Most powerful combi boiler

What's the most powerful combi you can get? I haven't seen much above

35kw.

M.

Reply to
Markus Splenius
Loading thread data ...

Reply to
MrBlueSkye

"Markus Splenius" wrote in message news: snipped-for-privacy@4ax.com...

What do you mean in power? The flowrate?

Here is a run down on combi's:

Firstly, a combi is a "combination" of the heating and water system in one case, eliminating external tanks and cylinders, and generally supply hot water at high main pressure. To confuse a little, some can run at very low pressures and even off tanks. Generally most are fed from the mains. It is generally a matter of mounting the boiler and connect up the pipes. The expert designers have done the hard work for you and put all in one case.

Types of combi:

1) The Infinitely Continuous Combi -

Heats cold mains water instantly as it runs through the combi. It never runs out of hot water. This is the most common type of combi, generally having lower flowrates than Nos 2 & 3 below. The largest flow rate instant combi is a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is very economical too.

formatting link
Unvented Cylinder Combi -

An unvented cylinder is a similar to a conventional cylinder but run off the high-pressure cold mains. A combi with an integral unvented cylinder has approx 60 litre cylinder heated to approx 80C, with a quick recovery coil that takes all the boilers output. A fast acting cylinder thermostat ensures the boiler pumps heat into the cylinder ASAP with a recovery rate from cold around 5-8 mins (Ariston claim 8 mins). The 80C water is blended down to about 45-50C. e.g's, Ariston Genus 27 Plus, Glow Worm, Powermax, Alpha CB50.

3) Infinately Continuous/Unvented cylinder combi -

An example being the Alpha CB50, a combination of both having a two stage flowrate, of high flowrate when using the stored water with an automatic flow regulator switching in to reduce flow to an invinately continuous flowrate of approx 11 litres/min.

formatting link
Heat Bank Combi -

Incoming water is instantly heated running through a plate heat exchanger (as is most instantaneous combi's) that takes its heat from a "domestic hot water only" store of water at approx 80C (instantaneous combi's take the heat from a heat-exchanger heater via the burner). A fast acting thermostat ensures the boiler pumps all of its heat into the store ASAP with a recovery rate about 5-8 mins from cold. The 80C water is blended down to about

45-50C. They are generally two stage flow rates, in that when the thermal store is exhausted it reverts to what the burner can produce, which is approx 11-12 litre/minute. e.g. Vokera & Worcester floor standing models (standard washing machine sizes).

N.B. The heat bank is a variation of a thermal store, but is "not" a thermal store in the conventional sense in that a coil carrying cold mains water runs though a store of hot water kept at about 80C. Heat-banks are far more efficient and give higher flowrates than conventional coiled thermal stores. The stainless steel plate heat-exchangers do not scale up so easily.

5) Combined Primary Storage Unit

(Not classed as a combi, but a derivative of a combi, but still a one box solution, so still in the same family)

These are a combination of a large thermal store, or heat bank, and boiler in one casing. The units are large (larger than standard washing machine size) and floor mounted. The heating is taken off the thermal store, which in many cases the DHW taken off the store using a plate heat-exchanger (heat-bank). Unlike the Heat-bank in 3) above the thermal store supplies heating "and" DHW, giving the "combined" to the title. They are available from 1 to 2.5 bathroom models. Gledhill do an excellent condensing version, the Gulfsream 2000.

formatting link
2), 3), 4) & 5) have high flowrates. No. 1 "generally" has low flowrates but there are always exceptions and some can be high - e.g. the ECO-Hometec infinitely continuous combi, actually has a very high flowrate. Nos 2), 3), 4) & 5) use stored water, but in different ways. Unlike No. 1 "some" versions will eventually run cold, but that takes quite a time, hence some are referred to as "two bathroom" models, having the ability to fill two baths with very fast recovery rates. As hot water is being drawn off the high rating burner is also reheating. Very rare do these combi's run out of hot water in average use. When taking one shower the burner may be re-heating faster than what can be drawn-off. No. 3) above uses stored water but will not run out of hot water (high and low flowrates). Most versions of No. 4) above are two stage flowrate models (high and low flowrates) and will also not run out of hot water.

There are combi models that give hot water and heating simultaneously as Combined Primary Storage Units do. Most don't as they are hot water priority.

Reply to
IMM

Many thanks for the info IMM, I shall study it tomorrow - can't take it all in now since I just got back from the pub! :-)

Basically what I want is a shower that nails you to the floor and a bath that fills up in 3 minutes.

M

Reply to
Markus Splenius

40kW units are available from a number of makers. Some like Man do 76kW one IIRC (you will need a pretty serious gas supply for that ;-)
Reply to
John Rumm

Then check specifications very carefully, particularly as regards issues like two flow rates. Some of them are a con.

Boilers with some form of storage are able to deliver the volume of hot water of the store initially - basically limited by mains flow rate, and then the rate will fall to whatever the boiler can provide on an instant basis, and that can be a great deal less.

A decent sized bath will take approximately 120 - 150 litres of water. You would be hard pushed filling that from many mains supplies in 3 minutes anyway. A 39kW boiler (e.g. Worcester Greenstar will give about 16 litres per minute of water at 40 degrees and winter mains temperatures, so basically you would need a boiler or other arrangement able to store a good 80 litres or so of hot water at 60 degrees or even higher to be able to mix with cold.

Remembe that it doesn't matter how sophisticated a system might appear to be, it can't exceed the basic laws of physics....

Reply to
Andy Hall

What are the limitations of a "standard" gas supply? I have a 3 bedroom detached house.

M.

Reply to
Markus Splenius

I've had fitted an alpha cb50 for exactly those reasons and it fits the bill perfectly

Shower will take your skin off, and bath fills v quickly with scaldingly hot water (you can of course turn the thermostat down)

only drawback of converting from the old HW cylinder was that the new pressurised system found lots of tiny leaks in the old radiators - so I'm gradually replacing them

John

Reply to
Jape

Then you definitely don't want a combi. To fill a bath in three minutes to an adequate temperature in winter where the incoming mains water is cold is a no no with a combi. You'll need a storage system. Which of course, some combis incorporate, but then it's not truly a combi.

Reply to
Dave Plowman (News)

Around 60kW.

Don't forget that you have to allow for other appliances like hobs and ovens in that, so practically maybe 50kW....

Reply to
Andy Hall

Hmm, did you get lots of tiny leaks in the compression joints in the pipework too? I wouldn't want to replace all my ground floor ceilings! I suppose you can fit a valve to limit the pressure in the CH circuit?

M
Reply to
Markus Splenius

-- snipped description of combi boilers ---

hometec range since they quote their flow rate at a lower temperature rise of 30K rather than the normal 35K that other manufacturers use. However the ECO 38 is likely to have a very good flow rate since it has a power of 46kW. Their efficiency figures are also weird because they use a figure of 110% to represent 100% efficiency!

Further more that are extremely expensive.

However I'm sure they are very good.

BTW: Worcester-Bosch do a 40kW Combi. Again they are quite expensive. Once you go above 30-35kW the prices rise rapidly.

W.

Reply to
W

Take no notice of this.

Reply to
IMM

62.13 kW in fact. In reality you can go about 25% over that as the U6 meters have 100% overload. But private sharks Transco will only stick to 212 cu foot/hr and charge to uprate.

Reply to
IMM

You can work out the results on the simple mass, specific heat and temperature rise.

Net figures as used elsewhere in Europe as opposed to the gross figures used in the UK. Some people have difficulty understanding the concept of latent heat unfortunately.

Just good value for money.

Mmmm.

Reply to
Andy Hall

A spec. is a spec.

Reply to
Andy Hall

They changed the specs to suit themselves.

Reply to
IMM

Then you use two combi's. The outputs can be combined for the bath taps using two check valves and a small shock arrestor after the valves. Check with the makers first. Worcester say you can using the Juniors. This is highly cost effective and you can get 50-60kW combined output using two cheapish combi's. Mid range combi's are cheap as they are the bulk of the combi market and are competitive.

Best to split the outputs of the combi's: one does one shower, one the other, etc and combine the outlets for the bath. One can also do downstairs and one upstairs giving easy and cheap zoning.

A few installers are now using this method as it solves many problems very cheaply.

Reply to
IMM

Perhaps you'd give the figures for a domestic combi that will fill a standard bath with hot water in 3 minutes in winter? And of course, one which doesn't store any water since that's no longer a true combi, but a form of storage system...

Of course you can't, because such an animal doesn't exist.

Sad you didn't make a new year resolution to tell the truth and stop peddling your usual misinformation.

Reply to
Dave Plowman (News)

I make a good living repairing combis. I have an open vented hot wate

cylinder at home and a regular boiler. You couldn't get me to put combi in to replace that if you gave it me. I would actually think yo were mad. If you offered as a means of filling a bath quickly anothe combi I would call for the men in white coats.

Thank goodness combis are so popular, I'm guaranteed work for man years to come.

Thank goodness I have enough intelligence to learn from other people mistakes and kept my airing cupboard

-- Paul Barker

Reply to
Paul Barker

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.