Unvented or vented ?

[ToughButterCup]

I'm currently researching instantaneous water heaters, and in that context I  discovered that there are both unvented water heaters and vented ones.  A bit more research shows that whole plumbing systems can be either vented or not.

 

Whassa difference?  Why would anyone choose one system type over the other? 

[PeterW]

Vented water heaters are normally fitted above the counter as they fill using a valve system. Unvented can be fitted anywhere above or below and tend to have smaller capacity. 

[Onoff]

Do unvented require an annual G3 inspection?

[Construction Channel]

Fwiw I was encouraged to go for an unvented heating system. Vented is considered old hat by my plumbing friends so to save the arguments I did as I was told. 

[ToughButterCup]

1 minute ago, Construction Channel said:

Fwiw I was encouraged to go for an unvented heating system. Vented is considered old hat by my plumbing friends so to save the arguments I did as I was told. 

 

So, what's the benefit of Unvented over Vented? Apart from the system being newer ....

[Jeremy Harris]

Unvented gives mains pressure hot water, vented gives just tank head pressure. 

 

Unvented needs a G3 installation (widely, almost universally, ignored, IMHO) if the capacity is over (I think) 15 litres, and in theory an unvented system over 15 litres is supposed to have an annual G3 inspection (again something that's pretty much universally ignored).

 

Unvented is the better system in terms of hot water delivery and energy efficiency, but does need some key safety precautions, including limiting the inlet mains water pressure (usually to around 3 bar) and having a proper pressure relief valve, visible tundish and overflow pipe.

 

 

[ProDave]

If I understand it, unvented has normal taps and can feed more than 1 tap.

 

Vented are the type that go over a sink. The outlet spout is the vent, and the tap is on the input to the heater.

 

So if you want it to be discrete and look "normal" it has to be unvented (which have a small built in expansion vessel)

[ToughButterCup]

21 minutes ago, JSHarris said:

Unvented gives mains pressure hot water, vented gives just tank head pressure. 

 

Unvented needs a G3 installation (widely, almost universally, ignored, IMHO) if the capacity is over (I think) 15 litres, and in theory an unvented system over 15 litres is supposed to have an annual G3 inspection (again something that's pretty much universally ignored.

 

Unvented is the better system in terms of hot water delivery and energy efficiency, but does need some key safety precautions, including limiting the inlet mains water pressure (usually to around 3 bar) and having a proper pressure relief valve, visible tundish and overflow pipe.

 

 

 

Thanks. 

I have 4 bar to an external tap where we live currently, so I'll have to limit the pressure somehow. 

Nuvver steep learning curve ahead, I see.

[Ed Davies]

2 hours ago, JSHarris said:

Unvented needs a G3 installation (widely, almost universally, ignored),

 

…but probably not by a BCO signing off a new build, I imagine.

[MikeSharp01]

1 hour ago, AnonymousBosch said:

I have 4 bar to an external tap where we live currently, so I'll have to limit the pressure somehow.

Pressure regulating valve is all you need to limit the pressure. £35 should cover it.

[PeterW]

18 minutes ago, MikeSharp01 said:

Pressure regulating valve is all you need to limit the pressure. £35 should cover it.

 

For an unvented appliance you need a pressure relief valve, with a blow off to an external drain point. Also wise to fit an expansion vessel.  

[ToughButterCup]

10 hours ago, PeterW said:

For an unvented appliance you need a pressure relief valve, with a blow off to an external drain point. Also wise to fit an expansion vessel.  

 

Oh yeah? 

Now you tell me  ( just in time ? )

10 hours ago, Ed Davies said:

…but probably not by a BCO signing off a new build, I imagine.

 

Thanks for watching my back.

Is there any online guidance around?

[Jeremy Harris]

13 minutes ago, AnonymousBosch said:

 

Oh yeah? 

Now you tell me  ( just in time ? )

 

Thanks for watching my back.

Is there any online guidance around?

 

 

They are often supplied with a kit that includes the pressure reducing valve and the pressure relief valve.  There may well be a thermostatic mixer valve included as well, to regulate the hot water output down if needed.

 

The pressure relief valve has to vent to a tundish and the tundish needs to be connected to a discharge pipe with specific constraints.  These are given in Part G3, ( https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/504207/BR_PDF_AD_G_2015_with_2016_amendments.pdf ) on page 24.

[ToughButterCup]

If you wanted to make a complicated, expensive, annoying system for delivering warm water, you'd invent an Unvented System, it seems.

All that spaghetti,  all those valves, all those regulations, all those regulators, tun dishes.

 

I like simplicity. Unvented isn't.  I now know why I'm not going to use an unvented system

[SteamyTea]

11 minutes ago, AnonymousBosch said:

If you wanted to make a complicated, expensive, annoying system for delivering warm water, you'd invent an Unvented System,

I disagree.

Vented is very simple.  One tank to feed the cylinder, a pipe to take the hot water away.  And one pipe back to the tank for safety. That is it.

No need for pressure reducing valves, expansion vessels, sacrificial anodes, multiple coils, maybe flat plate heat exchanges.

We seem to think that complicated is better.

[Jeremy Harris]

If you want simple for hot water then it's hard to beat a Sunamp, TBH.  JUst a cold water pipe from the supply going in and a hot water pipe coming out.  No other plumbing needed, unless you want to add a thermostatic mixer valve to reduce the hot water temperature down from the ~55°C that comes out of the Sunamp.

[SteamyTea]

2 minutes ago, JSHarris said:

No other plumbing needed,

Isn't there an overflow into a tundish, or was that just on your system?

[Jeremy Harris]

10 minutes ago, SteamyTea said:

Isn't there an overflow into a tundish, or was that just on your system?

 

No, that's been removed now, so the only plumbing on the UniQ we have is a cold water pipe going in to the unit and a hot water pipe coming out.  I added a thermostatic mixer valve to mix the hot water to the house down to about 48°C, but that was just a personal preference, as by default the Sunamp delivers hot water at about 55°C right until it's discharged.  Our's stores between 9 kWh and 10 kWh (dependent on how long since it was last charged), so about the same as a UVC of around 200 litres or so.

[ToughButterCup]

I agree @SteamyTea, but even that amount of spaghetti and infrastructure is too  'much ' for me. 

I was (am ?) looking at supplying 2 small bathroom sinks with just enough hot water, just in time. Enough to rinse yer toothbrush, wash hands and wash away the odd Daddy Long Legs.

 

Settled on this : unless the commentariat rises up in outrage, that is....

Why?

• Next to no infrastructure
• No hot water losing its precious heat all day
• I can install it

[SteamyTea]

Right, thought you were on about DHW in general.

We have a two small water heaters at work.  One is rubbish and the other one is even worse.

The instantaneous one either delivers cold water, or scolding water.  The larger one with a tank has an odd system when it vents.  About 3 minutes after use, it decided to expel water down the pipe.  This is because of expansion and over pressure.  Heatrea say it is normal, we say it is rubbish as it can leak water onto an area (it has a long pipe so we can fill sink and buckets).

 

[ToughButterCup]

3 minutes ago, SteamyTea said:

[...]

We have a two small water heaters at work.  One is rubbish and the other one is even worse.

[...]

 

Ziss is vy I em choosink ze Tchgerman Kompanie Stiebel Eltron

[joe90]

But @AnonymousBosch what are you doing fir DHW fir showers/baths?

[ToughButterCup]

Bath: 

 

1 hour ago, JSHarris said:

If you want simple for hot water then it's hard to beat a Sunamp, TBH.  JUst a cold water pipe from the supply going in and a hot water pipe coming out.  No other plumbing needed, unless you want to add a thermostatic mixer valve to reduce the hot water temperature down from the ~55°C that comes out of the Sunamp.

 

and maybe shower too.

[Dreadnaught]

At the risk of going off topic, I have wondered whether it would be feasible for SunAmp to design an electrically charged mini SunAmp with sufficient phase-change material only to heat the water contained in the pipes of a long pipe run and so give pleasingly instantaneous hot water at showers and sinks that are distant from the combi boiler or cylinder. 

[Jeremy Harris]

2 minutes ago, Dreadnaught said:

At the risk of going off topic, I have wondered whether it would be feasible for SunAmp to design an electrically charged mini SunAmp with sufficient phase-change material only to heat the water contained in the pipes of a long pipe run and so give pleasingly instantaneous hot water at showers and sinks that are distant from the combi boiler or cylinder. 

 

Got to be better than the small instant heater hand wash units, that's for sure.  My experience of those over the years at places I've worked has been like that of @SteamyTea, they are universally rubbish.

 

I suspect that the snag is that a small Sunamp would be far too costly for an application like this, as it would need the same charge control system as a big one, and I suspect that's where a fair bit of the cost is.  It may be that they just haven't thought about entering such a low selling price market yet.  I suspect that it would be possible to make a very small Sunamp, with maybe a litre or two of PCM, that would very much outperform the existing electric units.