wrote: »

A lot of people don’t realize’ that replacing an old boiler’ with a condensing boiler’ would, in order to get the maximum return on there investment; mean that either' the radiators’ should be replaced for lager radiators; or the boiler undersized

I don't agree. As long as you have 20 degrees differance between flow and return, it will be efficient. see here: http://www.abacusgas.com/condensingmyths.pdf

copper12

I couldn't ever see a boiler work as effeciently with oil
you wont it's to do with the dew point of the flu gases
oil has a mush lower dew point natural gas the highest
New builds replacement of very old boilers especially gas boilers I would agree with
However I have seen to many boilers under five years old replaced because f the myth that the condensing will save money the new boiler would be twenty years ld or older before the cost cold be recouped .
Potterton baxi vokara and many mre say there non condensing boilers between 78% and 85% depending on boiler type
abacusgas are only interested in selling and installing boilers
of coerce they would want you to replace you existing boiler.
Myth: they are harder to maintain
ask any tec and they will charge extra to service a condensing boiler
If it needs to be repaired then think in hundreds of Euro for the repair
Myth: they are only efficient when fully condensing
This is typical of sales talk you buy a condensing boiler it doesn’t condense and they have the check to tell you it’s still more efficient that a boiler with an efficiency of 80% or more how much will this save you 10 cents a day most likely less
Myth: they are to expensive
This is a fact not a myth
There may be a grant good luck in trying to obtain it
The pay back period will then be minimal 4 years
If you don’t get the grant would this extend to 14 or 24 years
Myth: they nee lager radiators
In most systems radiators are all ready over sized
This is blatantly misleading
A marginal benefit of only 3% may be obtain from over sizing radiators for a new system as this will allow slightly cooler return water to the boiler and maximise time spent in condensing mode but this is usually uneconomic and impractical
I have never heard so much rubbish
They are contradicting themselves

The whole point of installing a condensing boiler is to maximize it’s efficiency designing the system is both practical and necessary
The whole point in this is to have the return to the boiler as cool as possible
Just having a differential of 20 degrees doesn’t work either
For a gas boiler the return should be between 50 and 60 degrees

Micky Dolenz

I wasn't disagreeing on your oil point.

20 degrees is what is recommended to give a better pick up of latent heat allowing condensing to take place. This will be acheived regardless of the water temperture as long as the differance is constant, hence the need to balance systems.

copper12

20 degrees is what is recommended to give a better pick up of latent heat allowing condensing to take place. This will be achieved regardless of the water temperature as long as the differance is constant, hence the need to balance systems.
Your right 20 degrees is what’s recommended
For a gas condensing boiler to to operate efficiently this differential needs to be maintained .
The dew point of the flu gases in a natural gas boiler is around 50 degrees this is the magic figure
In order to achieve this it’s recommended that the return should be kept below 60 degrees
When installed in real houses, the performance of condensing boilers is typically 4-5% lower than in laboratory tests by groups such as SEDBUK.[3] This gives typical seasonal efficiencies of 82-89% in the UK (HHV). Part of the efficiency drop is because boilers are often oversized for the thermal demand of the property, giving return temperatures over 50°C from the heating system, which prevents significant condensation in the heat exchangers

Micky Dolenz

Very well put.

I belive most systems, new or old, can quite easily meet the conditions to promote condensing. Return wouldn't be higher than 60d normally. Condensing boilers can be fitted to most systems with little or no adjustment to the system.

311

copper12 wrote: »

[/SIZE]When installed in real houses, the performance of condensing boilers is typically 4-5% lower than in laboratory tests by groups such as SEDBUK.[3] This gives typical seasonal efficiencies of 82-89% in the UK (HHV). Part of the efficiency drop is because boilers are often oversized for the thermal demand of the property, giving return temperatures over 50°C from the heating system, which prevents significant condensation in the heat exchangers

Most decent boilers have modulating valves ,so the boiler will only ever give the heat required.
What boilers do you commission by the way?

copper12

At the moment I'm really pushing the worcester greenstar on people ,it's a natural gas condensing boiler.

Good boiler I have there CD
http://www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_hxzyglrac_1169847541
It’s links like the one above its here you will get the real information

311

copper12 wrote: »

At the moment I'm really pushing the worcester greenstar on people ,it's a natural gas condensing boiler.

Good boiler I have there CD
http://www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_hxzyglrac_1169847541
It’s links like the one above its here you will get the real information

Real imformation for what exactly ? ,I've installed about 8 of them in the last fortnight.
They are the best boiler on the market at the moment ,I don't need the internet to tell me that.

Edit : Flow rates on combi boilers differ from one another ,a passage from a website doesn't tell the whole story I'm afraid.

copper12

Quote Real information for what exactly ?
On weather people’ who buy these boilers’ are satisfied with there performance . Do they perform to there expectations .
If not; were they misled’ by the sales literature’ or the installer .

They are the best boiler on the market at the moment ,
That’s your opinion and your intituled to it others may think differently
I don't need the internet to tell me that.
Where else’ can you get unbiased information; from installers?


Edit : Flow rates on combi boilers differ from one another, ?
a passage from a website doesn't tell the whole story I'm afraid.
I would agree with you totally

manonditch

Hi all you knowledgable guys.
On of the (painted) side panels of my oldish oil boiler is corroded away i.e there is a big hole in it. But the boiler works fine. What should I do?