I live in a flat and am about to have a new indirect hot water tank installed. The guy who is doing it has also fitted new taps for me throughout the flat, but the pressure of the hot water is awful. The single tap on the bath is fine but the mixers in the bathroom, kitchen and bedrooms have just a dribble of water.
I was then advised to have a megaflow fitted which would increase the flow. I am waiting for a price for this but have also heard that some taps are only suitable for high pressure systems, which may be the cause of my worries, and just fitting new taps could solve it, and save me a load of money! Also, what can I expect the megaflow unit to cost?
The Megaflo will cost about 600 quid plus whatever mark up the guy thinks he can get away with plus fitting (prob over 1000 quid in total). Although you may get slightly better flow just replacing the taps, the Megaflo is a seriously nice hot water system with fantastic performance. Compared to gravity hot water systems and combi boilers, it is on a completely different planet.
On the other hand, if you have a flat, you might just prefer a combi boiler, as it means you don't need a cylinder at all. Pretty slow on the bath, but good for showers.
Provided you have good mains pressure and flow, expect an unvented cylinder to be able to fill a bath in under 2 minutes. Showers will never be the same again.
Soon, you'll get a post from IMM advising you to get a heat bank instead. These have certain advantages and disadvantages compared to an unvented cylinder. They require the boiler to heat at a higher temperature, which is less efficient and they have lower flow rates. However, they are simpler to install and don't require the complicated safety systems that unvented cylinders need. (There are plenty more issues on both sides of that one).
- Instant high pressure hot water - When the store has reached temperature water is delivered instantly at the taps.
- High mains water pressures at up to 10 bar, compared to 3.5 bar with unvenetd cylinders.
- Very high water flow-rate - The high-end heat-banks have a flow-rate up to
45 litres/min.
- Long efficient boiler burn - Reduces boiler on-off cycling increasing efficiency, although inefficient boiler cycling is no longer a major problem with boilers with forced flues.
- Maintains optimum boiler temperature range ? using ablending valve the flow/return of the boiler can be kept to opimum mainatinaing greater effciencies. The boiler operates at optimum performance.
- Combines the output of the stored water and the boiler ? see the DPS GXV
- Cylinder may be smaller for a similar performance - smaler cylinders than unvented cylinders.
- Cylinder at low pressure - Unlike an unvented cylinder it does not store water at high pressures.
- Fast cylinder recovery rate - When the boiler is connected directly to the heat-bank, and not via an indirect coil, the recovery rate is rapid. Although in some cases a boiler may heat the heat-bank via an indirect coil, reducing the recovery rate.
- Legionella bacteria eliminated - The Legionella bacteria cannot survive in the high temperature sealed conditions of a heat-bank.
- No scale build-up in heat-bank ? Containing primary and not secondary fresh water, there is no scale build-up inside the heat-bank.
- Cold water storage eliminated - No need for cold water storage tanks.
- Solar heating storage - Water heated via solar panels may be stored in the heat-bank via a solar coil.
- Easy maintenance - If an external plate heat exchanger requires cleaning or replacing it is a matter of draining down the heat-bank, or closing isolating vales, and unscrewing the plate heat-exchanger. In some rare instances plate heat-exchangers are fitted directly inside the heat-bank preventing on-site maintenance.
- Easy to improve hot water flowrates ? By simply adding additional plate heat-exchangers in parallel, hot water flow rates may be improved. Retrofit additions are possible if extra bathrooms or showers are installed. This is impossible with unvented cylinders.
- Stored water vessel need not be cylindrical ? As no internal coil is used for hot water heat transfer the stored water vessel may be any shape, as opposed to a thermal store which has to be cylindrical for maximum efficiency. This has advantages where space is limited.
Disadvantages of Heat-Banks
- The store needs be near fully temperature to supply baths - Before any hot water is drawn off, the store must be up to temperature. Many later versions use a blending valve on the return to the boiler to ensure only up to temperature water is pumped into the store by the boiler. This prevents agitation of the stored water, and aiding heat stratification within the store giving useful water at the top of the store within a shot time. The water is heated only in one pass through the boiler.
- May not take full advantage of a condensing boiler - Maintaining the stored water at 75C to 80C results in a generally high boiler return temperature. This will not take full advantage of a condensing boiler, which increases in efficiency with lower return temperatures. With the superior heat stratification of taller cylinders this problem will be reduced. Condensing boilers with a high operational flow and return temperature differential are best suited to thermal stores and heat banks. Overall efficiency with condensing boilers is still very good.
- Lower water temperatures with fast flow-rates - As with Combi boilers, fast flow-rates through the plate heat-exchanger results in lower water temperatures. This is not so pronounced with heat-banks as with thermal-stores. This also applies to unvented cylinders and combi's. With a heat bank, extra plate heat-exchangers can be fitted to increase flow rates.
See above.
No so. They can operate up to 10 bar pressure. Unveneed cylinders can only operate up a typical 3.5 bar.
Heatrae Sadia recommend an absolute minimum 20lpm flow from your mains for the Megaflo. This is definitely on the low side of what you should be using. You are certainly limited by the maximum flow from the mains, rather than the system inside your house. As a very rough guide for the maximum flow rates for hot water you should expect for mains pressure systems:
Obviously, these will vary a lot between manufacturer and boiler power etc. However, none of these systems can provide more flow than your mains supply. If you only have 20lpm from the mains and it is not practical to upgrade the supply, then a combi might be more appropriate than an unvented cylinder (being cheaper and smaller).
Shower hoses and heads are notorious for slowing down the water. In particular, if they are designed for combi boilers, they will do their best to reduce the flow below 10 lpm for more reliable operation. It is possible to get wider bore hoses and bigger holes in the shower head if your system can provide a greater flow. If the shower head was designed for an electric shower, it would have an even slower rate.
Whilst I agree with many of the advantages, I'd say not everything is entirely true.
DPS seem to want a pressure reducing valve if static pressure is above 6 bar.
Whilst very good, unvented cylinders will supply more. (i.e. Megaflo claims
72 lpm)
A header or expansion tank is needed for the vented heat bank store. This is frequently combined with the store itself in a combination cylinder, but this requires additional head room.
Could you explain how increased flow rates decrease water temperature with an unvented cylinder? The limit on flow rate with an unvented cylinder is how much water you can shove through the thing, presuming a good design on the water inlet that doesn't unduly disturb stratification. Obviously, if you draw at 75lpm, a 150l cylinder will be cold well within 2 minutes (but then you've already filled close to 2 baths by then).
Again, the only heat bank I've got details for (DPS Pandora) claims 6 bar. However, the pressure reduction isn't as bad as it seems. Obviously, as water is drawn off, the pressure falls massively. So even if your static pressure is 6 bar, drawing 75lpm will cause the pressure to collapse below 3 bar, meaning the pressure reducing valve is fully open, and only providing a restriction in line with the reduced bore of its opening, probably equivalent to a 90 degree elbow or a few metres of pipe.
What's the reply likely to be if I call Severn Trent and ask them to turn the flow up?
'Of course, how high would you like?' 'Of course, that'll be a 50% increase on your current £90/month water bill[1]' 'Bwahahahaha'
or something else?
[1] Bit of a bugger when the meter reading sensor thingy was never actually connected to your water meter and you end up paying for three years usage in one.
20 lpm will almost certainly be within what they consider to be their contractual obligations. It is on the poor side of normal, but not as bad as some get. Your only hope is that the problem is between the street and your cylinder. Compare with other nearby houses to see if they are any better. Make sure the stop c*ck is fully open. Make sure they piped the main run to the cylinder in 22mm and your main supply to the stop c*ck in 25mm MDPE.
My fear would be, however, that the entire district suffers from low pressure, as a new house will have a new water supply anyway.
Thanks for all the advice. As I am totally non-technical some of it is a bit beyond me! However, there are a few things I should perhaps clarify.
I have a warm air heating system which was there when I moved in (almost new) which I am keeping so no chance of a combi. I have to have the cylinder changed to an indirect y-plan system so I can have rads running off, heated by the warm air unit water heater. This is ok, it's just that I have been told that a megaflow is the only way to get the hot taps running ok. I already have a nice new electric shower installed. Basically it's just 3 sinks which are suffering and so spending any more than is absolutely needed is going to be painfull! I had a quote today of about £800 (just supply) which is nowhere near what I was expecting!!
I spoke to a guy today who thought it could be the pipework which has been used to install the new sinks - the bath is ok (fills faster than any I have ever had before) and this is the original bath using the original pipework. He said hot water pipes should be 22mm, but the ones going up underneath the new sinks in my flat are 15mm. He also said flexi hoses severely reduce flow, which have been used on 2 of the sinks as far as I can see.
My guy said the bath has a better flow because it is lower down. It's only a matter of inches - can this be true? Is it possible he has used incorrect pipework and just doesn't want to admit it? When I asked him he did not know that some taps were unsuitable for gravity fed systems so the kitchen one may be useless anyway and the flow is pitiful. My mains cold water pressure is very good indeed.
Another thing is he has installed a shower for me and the outside drain became blocked and sewage came back into the shower! He admitted he hadn't installed a non-return valve as they can get blocked themselves so it's not a good idea. The drain unblocker guy said I should have had one.
Am I being taken for a ride? This is why it's great to have your advice as I would be none the wiser otherwise!!!!
It is all down to what the plate heat exchanger can take. Most are about 10 bar, max. This is another advantage in that no pressure reducer is fitted.
Just add plate heat exchangers (not very big) and it will give you more than the Megoflo as no pressure reducer is fitted.
Not an issue really.
That is true. A good heat bank with a well sized boiler can virtually heat the store faster than what is extracted. Another advantage: a directly heated bank can take any sized boiler as long as the flow and return pipes are large enough. In fact two cheapish 80,000 Btus boilers can be fitted directly to the store with their own flow and returns for a zippo heat up (A Worcester 82,000 Btus heating boiler can be had for £534.63 Including VAT each, £1065 for two. Or a Glow Worm 30HXI condensing boiler for £663.88 Including VAT each, £1328 for two). That is, if you draw off water below approx 24 litres/min, the boilers will be re-heating faster than you draw-off - great for two showers as you "never" run out of hot water. Then you can downsize the heat banks cylinder size, saving money on the store costs to compensate.
An unvented cylinder is limited by the coil size. Some unvented cylinders can take nearly 200,000 Btus of boiler heat, but they are usualy very large and very expensive.
But if you have 10 bar to spare it is not utilised. All academic, as 40 litres/min is more than adequate for most homes, filling a typical 100 litre bath with 43C water in about 2-3 mins or so, which no one would complain about.
Not so. A heat bank is cheaper and will heat up quite fast if it is connected directly (no coil) to the water heater. The rads can be run off the heat bank cylinder by having a flow and return run off the bottom of the heat bank cylinder. I assume you have a Janus water heater.
Why?
Exactly. Find what the flow problem really is. If a new cylinder is required do not go unvented Megaflo, go "integrated" heat bank. Cheaper and more efficient.
You mean over the top?
To the bath, yes.
That is correct.
If they are kinked, yes. Replace the flexible hoses with plastic pipe on one sink and see what happens.
No. That is balls.
The pipes sounds fine. It is probably the flexible hoses and/or the taps.
I had not heard of a heat bank before or had one recommended to me. The whole thing started when I asked for rads to be installed in the bedrooms off the warm air (it's a HiJan water heater). I was given various quotes, all saying they would install an indirect unit. The the megaflo was only mentioned after the tap problem started when the new sinks were put in. I have another company coming tomorrow so will ask them about this heat bank. How much could I expect to pay for this? £800 for the megaflo was way too much. I was initially told about £200 but now I realise he doesn't seem to know what he is talking about that doesn't surprise me.
Also, why did you ask why did I have an electric shower installed? Should I not have? Was there another option? my guy said I couldn't have a mixer/power shower unless I went for a combi, but I stuck to my guns as I actully like warm air and did not want to bin a nearly new unit!
This guy is passing himself as a pro and is in business. Good job he hasn't been paid for all the work.....
The Range Cylinders models are reasonable. Christian is pricing them up right now. I think he is going that way.
BTW, he has to be BBA approved to fit a Megalow. If the thing bursts, and they can really make a mess as they are at high pressure, unlike a heat bank, the insurance company will not pay out. They also require an annual service too, which the insurance company will look at too. I doubt if your man is BBA approved, or CORGI either.
He sounds silly to me. Electric is expensive to run by 3 to 4 times per kW. You already have gas so use it. Integrated power shower mixers are available, see Screwfix, and are not expensive. They give a very good shower. These have the pump in the mixer plastic cover.
Nah. I've gone for a 180 litre indirect DPS Pandora fed by a Bosch Worcester Greenstar 28HE II System installed in the loft on a Honeywell 'S' plan, zoned for water, upstairs, downstairs and conservatory. The conservatory might be wet underfloor or forced convection radiator, but haven't decided yet (or even built it). The loft is already boarded, with lighting and mounted loft ladder, so it is a practical place to put it.
My biggest fear with the heat bank is that drawing water will kill the heat stratifiction, leading to hot water reducing below 55C when there is still energy in the system. I'm hoping storing 180L at 75C will overcome any such problems. My water is hard as nails, so the removable external heat exchanger able is a big plus that can be stuffed with Viakal or replaced as required.
Heat banks have spreaders to prevent destratification. Put a phosphor descaler on your system. the plate heat exchanger resists scale as the plates bend preventing scale from building up. And as you say, you can take it out and descale it.
If the regs say an appliance must be installed by an approved fitter, NO insurance company will pay out if it goes wrong. The insurance company naturally assumes all is installed correctly by approved people. If not naturally they will not fork out. They will also want proof of an annual service too.
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