New Condensing Boiler and Shower

Hello,
I am installing/getting installed a new boiler and new bathroom with shower, and am after some advice to find my way through the miriad of possibilities. I have found lots of good advice in the archive but have some specific queries.
The existing system is a gravity system with a 25 year old boiler situated in the bathroom. It works well enough (with occasional hiccups) but I want to move it and it seems a good moment to replace it.
The house is a large 3/4 bedroom Victorian terraced house with one bathroom (shower in bath) and there are 3 residents - 2 adults, 1 child. I would like to build in capacity for an additional bathroom with shower.
I am concerned about energy consumption and cutting my fuel bills so a Condensing boiler seems the way to go.
The next question is Combination or Conventional boiler. I had a combi in my last house and liked the convenience. Against that I am concerned that the pressure I would get wouldn't be that great (a local plumber says that mains pressure is variable in the area and has dropped recently) and whether a combi would be up to the task. I have a Gravity system at the moment that works so I suppose if it aint broke don't fix it ? So Conventional boiler it is.
Reccomendations for Condensing Conventional Boilers? From searching the archive, in my budget, the Vaillant Eco range and the Keston Celsius 25 get good press. Any comments ? How do I work out what Kw rating I need for my house ?
I like a decent shower. It is good at the moment a mixer tap with a victorian rose head , giving low pressure but a flow rate of approx 20 l/min. This is achieved by a 22mm feed from hot water tank on floor above. The cold water tank is in the attic, two floors, approx 3m above the shower head.
I have been looking at thermostatic mixers and they seem to need more water pressure than that. What I don't want is to change everything and find that I have a much worse shower.
So I believe the options are low pressure thermostatic mixer, venturi shower, installing a pump or indeed a Unvented system. One by one:
Low pressure thermostatic mixer - Do they exist ? Would they just give a dribble ?
Venturi shower - Seem to be mixed feelings on these
Pump - Do I site this next to the hot water tank or by the shower ? Single ? Twin ? Negative ? Positive ? What does this all mean ? Is an integrated power shower a better idea? Could it pump water for possible second bathroom too.
Unvented system - What pressure would this actually give ? Same as mains in which case similar problems to Combi ? Pipe from street is 15mm, upgrading is possible, is it effective ? very expensive ?
Also any reccomendations on shower fittings ? Looking at Hansgrohe, Mira, Grohe, Aqualisa.
Apologies for length of query, just trying to give all the info. All help much appreciated.
Bjorn Ventris (Remove the NOSPAM).
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They exist. Not a dribble, but not startling either.

Get a good and make sure it works on the correct mains pressure.

Wherever convenient.

A twin. One hot one cold. The hot from the top of the cylinder using a Surrey flange and cold off the tank in the loft.

Unvented cylinders are pressure reduced to approx 3.5 bar for steel and 2 bar copper. A combi is not reduced. A heat bank is a far better solution than an unvented cylinder.

Any good one.
You say you are keeping the existing gravity fed system with a tank in the loft. If the tank is fine then keep it. Replace the cylinder with a quick recovery model. Try the Telford Typhoon 115 litre model as it will do two bathrooms when the boiler is set to max and using a priority system. The problem now is the high pressure shower. So get a condensing combi and use the water section for showers only. The Ideal Icos is good, and sabout the same price as the eqiv system boiler. http://www.discountedheating.co.uk/shop/acatalog / This eliminates a power shower pump. A good pump is 200-250, so the combi ways is the best and no vibrations and noise. Have the CH side of the boiler act as a normal CH/DHW (cylinder) system.
If the tank has to go then consider a combi cylinder with a quick recovery coil of 115 litres hot and 115 litres cold. See Telford, who will make one to suit as will Range. http://www.telford-group.com/trident.htm http://www.range-cylinders.co.uk
Many other cylinder makers may help you.
A combi cylinder can go in the airing cupboard and eliminate the cold tank in the loft, or go in the loft and liberate an airing cupboard.
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Thanks for the advice, but what's a heat bank ? Quick recovery hot water tank sounds like the way to go. You reccomend Telford ?
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See: http://www.heatweb.com They will explain.

Good and cheap, from Travis Perkins. See Albion which will guide you on sizing. http://www.albion-online.co.uk Quick recovery cylinder using a priority system (3-way diverter valve) can mean the cyoinder is downsized to 80 litres from say 114 litres.
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This is a nice theory, but I am not convinced that it would be as good as you describe. You are talking about a 20 degree rise at 15 litres per minute. That needs just over half the energy that a combi would require at similar volume (about 21kW, as I calculate it). Getting that through a heat exchanger made of MDPE pipe when the heat source (i.e. the floor) is not that much warmer is not very plausible. It would need a very long length of pipe and that would add problems with flow resistance.

Provided that the cylinder is large enough, which takes us back to the point that it is only as good as the energy stored plus the energy that can be delivered into the heatbank from the boiler while the former is delivering energy to the heat exchanger.

It's easy enough to calculate that when comparing a heatbank at 76 degrees with a conventional cylinder at 60 degrees.
For the same amount of stored energy, the height of the cylinder could be reduced by 60/76. For a 1500mm high cylinder that would be to 1185mm approx. - a saving of 315mm - about a foot. Enough space to put a couple of pairs of shoes. Hmmmm. Not a decision making criterion that seems that big an issue unless you are in a small flat.

This isn't really relevant because the flow rate through a combi is the key issue, not the pressure that it will withstand. Pressure and flow control is required on most mains fed systems anyway, regardless of technology, in order to balance the flows of hot and cold to a reasonable extent.

200 litres is not particularly large and could not be substantially reduced by the use of heatbank technology as already illustrated.

That depends on the cylinder design and specifically the heating coil.

In fact I could since the cylinder has plenty of connection points. I am also quite impressed with the Swedish made GEA Ecobraze heat exchangers - the one I have for the workshop circuit performs very well.
However, the match of a direct heatbank to a more sophisticated condensing boiler is not a good one, and this does not leave any significant advantages for the heat bank, unless one is really tight on space.
.andy
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MDPE? You can use two way santoprene pipe. This is 2 or 3 way counter feed pipe. Mains water in one way hot water in the other. Running PEX side by side is good enough. Many in the USA have done this and reported good results.
The USA has different water regs to use. They use a hot water cylinder and take off fresh water and run it through a non-ferrous UFH system. Many companies run cold mains water through the same pipe loop by turning a manual 3-way valve to cool the floor in summer.

No. The system acts like a combi as a fall back.

And millions are.

Combi??
It could. Store water at 80C and have a large output boiler to assist when drawing hot water.

Yes, and unvented cylinders do not have very large coils.

Those sold by DPS are about the best. I forget right now who makes them, but they are about the most efficient and not expensive.

A smart condenser will work well with a heat bank. A heat bank with the top half at 76-80C for DHW and the bottom at 45C for UFH works very well with condensers. A diverter valve sends the boilers output to either section.
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Fine, but probably not applicable here. SInce most houses in the U.S. have timber floors, I wonder where this is used.

Sure, but the performance level will have dropped off.

.. and millions are not. Either way, I don't see this as a major selling point. Minor one maybe.

The net equation is still the same. It doesn't matter whether the boiler is providing the energy via a conventional cylinder or a heatbank. Once the stored energy is used up, both arrangements fall back to combi behaviour. The only real difference is that in the heatbank case you have stored 25% more energy in a given volume or a small reduction in space.
Sorry, but I don't think it's that big a deal.

Looking at the pictures, it looks as though these are the ones that they carry.

We've already had this discussion and I illustrated why this would not be the case. I'm not going to go over the same ground again.

.andy
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wrote:

It was used in a concrete floor.

The point is you "never" run out of hot water. Your hot water is 2 stage of high flow and then low flow.

Few British house have space to spare, hence combi boilers account for 60-70% of the one million boilers sold each year.

It was about unvented cylinders, heat banks.

No. With a beat bank the boioers output goes straiught to the DHW draw off. This si noit the case with a vented or unvented cylinder.

You don't understand.

Again.. unvented cylinders do not have very large coils.

You don't understand.
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Hmmm.
That's fine if you find that type of performance acceptable. My point was to highlight that this low flow situation would happen.
I would prefer to see the cylinder adequately sized regardless of whether it is used in a conventional way or as a heatbank.

I don't think that you can deduce that as a causal connection, merely as a contributing factor. Others are that to an extent, a combi installation may take some time cost out of installation in new builds. In terms of replacements, if the water supply and appliance size are inadequate, we have an unhappy customer since they have bought a 21st century version of the geyser.

I said any system using mains fed hot water as opposed to a roof tank.

No it doesn't. With a vented or unvented cylinder, the boiler energy is fed through a coil in the cylinder to heat the DHW in the cylinder. A heatbank can be indirect or direct. In the indirect case, the boiler heats a coil in the cylinder in the same way, but the water is then pumped through a stainless steel heat exchanger to heat the DHW. In the direct case the cylinder water passes through the boiler but is still used via the stainless steel heat exchanger to heat the DHW.
.

I understand perfectly, thanks.

Rubbish. If you order one with a substantial coil, you get one with a substantial coil. That's exactly what I did. I had the manufacturer install a pocket for a temperature probe and extra fittings as well.

Sorry to burst your bubble, but I understand completely.

.andy
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Just about everyone with common sense would find it acceptable. You have enough high flow water, then if you do run out of high flow your fallback to a low flow. Never run out.

What makes you think it would not provide enough hot water?

failed!
You don't. failed!

Coils in unvented cylinder are never as large as vented because if a large boiler heated up the cylinder from cold it would create too much pressure in the cylinder and the pressure relief controls would cut in. The Telford Tornado is "trickle" charged.
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I have simply related what I know to be the case because I have done it.
.andy
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wrote:

You haven't done it. You don't have a heat bank!! Gosh!!
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well know.
It is quite possible to order a pressurised type of cylinder with a fast recovery heat exchanger . I have done that. Would you like me to email you the receipt?
Do you have a heatbank, BTW?
.andy
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(Bjorn) wrote:

How big is your hot water tank ? Who makes it ? How much ?
Bjorn
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snipped-for-privacy@blueyonder.co.uk (Bjorn) wrote:

As far as I can remember it was about £150. It is 200l (bigger than usual as I have a very big bath which takes 250 liters to fill up.) I con fess that it is just a new ordinary lagged copper cylinder, and performs to part L and is a quickish recovery cylinder. Which is better than the older cylinders but still not as good as some more expensive suggestions that come up here. It works for me. I have never run out of water and the shower eats it up at 20l a min output. You could get a calculator out and work out the math and determine that a very quick recovery cylinder would do for you and take up less room, but they are more expensive. My cylinder is the same width as the old one, just a few inches taller, so why waste the money IMHO unless space is a premium.
Richard
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(Bjorn) wrote:

It is not quick recovery. It is a standard cylinder. Part L is the new better standard. With a quick recovery you could have got away with a 150 litre cylinder and maybe a 125. Quick recovery are cheaper to run as the boiler is operating more efficiently.

The Telford Typhoons are not expensive at all.

You have to understand what a quick recovery gives you. I cannot see the need to fit Part Ls.
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Why don't you read before you ramble. I said it was NOT a quick recovery cylinder, just better than the old ones. Anyway does it really matter if I can 'get away' with a 150l or 125l if I have the cupboard space going begging. Further if I fill a 250 litre bath with taps full on, do I really have enough hot water in 125l Richard
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THat's rubbish as well. The heat loss through even a standard Part L cylinder is de minimis. The difference between a 150 litre and, say, a 200litre is not even worth discussing.

.andy
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wrote:

Although less standing heat losses, no one is on about this point. A quick recovery rakes all the boilers heat with boiler cycling.
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80 litres will do for a quick recovery to replace the 117 litre British Standard. Telford Typhoon is 100 from Travis Perkins. A good deal. http://www.telford-group.com/typhoon.htm

If you insist on a pump (poor move) then you should go for the up market brands. Cheap pumps can't hack it. For e.g., a Stuart Turner will be 200-250 plus fittings, surrey flange etc. Consider getting a combi and running your shower only through the combi water section to give high pressure showers, and on the heating side of the combi treat as a normal system boiler. This way, no noisy vibrating pump and cheaper into the bargain too. BTW, I am no DIYer, take what I say very seriously.

I have and they are very good.
From Discounted web site. As you see there is no difference between the combi and the system boilers in price.
Ideal Icos M3080 System Boiler Fan Flued System Condensing Boiler.
BTU's - 30 - 80,000
685mm High 390mm Wide 278mm Deep
Price Includes Flue & Delivery.
Price ex VAT: 630.00 740.25 Including VAT at 17.5%
Ideal Isar Price Includes Boiler - Flue Kit - Delivery
Fan Flued Condensing Combination Boiler.
The Isar is an automatically controlled, fanned flue high-efficiency boiler. The boiler modulates its heat to suit the demands of the heating load, it incorporates the variable thermostat for centeral heating temperature control, adjustable from 50 to 82C. The use of the pre-mix burner allows control of gas input to the appliance to be directly linked to the fan speen. So, as the reduces speed to match heating load, the gas valve maintains the corrcet proportional flow ensuring a high boiler efficiency throughout its output range.
Output - 30,000 - 100,000 BTU's (8.9 - 29.3kW)
Compact Dimensions:- 685mm High 390mm Wide 278mm Deep
Flue Diameter - 100mm
Max Lift Weight - 43kg
Price ex VAT: 630.00 740.25 Including VAT at 17.5%
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