Combi fans: is bigger better

[IMM]

He did a lousy job for you.

High flow combi's can be wall mounted.

[John Rumm]

Yes _some_ do, the great majority do not, something you often fail to point out I notice.

Perhaps you could compile a list of those you know of which are able to provide DHW and CH simultaneously?

(I suggest this not because I doubt they exist, but because the information might actualy be useful to someone in the future)

Huh? Write English please.

[John Rumm]

Hmmm lets see....

So when someone says "I am going to catch a plane to Scotland". you say "why not drive?" they say "It takes too long" you say "High performance cars are available"

Nope the analogy seems spot on to me. The recommendation is correct and yet fails to take account of the practicalities of the situation.

That could be your tag line.

So, many peoples *experience* is of poor (or poorer) flow from combis, and yet because you and I know that it does not have to be that way, then all of a sudden their actual experience must be imagined? Did they step into the IMM perception distortion vortex then?

So what? most people have never taken or been offered your advice.

The latter is certainly true. I know when I have spoken to people who are in the process of getting a new combi boiler, they will often make the assumption that the size of the house (and hence the CH requirement) dictates the size of the boiler, rather than the HW requirement. Perhaps it comes from applying the same logic to selecting a combi that would have been used for a system boiler. Often they have not even thought about the flow rates they will get, and their so called heating "engineer" has not explained it either (probably not wishing to jeopardise an easy sale, and a quick no hassle install).

You mean "Do as I say, not what I do"?

[Pete C]

Hi,

Is 160l up to the overflow, before anyone gets in? ;)

Also I would have thought mixing 60°C water with a third cold would be enough whatever the cold temp, the limit on thermostatic showers is typically set to 42°C.

cheers, Pete.

[Andy Hall]

Nope - although it depends on Archimedes of course.

That would be making the assumption that the water reaches 60 degrees.

Combis are quoted with a flow rate based on a temperature rise of 35 or sometimes 30 degrees. Therefore, the quoted rate will only be achieved when the water going in is at 25 degrees or more. This is way over-optimistic and only achieved in long periods of hot weather.

In the winter, water temperature averages 5-8 degrees so at the stated flow rate, water coming out will be at shower temperature.

The relationships are all linear.......

.andy

To email, substitute .nospam with .gl

[IMM]

Why? are you going to run out and buy one before the shops close?

[IMM]

Stop being silly.

< snip silliness>

That is sad. they should read here and take it.

That is sad. They should read my posts here.

No, I mean "I suggest you don't comment on topics you obviously know nothing about".

[John Rumm]

No, I was just giving you the chance to contribute something of value to the group. I know, you think it is too much fun arguing about anything and nothing in particular to be bothered to do that.

The sad thing is there is a good proportion of the stuff you post that could be useful. If you could balance some of the advice you offer with some real world pragmatism, i.e. give the cons as well as the pros then newcomers to the group could make a balanced decisions based on the relevant information.

Instead you insist on posting answers based on "black and white" thinking all backed up with messianic "trust me, I can tango, the rest of you are plebs" style rhetoric.

Avoid too many "night is day", and "the laws of physics don't apply to me" arguments, and the rest of us won't have to wast time highlighting the pitfalls of your suggestions. You may even find the rest of what you say might have credibility.

[IMM]

My advise is full of pragmatism, it just happens to be over your head.

< snip as I am not into third world reasoning >

[Dave Plowman (News)]

But the adverts and websites he quotes from are unlikely to give the down sides.

[MBQ]

How many bad ones have you experienced?

MBQ

[Pete C]

I see, maybe that's where the IMM concept of 2 boilers comes in, there is an extra one hidden in the attic to boost the DHW :)

I reckon most people could wait an extra 5 mins for the bath to fill, I'd be tempted to get in when the bath is half full.

Also for a larger 40kW combi 16l/min at 35°C should be enough for a decent shower.

cheers, Pete.

[IMM]

message

What is meant by bad?

[Bob Mannix]

message

I didn't say I had. On the basis that larger = more hot water and better flow, the very large ones I have seen were OK in terms of flow but not brilliant - I wouldn't want to have less flow than I experienced from them. If you are going to tell me that smaller combis (ie something the size of my current CH boiler on the wall) would provide greater a flow/temperature combination than a 1m^3 floor mounted jobby, then I am happy to reserve judgement until I have used such a beast (perhaps you could give details). You will note that I had two reasons for not using one. The second reason was flow.

[IMM]

litres/minute, and goes on the wall.

Not a problem if you get the right model. It is like saying all commercial vehicles are crap because a Mini van does hold much. If you need to carry a lot of stuff you get the right vehicle. The same with combi's

[Bob Mannix]

Yes you quoted that before and I have no reason to argue/disbelieve the figure. If this is a larger flow rate than these very big combis I have seen on the floor, why do people buy the big ones that go on the floor? It's not my floor, so I'm not bothered either way, but just interested.

[David]

This is indeeed a good boiler, and it is on my shortlist, if I go down this route, BUT it is worth noting that the quoted 22l/min is for a 30C temp rise, for a 35C rise then you are down to just less than 19l/min. I had thought that there was some vain effort to standardise on a 35 C temp rise, every time I see a figure >20l/min it turns out that they either have a small built in storage capacity or quote for a 30C rise.

cheers

David

[Andy Hall]

This is a MAN Micromat

have one of their system condensing boilers and it is excellent.

If you want a larger model, there are others in the range distributed by MHS Boilers.

.andy

To email, substitute .nospam with .gl

[IMM]

flow/temperature

This boiler is svery expensive. Well it is in the RR class, that is why.

[Dave Plowman (News)]

Yes. A Mini van after all costs the same as an artic.

Does money never enter your little planet?