CH+HW upgrade, unvented or thermal store cylinder?

[Ian Calderbank]

Dear all, I'm looking to get the GFCH system upgraded on a large 4/5 bed 1970's detached house we just moved into last winter. The boiler is an almost new (recent replacement by previous owner) potterton kingfisher

80BTU so that won't be changing any time soon. A key goal is to have a substantial volume mains pressure (which is pretty good) hot water supply for the bathroom (2x) refurbs that are the next job along the line... existing cylinder is an old (and fairly small) vented indirect header tank fed which takes forever to reheat, so it goes, along with changing the pumping layout to something sensible. The airing cupboard is huge though. I can't diy this as I'm too busy at work and its too big a job (3 new rads, TRV's all round - 16 rads in total, new cylinder, new piping runs between boiler in kitchen and airing cupboard upstairs, changing pumping layout which is also a bit weird (some dual pump + flow check valve bodge onto gravity system we think).

the debates that I'm having are mainly around the cylinder selection. All the local heating engineers (the ones that want to turn up and quote that is) have a default recommendation of Heatrae Sadia Megaflo. Whilst I'm sure this is a decent product I want to look at a few alternatives, including the possiblity of a non-pressurised option such as a thermal store, avoiding the need for safety relief, outflow pipes, etc, and to have something that an unqualified person (i.e. me) can work on in the future. also I have read on various websites discussing the different system types about requiring building regs and annual inspections for unvented cylinders, is this true? I also _might_ look at adding solar hw heating to the system at some point in the future (no decisions made on that score though), so I'd like to avoid doing anything that would preclude that option, the HS site suggests this may not be the easiest thing to do with their product.

I'm found a bunch of info about various unvented/heatbank/thermal store products on the web, but as I said the local heating engineers all want to do megaflo, what I'm really after is any unbiased experience of the different types to be able to make an informed decision, so any help is appreciated.

Lastly, I am in Milton Keynes area which is ultra-hard water, so its been suggested to look at electronic scale inhibitors, any good/bad stories in this area?

any trade on here who want to contact me directly by email please feel free to do so.

thanks in advance, Ian

-- ian_calderbank at dont-spam-me.hotmail.com

[Grunff]

I have a FlowMax thermal store, which I installed after having one at our last house. I'm very happy with its performance, and intend to carry on using thermal stores for a long time to come.

By all means look at them, but don't actually buy one. Looking at them is just as effective at inhibiting scale formation as fitting one, but a lot cheaper.

[IMM]

Go for a heat bank. The local plumbers fit megaflows because they know no different. A heat bank requires an electrical connection so they shy away. A Megaflow requires you to service it each year to reinstate the air pocket (PITA). They require large 1" copper overflows too. If there is a burst the insurance will not pay up.

Get a heat bank with a solar coil already in the bottom, ready for connection. Also have the CH fed from the heat bank too. Then solar heated water will supply the CH as well as DHW. Most makers will supply a "integrated" (CH & DHW) heat bank.

(go thermal storage) Contact the makers and they will identify a model for you. DPS make heat banks that don't require an overflow.

If these plumbers say heat banks are no good they are not worth employing as they don't know their stuff. They are superior to unvented cylinders in most points, and especially when you are incorporating solar panels.

Scale? Fit a phosphor de-scaler, available from, B&Q and the lies for around £45-50, on all the water except the kitchen drinking tap and garden hose. A heat bank can be DIY descaled by removing the plate heat exchanger. Make sure they incorporate full bore isolation valves either side of the plate to remove the plate heat exchanger without a drain down and re-fill which can be expensive as they require about 3 bottles of inhibitor.

[IMM]

Flowmax is made by range cylinders. They will fit solar coils if requested too.

I'm surprised they never insulted you by saying MK is a shit hole. As that is what most of them have been saying on this ng.

BTW, use a "directly" heated heat bank, not heated via an intermediate coil.

[Grunff]

They're very helpful people IME.

If adding a solar component later, it's probably a lot easier to so it with an external heat exchanger rather than a coil.

Hey, right again! That's twice in the same post. Drugs started working?

[IMM]

Having the solar coil at the botom of the cylinder reat to be connected is the best way. It doesn't take up much space either.

They must be. Keep taking them. Well not quite, you screwed on the solar addition part. Can you take a stronger dose?

[Ian Calderbank]

well, I've spoken to Range and DPS, interestingly I got opposing stories....

range talked about both but preferred to recommend unvented cylinder (tribune) as this can come with dual coils as standard, saying service requirement was simply a matter of a pressure check with a car-tyre pressure gauge, and a test of the relief valve you can do yourself, vs flowmax with a 2nd coil would be a special build and in their opinion not as well suited to providing the volumes needed for a large house, more designed for new-build smaller homes, and also not so good for hard water area.....

DPS on the other hand straightaway suggested their heatbank, and it certainly seems to eliminate a lot of the pressure/temperature relief requirements of the unvented.

With the heatbank, the option for heating the store itself is direct onto the CH circuit or indirect via coil, the difference being whether the CH system is sealed(=>indirect) or unsealed (=>direct), at the moment its unsealed (good old feed-expansion tank in the loft which I want rid of but there is room for one in the airing cupboard along with a big cylinder), boiler capable of running either way, I have no strong preference, any pros/cons in each direction?

one interesting point between the two is the temp requirement for the stored water. 60 degrees in unvented, 75 degrees in the heatbank. So I would guess that as a possible solar input also has to heat-exchange into the tank, the lower temp would be easier to make use of that energy? But I do like the sound of not having all that pressure stuff to worry about....

neither had any suggestions about who to use for system design/install other than IOP listed (which I am trying to stick with anyway). So I guess I will just have to wave the names under peoples noses and see what reaction I get....

ta, Ian

[IMM]

Still a service. If you did it yourself and there was a burst, would the insurance company pay up? I doubt it,as they will find any excuse not to pay.

Range are big and want to sell off the shelf stock. Their FloMax is geared towards smaller homes.

An unvented cylinder will not use solar heated water for CH, it is only used for DHW. Scale? "Always" fit a phosphor scale reducer in any hard water area on any system.

It eliminates all of it as it is at low pressure

Heat banks come mainly wit the F&E tank integrated with the cylinder.

With a direct heat bank keep it the open vented. the heat bank provides the CH F&E tank.

The heat bank uses the hot water to instantly heat the incoming cold mains water. the unvented cylinder is the water you use at the taps. the water in a heat bank is primary water.

Having a solar coil at the bottom of a heat bank will heat the water in the cylinder. Fully in summer, not so much in winter. In winter it may only be tow temp, but it is being used to preheat the cylinder, it all counts and it is used for CH and DHW.

If you have ever seen they aftermath of an exploded unvented cylinder you would shy away. Total devastation.

A heat bank can have all the controls, pumps etc all on the cyinder, DPS would do this for you. All yu do is connect up the relevant wires and pipes. The flow and return of the CH circuit is connected up to the CH tappings. The DHW is a matter of cold in hot out pipes, and the boiler is a matter of connecting up the boiler flow and return to the heat bank. Simple stuff, no real design work for an dumb installer to do, and the experts who design the heat bank do virtually all of it for you.

A heat bank eliminates inefficient boiler cycling, which an unvented cylinder will not. Eventually I would replace that cast iron boiler. Modern "heating" condensing boilers are far more efficient.

If you want to replace it now then consider a Powermax or Gledhill Gulfstream 2000, which incorporate incondesning boilers. An all in one solution. The 2000 is available from Travis Perkins plumbing dept.

[Ed Sirett]

Take a look at the sealed CH system FAQ. It may well be better to heat the heat bank indirectly from a sealed system. The heat bank water itself beeing a simple F+E header tank.

[IMM]

It may be, but in this case I can't see that it is beneficial. The boiler is cast iron and open vented. I see no reason why just the boiler and the flow and returns to the heat bank would need to be pressurised. If installing a high efficiency boiler that can only be pressurised then I could see why.

[Ian Calderbank]

yes, I'd read all the faq's many times. I just had another chap round, he made what seemed like a good negative point against sealed versus unsealed

- heating installation is 30 yrs old, mid 70's house, system definately never been u/g'ed and there are several rads with cold lower sections downstairs so I'm sure its got sludge in, and all the heating pipework downstairs is buried in screed floors

- if there is any leakage, sealing/pressurising the CH circuit will only make it more so, and as most of its buried, it'll be a complete

**** to find...

and he was at least aware of the existence of thermal store/heat banks, but he said he had to go away and do some reading up before recommending options..

Ian

[IMM]

If he has to read up on it I would take his recommendations with a pinch of salt. Tell us what he recommends.

[:::Jerry::::]

So you were born with all your knowledge then - some how that figures !...

[IMM]

Pressurised thermal store/heat banks are available. These have the sealed primary flow and return from the boiler directly connected to the cylinder. They are basically grade 1 cylinders which are rated at 2.5 bar working pressure and a test pressure 1 bar above that. When used as a thermal store/heat bank connected to the boiler they operate at approx 1.5 bar working pressure and a blow valve of 3 bar, so well within range. The makers tend to stipulate that the thermal store/heat bank has its own blow off valve as well as the boiler.

I would rather go with one of these than a thermal store/heat bank using a an intermediate primary heating coil.

[Geosolar Heating]

At the risk of being associated with 'dumb plumbers' I'll give my reasons for recommending an unvented cylinder rather than a thermal store. I've got nothing against the technology of a thermal store but personally feel its had its day now that condensing boilers will soon be mandatory to the mass market.

I agree that an unvented cylinder must be installed by a trained person. IMM says that UV cyls can explode and while true it is rare due to the safety features that are mandatory. UK regulations are lot stricter than many countries were UV cyls have been the norm for many years.

To the points in question;

1. Reinstating the air bubble in a megaflow is not a difficult task.

1. 1" copper overflows are not required unless the route to discharge is extraordinarly long. The tundish has a 22mm output and this is sufficient for most installations. However, the discharge pipework must not be plastic.

2. KISS. Which is easier to understand; the UV cyl or a heatbank?

1. Solar. As far as I know OSO and Viessmann are the only UV cyls to have dual coil models. Yes, the solar won't heat your radiators, but since solar systems are designed to work at their peak in summer, surely this a moot point?

2. condensing boilers. I commented this elsewhere in the NG. UV cyls are a better option with a condensing boiler. With inefficient boilers there is no such choice between an uv cyl and heatbank.

1. DIY. Yes I'll agree that a heatbank can be DIY-ed. This suggests the owner has some interest in the heatbank technology, which is fair enough. Future owners may not be so inclined. Still, future employment for 'plumbers' when the next owners rip it out to put a megaflow in?

2. The marque. A 'Megaflow' has become something of a must-have. Probably due to marketing and keeping up with the Jones. Still, the educated customer wins out. It may be a plus-point on a future house sale.

1. Boiler cycling. Any system is susceptable to this if badly installed. I've not seen a modern UV cylinder which causes the boiler to cycle before it reaches the desired temperature. I only install the keston celsius 25, which has some features to avoid cycling.

2. All in one packages. Not something I go for myself but just a personal choice. There are equally valid pros/cons for this type of unit.

Martyn