Central Heating Prefabrication - e.g. DPS

[Stephen Fasham]

I need to completely redo the plumbing and heating in my house (current 55kBTu Potterton only heats half the rooms and the smallest hot water tank I've ever seen). I haven't done accurate calcs yet but a rough estimate is that I need about 130kBTU to cover HW and CH. I know basically what I want to do, which is: Boiler - Keston C40 condensing 130kBTu (this was even recommended by the plumber who came to fix the gas leak on the current set-up - a plumber recommending a condensing boiler - whatever next!) CH - 4 zones (4 storey house) each controlled by digital room stat to

2 port valve. Regarding this, does anyone have experience of modulating pumps, the plumber (see above) recommended just fitting a big enough shunt pump and letting the automatic bypass deal with excess flow in the situation where the heating demand isn't very high. HW - this is where I'm not sure about a Megaflo unvented cylinder or a Heatbank and would like some advice.

However I would like to get the central components pre-fabricated i.e. boiler, tank and control valves to make installation easier. It is all to fit in an airing cupboard but I do have 9'6" ceilings so there should be plenty of room. Does anyone know of companies that offer this other than DPS, and if not are they as good/affordable as they claim. I am quite happy to do all the rad runs and feeds etc. Having done my own system last time (open vented with fanned flue boiler) I'm sure I could manage the design for the whole lot, but if the cost of getting it supplied ready wired is not much, the time saved would be welcome.

All advice gratefully received.

Stephen

[Alex]

Have you thought possibly about a Potterton Powermax? (apparently much better than the usual Potterton offerings).

Alex

[Andy Hall]

Keston do combined rigs of boiler and cylinder system but you pay for the privilege.

Albion do a range of heatbanks as packages......

I'm not sure that the C40 modulates the pump - the Celsius does, but only to three settings IIRC. However that is only 25kW.

The MAN Micromat that I have has a modulated pump which goes linearly from 20-100% of flow controlled by the boiler's microprocessor. You can get versions of this product up to 76kW so 40kW is no problem.

Alternatively, you can use an external pump like a Grundfos Alpha which will also modulate based on the resistance to flow. The boiler would then adjust accordingly.

With a modulating boiler, the power output will be reduced anyway as TRVs and zones close or reduce. With separate zones, it is conventional to arrange a switched live from each zone valve to the boiler demand. Thus if any are open, boiler fires, all closed and it doesn't for heating purposes.

.andy

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[MIKE THORNE]

As a plumber I don't know about prefab pipe-work but the Keston C40 System boiler has a modulating pump inside, it's a very nice boiler but with a very nasty price. Go with the above boiler and mega-flow and use TRVs no need for all that zoning.

[IMM]

Don't say it loud.

Zoning is easy to do. You can knock off 15-20% of your heating bill by not heating upstairs when no one is there, which is most of the time during the day.

[Ed Sirett]

I have fitted 1 C40 and a few C25s. The C40 does modulate the pump (3 speeds IIRC) and is essentially the same design as a C25 but bigger. It has two independant demand inputs (intended so that the space heating can be adjusted independantly form the DHW heating). The C40 was coupled to an Albion unvented.

You can add external weather compensation essentially it's a thermistor in a round electrical plastic box. There was only one problem which I had which was directly to do with Keston which was that after adding the weather comp I could not get the rads hot enough to heat the house. However Keston intructed me how to alter the boiler parameters to allow the boiler to work with existing 75C nominal radiators and the compensator.

Since the C40 is the best part of £1500 - trade. I would also look to see what MAN Micromat have to offer.

You'll need to supply the boiler form 28mm/1" gas pipe unless the meter is directly under the boiler.

I'd strongly argue for zoning the house with any number of 2-port valves + a HW zone that uses the other boiler control knob.

But still use TRVs and also you'll need a small (bathroom?) rad for a permanent bypass to comply with the installation instructions.

[IMM]

Albion do thermal stores not heat banks. A heat bank has a plate heat exchanger, while a thermal store has an internal coil for for DHW take off. Terminology is settling down to this explanation, but not quite as Range do "heat banks" yet refer to them as thermals stores. I think they are about the only company that does.

They are both of a similar operational principle but a heat bank is more efficient and can give hot water when only the top half of the cylinder is hot. A thermal store needs most of the cylinder heated before any water of a meaningful temperature is drawn off.

[IMM]

This sounds like a case of buying two smaller £700 condensing boilers like the Glow Worm or Ideal ICOS. Use a "directly" heated DPS heat bank and have the two boilers heat the store. Being direct the heat bank will take all the heat the two boilers will throw at it, re-heating pronto. Make sure the heat banks boiler tappings are at least 28mm, or have two sets and have the two boilers heating the heat bank directly. Also built-in redundancy. One boiler drops out one will work.

I would also upgrade the loft insulation, draft proofing etc, and re-calculate the heat requirements. The boiler(s) may not need to be so big. But using a directly heated heat bank, the boiler size doesn't matter if it or they, are oversized. An oversized boiler directly onto rads will cycle, while on a heat bank it will just re-heat faster. Also a fast re-heat, using a larger boiler(s) means the heat bank is essential larger for DHW purposes.

You can use most of the gas energy available to you via the gas main, which few ever do, and have fast re-heats and a much smaller cylinder, or a very large cylinder taking more space and a smaller boiler. I prefer in general to have two smaller boilers and a smaller cylinder. Much better all around.

[IMM]

Many think the boiler sits there giving out two temperatures via two different flow pipes. If only. One for DHW and one for CH (say low temp UFH). It does not. The boiler has two stats and one flow and one return pipe. The DHW takes priority, in that if a signal from DHW is received by the boiler it runs up to the temp set on the DHW stat, when DHW is satisfied and the signal ceases, it then reverts back to the lower CH stat temp.

If UFH is run directly from the boiler, then it would run up DHW temp if DHW is called. When running UFH directly from the boiler, not via a blending valve, it is best to have a 3-way valve on DHW priority. When DHW is called very hot water goes to the cylinder only. The cylinder should be a quick recovery cylinder. When the boiler reverts back to UFH, it will be at a lower temperature dictated by the outside weather compensator.

I once installed two boiler stats on an old Glow Worm boiler eons ago.

[MIKE THORNE]

room stat also stops the boiler cycling and stops the bathroom becoming a sauna in the summer, just my opinion.

[IMM]

Good approach.

I fitted an Ideal boiler for a relative. The boiler had a fault from new and I called out the Ideal serviceman (I don't call servicemen engineers). He changed the fan motor. The problem persisted. I called them again. This time the serviceman changed the motor control board, which was the problem, but logical deduction meant it was the only thing left to change. He then looked around the system (this was a boiler change; conventional to combi) and noticed new TRVs on all the rads except the one in the hall where the wall stat was. He said the bathroom radiator should not have a TRV on. I said the hall rad acts as the bypass rad and there is a lockshield on both pipes. He kept on about having the bathroom rad with a TRV, as "we always have the bathroom rad without one". I explained to him that the hall rad was much larger thatn the bathroom rad and further away, and when the pump operates to get rid of excess heat the heat doesn't actually reach the rad, and that the large hall rad will give more than enough flow of water through the boilers heat exchanger.

He kept on about having the bathroom rad without a TRV. By now I was getting irritated by this idiot. I asked him if a bathroom has some sort of magic karma in there compared to a hall, that works its way inside the rad to the water. He said he will have to make a note in his report that the bathroom rad was not fully open at all the time. I said make sure you mention that the hall rad is fully open all the time too.

This idiot of know-it-all then said the wall stat in the hall was opposite the hall rad, which it is, and that the hall would heat up before the rest of the house and switch it all off as the stat was too near the rad. I pointed out that heat from the rad would rise up to the ceiling then up into the stairwell to the hall space on the 1st floor, and if the heating was dropping out prematurely they only had to raise the stat temperature setting until the optimum is found, and that they will do this by trial and error as most people do. I said to him you need to understand how heating systems work.

[MIKE THORNE]

Well done. You should apply for his job, or at least his wages.

[imm]

In message , IMM writes

So you managed to knacker the fan and pcb ... well done

[Stephen Fasham]

The purchase price is not the most important factor given that my gas bill at the moment is ~£90/month and as I said the heating only covers half of the house. I was planning to fit TRVs but the idea of the zoning was that the house is very large (but cheap due to the amount of work - oh and the shop that I need to get change of use for) so I don't want to heat the bedroom floors during the day, particularly since the only floor that will be well insulated is the top floor (once I've added all the celotex). This is also the reason for using digital roomstats, so that I can keep the unoccupied areas from getting too cold. For example I'm hoping that say the top floor stat is set to 16C then this will drop out before the TRVs so shutting off demand from this zone until it cools down too far. The house is mostly stone and so is lousy from an insulation point of view, but acts as a large heat store so it's best not to let it get too cold.

Anyway, any testimonials from people who have used DPS??

Stephen

PS What is the obsesson with the 'two boiler solution'?!

[Andy Hall]

Don't worry, Stephen, he can't help it.

Come May, there'll be another solution. Last month's was two multipoint water heaters used to heat thermal stores.

.andy

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[IMM]

engineers).

Maxie, all broke out of the box. Well they fan wasn't, they thought it was.

[IMM]

They are good, and will custom to order.

Obsession? Two smaller boilers are cheaper than one big one. If one boiler drops out you are down. With two one will still work. A win, win, situation.

[IMM]

Andy, different solutions to different problems. It may a shock to you, but all houses are not the same as yours.

[geoff]

In message , IMM writes

That's what they all say ...

[Andy Hall]

during different months.......

Mmm I know.

.andy

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