Advantage of unvented cylinder outweigh the disadvantages?

[Ric2013]

I have come to my decision I might as well do my G3, even if only for maintenance jobs.

Question I have is WHY we are fitting so many of these unvented cylinders i.e. 27 gallons /117l size or above (I'm not disputing the need for 10l unvented 'cylinders').

They 'need' annual servicing by a G3 plumber. That represents a cost. While my father had a kind of unvented cylinder that could expand back up the main and also had an incorporated air bubble that gave nearly 50 years of service with no maintenance whatsoever, it also had no safety devices to go wrong. 1970s 'Hoval' boilers seem to be better quality than modern UK unvented cylinders which are unlikely to have the same lifespan, and, for safety's sake, most of us agree maintenance is vital. But the inherent cost of having that done pits money vs safety. This does not happen with vented cylinders which only 'need' annual cistern cleaning which is well within the realm of a skilled DIYer and it is harder to argue that there is as concrete a danger from an uncleaned cistern as there is from an unmaintained cylinder.

They cost more to purchase. I'm not sure they don't cost more than a vented cylinder AND a shower pump.

They need a good mains supply. I am on a shared 1/2" pipe with the neighbour. If I wanted an unvented cylinder, that would entail a new water main. In any case, flow would be limited to whatever the main could provide. My bath tap gives around 22 l/m using gravity with about 0.2m standing pressure. Or I could pump the water. I couldn't do that with an unvented cylinder.

Most houses have space for a cylinder feed cistern, even if only the space directly above the vented cylinder.

I suppose they save on installation cost.

So what am I missing, except the chance to use weird European small-bore taps that won't be needed/available once we complete the project of alienating the rest of Europe? There must be some significant advantage in having unvented cylinders! Or are they just the 21st century version of Primatic cylinders: easy to install?

 

[Chuck]

If you want nice showers, and these days a lot of people do, then unvented is beneficial.

The question I have about the spread of unvented systems relates to the capacity of the water distribution network. Until around 1980 pretty much every home had its own CW store that acted as a buffer at times of peak consumption. Water mains and service pipes were sized accordingly. As more and more homes convert to unvented systems I think that the mains are going to struggle to meet demand and delivery pressures and flow rates are going to drop towards the legal minima, which are too low for unvented systems.

 

[Ric2013]

If you want nice showers, and these days a lot of people do, then unvented is beneficial.

The question I have about the spread of unvented systems relates to the capacity of the water distribution network. Until around 1980 pretty much every home had its own CW store that acted as a buffer at times of peak consumption. Water mains and service pipes were sized accordingly. As more and more homes convert to unvented systems I think that the mains are going to struggle to meet demand and delivery pressures and flow rates are going to drop towards the legal minima, which are too low for unvented systems.

I think we're on the same page then, Chuck.

Even with a shower, you're stuck with what the mains can offer. I was at a property just yesterday and I was testing the mains pressure purely as a matter of interest. Nearly 4 bar standing pressure, but only 13lpm at an outside tap (did not test working pressure but the flow suggests the working pressure may be a tad lower). And that was in the afternoon, at an off-peak period of the day.

13lpm would be a very good shower, but that's before you consider the loss of head through a shower mixer vs the relative lack of loss through the outside tap arrangement. Realistically, 6lpm is a perfectly decent shower and anything above 4 is acceptable in my book, but compared with a power shower that delivers 14lpm, I'm wondering how the unvented cylinder truly has the edge over a good combi boiler. (A Vitodens 200 can provide the 14lpm (DT 30), so, on a good mains, it would be just as good as a power shower, for example).