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new boiler: open vent or system boiler
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# 1
tired dad
Old 12-02-2012, 10:12 AM
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Default new boiler: open vent or system boiler

Appreciate some advice here.

Currently have a conventional gravity fed system with floor standing thorn emi conventional boiler (open vented). Looking to upgrade the system to a modern set up.

Its a large house and so a combi is out. Will be using a water cylinder (current one is big enough).

I don't really understand the system boiler vs open vented option.

As far as I can see the only advantage is the loss of an expansion tank in the loft. We have no intention of building in our loft.

Are there any other issues I should understand?

TIA
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# 2
Canucklehead
Old 12-02-2012, 12:54 PM
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Hi.

On the plus side.

Reduces the risk of freezing the f&e tank in the roof (but you still have the main tank).

The system can be pumped harder as there will be no pumping over or air pulled into the system.Improved system circulation with higher pump speed.

Less oxygen in the water so reduce corrosion risk.

In the event of a leak on the system only the contents of the system will leak out, rather than the f&e tank constantly filling.

Downside.

Only one downside really. The system and it's pipework.
The increase in pressure (the pressure relief valve will operate at 3 bar (42PSI ish) will find out any weakness that was quite happy to sit at gravity pressure.

The system will run between 1 and 2 bar.

GSR
Ask to see CIPHE (Chartered Institute of Plumbing & Heating Engineering)
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# 3
ormus
Old 12-02-2012, 12:58 PM
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with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
with the added benefit of one boiler always working in case of breakdown.
Get some gorm.
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# 4
unclebulgaria
Old 12-02-2012, 2:24 PM
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Quote:
Originally Posted by ormus View Post
with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
with the added benefit of one boiler always working in case of breakdown.
Hmm
I personally think that's just a tad overkill, as well as expensive.
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# 5
southcoastrgi
Old 12-02-2012, 2:35 PM
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Quote:
Originally Posted by ormus View Post
with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
with the added benefit of one boiler always working in case of breakdown.
This is the 2nd thread that I've seen where you have recommended someone fit two combi boilers, what is the matter with you, if a house has enough hot water demand to warrant two combis then a combi isn't the right option in the first place, I would never ever fit two boilers in a domestic property, I don't know what you do for a living but if you are in the plumbing & heating industry I bet your customers love you with all your incorrect advice.
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# 6
ormus
Old 12-02-2012, 3:01 PM
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compared to the total cost of a system,
the added expense is fairly small, two small/er combis are not that much more than one large one.
and the benefits are greater than the extra costs.
Get some gorm.
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# 7
tired dad
Old 12-02-2012, 5:05 PM
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The cost of getting 2 mains feeds in the house and siting 2 combi's seems like a lot of hastle to me.

I can see your point of having a system if one fails but I am not at all convinced that combis are the right thing for large houses with multioccupancy.

I will stick to 1 condensing boiler and am just trying to get a feel for the real world differences between a gravity fed open vented boiler or system boiler.

My central heating system is low pressure radiator based and now 25y old. I would be a bit concerned about putting high pressure through that system.
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# 8
southcoastrgi
Old 12-02-2012, 9:06 PM
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Quote:
Originally Posted by ormus View Post
compared to the total cost of a system,
the added expense is fairly small, two small/er combis are not that much more than one large one.
and the benefits are greater than the extra costs.
NO, NO & NO what a b1oody stupid idea
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# 9
southcoastrgi
Old 12-02-2012, 9:13 PM
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tired dad, some good advice & explaination from CH above, i'd just stick with open vented if you are at all worried about the rads or pipework, i've seen rads explode when coverted from open vented to sealed with the increased pressure.
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# 10
garethgas
Old 13-02-2012, 8:22 AM
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Quote:
Originally Posted by ormus View Post
with large houses (two bathrooms) it can make a lot of sense to split the house into two zones and install 2 x combi boilers.
with the added benefit of one boiler always working in case of breakdown.
I don't mean to join in any kind of ganging up, but in 35 yrs, I've only needed to do this twice.
In one case, the meter needed to be replaced with a bigger one to cope with the gas demand.
I think you should reconsider your view on this as its a very rare and unusual situation that would require 2 boilers in tandem.

keithgillyon wrote:
NO, NO & NO what a b1oody stupid idea

Harsh but true I'm afraid.
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# 11
cyclonebri1
Old 13-02-2012, 8:56 AM
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Op, you say the house is too large for a combi boiler??. Just how big is it??

Only last year we fitted a Glow worm combi to my daughters newly extended house. It has been massively extended having 5 double beds 20ft x15ft lounge, large kichen, large dining, 2 bathrooms, 2 kids playrooms, office and open reception.

The combi, excuse the lack of detail as it escapes me at present, copes perfectly well, and would likely be much more efficient now condensing boilers have improved.
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# 12
southcoastrgi
Old 13-02-2012, 2:48 PM
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Quote:
Originally Posted by cyclonebri1 View Post
Op, you say the house is too large for a combi boiler??. Just how big is it??

Only last year we fitted a Glow worm combi to my daughters newly extended house. It has been massively extended having 5 double beds 20ft x15ft lounge, large kichen, large dining, 2 bathrooms, 2 kids playrooms, office and open reception.

The combi, excuse the lack of detail as it escapes me at present, copes perfectly well, and would likely be much more efficient now condensing boilers have improved.
It's not generally to do with the size of the house with regard to the heating circuit, it's all to do with the hot water demand, most domestic combi's only go upto 40kw & this will give approx 16ltrs/min @ 35 degree rise, if you have multiple hot water outlets running at the same time, ie showers, taps, bath etc a combi won't cope as all the outlets will suffer from a red flow & in some cases stop altogether, this is why every house should be surveyed in it's own right, yes combi's are great in the right circumstances but they are not suitable for all applications.
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# 13
cosworth_monkey
Old 13-02-2012, 3:34 PM
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Agreed with what Keith has said, combi boilers are great for the right situation but won't perform under high hot water demand.

Also in regards to fitting two boilers, I've only had to do this once in a domestic property and even then it was only because a consultant had convinced the owner it was the right thing to do...ormus, you weren't the consultant were you?!
Lightbulb Moment 17/09/2006
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# 14
cyclonebri1
Old 13-02-2012, 6:28 PM
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But the size of the house does dictate the hot water requirement, ie, a 1 bed flat will have a shower, a 2bed semi a bathroom, a 3 bed a shower and bath, 4 bed 2 baths etc etc.

The unit we fitted was around 130,000bth, into the heating of course, that is roughly the 40KWs mentioned, and 100,000 into the DHW, it works fine,
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# 15
Mr Ted
Old 13-02-2012, 7:00 PM
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System boiler every time as far as i am concerned, but have the system pressure tested, which should be tested to twice the maximum working pressure!

Boiler operation is little affested other than the odd occasion that a system or pressure vessel top up being needed!

I would also go for a sealed DHW cylinder to give a much better constant water pressure throughout the property and this will also give virtually equal hot and cold water pressures ideal for showers!

There are many high efficiency/recovery DHW storage cylinders/tanks available, such as Megaflow and Gledhill!

As for 2 boiler installations, that is only usually necessary for commercial requirements???
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# 16
southcoastrgi
Old 13-02-2012, 7:59 PM
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Quote:
Originally Posted by cyclonebri1 View Post
But the size of the house does dictate the hot water requirement, ie, a 1 bed flat will have a shower, a 2bed semi a bathroom, a 3 bed a shower and bath, 4 bed 2 baths etc etc.

The unit we fitted was around 130,000bth, into the heating of course, that is roughly the 40KWs mentioned, and 100,000 into the DHW, it works fine,
no it doesn't at all, i've worked in 5 bed houses with only one bathroom & one person living in it, each situation is different, sometimes a combi is the right way to go, sometimes an unvented cylinder is the right way & sometimes a vented cylinder with roof tanks is the best way, that's why it is best to ask someone to do a site survey & see which is the best option.

i'm not saying your situation doesn't work for you & you are happy with it, but just because it does work for you that's not to say it's gonna work for someone else, each house & family are different.
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# 17
cyclonebri1
Old 13-02-2012, 8:41 PM
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Quote:
Originally Posted by keithgillyon View Post
no it doesn't at all, i've worked in 5 bed houses with only one bathroom & one person living in it, each situation is different, sometimes a combi is the right way to go, sometimes an unvented cylinder is the right way & sometimes a vented cylinder with roof tanks is the best way, that's why it is best to ask someone to do a site survey & see which is the best option.

i'm not saying your situation doesn't work for you & you are happy with it, but just because it does work for you that's not to say it's gonna work for someone else, each house & family are different.

Keith, I didn't say it was a one size for all. I simply said it worked for us in reply to the op that said his house was toooo big??, you dig??
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Will the grammar and spelling police respect I do make grammatical errors, and have carp spelling, no need to remind me.

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# 18
southcoastrgi
Old 13-02-2012, 8:56 PM
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Quote:
Originally Posted by cyclonebri1 View Post
Keith, I didn't say it was a one size for all. I simply said it worked for us in reply to the op that said his house was toooo big??, you dig??
i'm not going to get into a confrontation over this, i suggest you read your own posts, then sit down & have a conversation with yourself about what you really meant to say, groovy baby !!
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# 19
Mr Ted
Old 13-02-2012, 9:41 PM
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Hell how am I gonna cope

I got a 1 bedroom house and a lorry load of tennants movin in soon

Better get at least 4 more boiler installed
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# 20
southcoastrgi
Old 13-02-2012, 10:32 PM
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Quote:
Originally Posted by Mr Ted View Post
Hell how am I gonna cope

I got a 1 bedroom house and a lorry load of tennants movin in soon

Better get at least 4 more boiler installed
Mr Ted, that is the quote of the year, i take my hat off to you sir
I'm only here while i wait for corrie to start.

You get no BS from me & if i think you are wrong i WILL tell you.
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