From Gravity System to Unvented Indirect Hot Water Cylinder

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Hi
I am planning to install unvented indirect cylinder. ATM I have gravity system, cold water tank feeding HWC and F&E tank for central heating in the loft. The mains water coming into the house is with 15mm copper pipe, pressure 4 bar
I understand I need expansion vessel for the unvented cylinder to get main pressure hot water of max 3 bar. I want to know whether I can keep the F&E in the loft meaning keeping the central heating on gravity as it is at present?
TIA
 
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1. You don't necessarily need an expansion tank for an unvented cylinder. Some (e.g. Heatrae Sadia Megaflow) have a built in expansion space.
2. As Cross Thread says, you can keep the F&E. Personally I wouldn't as sealed systems tend to stay cleaner than open vented ones.
3. The incoming cold mains pressure should be a minimum of 2 bar DYNAMIC. This is with another mains fed outlet running while the pressure is measured. You should also be looking for a flow rate of around 20 litres per minute.
4. When you say you are ".. planning to install....." I presume you mean you are getting it installed by a G3 qualified engineer who can also handle the notification to your local building control department. Installing these cylinders is not a DIY job and is notifiable.
 
That's good I can have open vent central heating because my worry was leaks in a pressurised CH system as old plumbing in the house probably over 30-40 years.

I didn't say in my first post, I had 2 quotes, one saying it needs 2 expansion vessels, one for each HW and CH, they were 2 partners came together both gas registered showed me one of their cards so don't know why they said that.
The second guy said I can keep open vent CH no need for a second vessel. He also measured water pressure from garden tap, he had a hose with pressure gauge showed 4 bar, he said that's very good he doesn't see in many places in London.
 
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Second chap seems to be on the ball

An ideal UV cylinder would result in cold water off the mains at the kitchen sink, rest of the taps in the house would have cold feed at the same pressure as the hot water taps. Do get the chap to connect the immersion heater as often this is left disconnected. When boiler fails no immersion heater either.

Expansion vessel or expansion gap is there to take up the expansion of water in the cylinder when it is being heated.
Prudent to leave boiler as open vented. Your cold water storage cistern will be redundant.

You planned cylinder will NOT work if the cylinder is heated by gravity circulation
 
Not to be a wet blanket but did the chap do the pressure test with other outlets running? If not then that's a standing pressure reading, which doesn't tell us much when it comes to how an unvented may perform, you need to know the dynamic pressure, how the mains sustains the pressure when more than one outlet is open at a time. Also did anyone do a flow test - again with more than one outlet open to test the dynamic flow, especially if the mains is 15mm.

BTW I would highly doubt the actual mains to the property is 15mm, though your pipework from the internal stop tap to the rest of the house may be 15mm. Ideally the supply into and out of the unvented would be 22mm, to maximise flow.

Also just to qualify the other chaps - running a fully pumped open vent (OV) CH system has nothing to do with whether you can have an unvented HW system. The HW cylinder can be run on either sealed or OV.
 
The actual mains to the property is 15mm, see the 2 pics.

I have a PRV pressure reduce valve on a cold pipe in airing cupboard , reads 2 bar dynamic pressure.

IMG_5106.jpg

IMG_5107.jpg
 
That's 15m copper - very unlikely that is the actual mains pipe size - you may find that underneath that floor/property that the mains (MDPE/Alkathene/Lead) is larger and it transitions to 15mm before coming up through the floor. That tap is also not one of the standard mains stop taps.

15mm would not normally be a standard water main transporters chosen pipe size @ or from the outside toby.
 
I don't know what's underneath, all I can see 15mm pipe coming into my house as in pics what I said in my first post, which matters. I am not going to dig and find out as not relevant.
 
I don't know what's underneath, all I can see 15mm pipe coming into my house as in pics what I said in my first post, which matters. I am not going to dig and find out as not relevant.
It will be very relevant if pressure is lacking.
 
He also measured water pressure from garden tap, he had a hose with pressure gauge showed 4 bar, he said that's very good he doesn't see in many places in London.
If this gauge was just connected to a tap and that tap opened without any other taps flowing and there were also no flow readings taken, with at least one other tap open, then that information on it's own is completely useless and shouldn't be relied on to decide whether the mains could support an unvented cylinder or not.
It ain't relevant and it won't be relevant in may case. Pressure is as stated above.
Wrong ... It's one of the most relevant thing to understand before considering an unvented install. Of course though , that's why you're are posting on a DIY site asking us pro's questions about an unvented install because you obviously know better. If you are saying that your proposed installer say's that's not relevant then he doesn't have a clue what he's talking about and honestly shouldn't be working with them.

An unvented cylinder requires a min of 15>20L/Min @ a min of 2 bar dynamic. If the mains cannot deliver that to where the cylinder is being located, it is a waste of money installing one as it will never perform as it should.
 
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If this gauge was just connected to a tap and that tap opened without any other taps flowing and there were also no flow readings taken, with at least one other tap open, then that information on it's own is completely useless and shouldn't be relied on to decide whether the mains could support an unvented cylinder or not.

Wrong ... It's one of the most relevant thing to understand before considering an unvented install. Of course though , that's why you're are posting on a DIY site asking us pro's questions about an unvented install because you obviously know better. If you are saying that your proposed installer say's that's not relevant then he doesn't have a clue what he's talking about and honestly shouldn't be working with them.

An unvented cylinder requires a min of 15>20L/Min @ a min of 2 bar dynamic. If the mains cannot deliver that to where the cylinder is being located, it is a waste of money installing one as it will never perform as it should.
Not relevant, read my first post to what was my question.
 
Not relevant, read my first post to what was my question.
and you had the answer in post #2

Others have been trying to guide you in making an informed decision on the unvented (so as to avoid problems / disappointment down the line) and arm you with info to ask your potential installers.

But you don't seem want to take that on board and in the spirit it was intended...
 
and you had the answer in post #2

Others have been trying to guide you in making an informed decision on the unvented (so as to avoid problems / disappointment down the line) and arm you with info to ask your potential installers.

But you don't seem want to take that on board and in the spirit it was intended...
I know the rest, done my homework on these elsewhere inc manufacturer

Are you a pro? If so, it's 11am go back to your work leave the forum alone :LOL:
 

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