combi vs conventional

[Colin eclipse 2]

I know - done to death.. A customer has asked me this question. I have come up with the following list. Any other thoughts - sensible ones.. no need to start a debate about the merits - just need a list!

Conventional Pros Stored hot water - so water (hot and cold) available if mains supply fails Immersion heater backup - hot water if boiler or gas fails Warm airing cupboard Cons Cylinder needs replacement (in this case to comply with building regs) Storing hot water not as energy efficient More complex controls More costly than combi to install

Combi Pros High pressure showers without pumps Only heats hot water you use No stored water (flooding issue) Frees cupboard space Cons slower bath filling No warm airing cupboard

[tarquinlinbin]

Conventional wins hands down for me,especially in higher demand situations.. It seems to me that storing hot water isnt really a big issue becuase of the turnover rate, i.e not stored for a great length of time. Well insulated storage vessels and lagging plus possible use of plastic piping would lower heat losses even more. Compare this to lower flow rates and wastage of water run off and for a family home,its conventional all the time,preferably pressurised stored system.

Just my views for what they are worth.

[Set Square]

I'm not at all sure that a system based on a conventional boiler *does* have more complex controls. More complex external controls, perhaps - but the diverter valve in a combi is at least as complex as (say) a mid-position

3-port valve - and seems to be at least as unreliable based on posts in this NG.

Also on the Cons side for combis, you only get a decent flow of hot water if you've got sufficient heating power in the boiler *and* a mains cold water system with sufficient flow capacity. Many houses don't have sufficient cold flow capacity, and *need* to have stored water systems.

[Cicero]

==================== You can have the best of both worlds if you have the space. Conventional boiler for CH only and a separate 'Multipoint' for hot water only.

Cic.

[geoff]

In message , Colin eclipse 2 writes

Combi pcbs are more complex and tend to be a bit more expensive than conventional boilers

Conventional boilers (correct me if I'm wrong) tend to have an immersion heater in the HW tank giving DHW backup

[Andrew Gabriel]

That's what I've got. It wasn't really by design -- multipoint blew up a month before I was going to put heating in (see the FAQ humor section for the details;-) Buying a new one had the hot water back working in a few hours. Having got a brand new one, it didn't make sense to rip it out when heating went in, so boiler just does the heating, and multipoint does hot water.

[IMM]

-This is so rare an event that is it is not worth taking into consideration.

That can be achieved with any heating system, so not so.

-Cylinders may need replacing every 8 to 10 years in hard water areas.

-Very poor shower pressure, having to use an expensive and noisy power shower pump in some situations.

-The cylinder takes up space.

-Ugly zone valves and pumps around cylinder.

-No wating for cylinder to reheat

-HIgh pressure shower after shower can be taken.

-Have a high output, so house warms up faster.

-All the system is inside the one white box.

-No pipes to freeze in the loft

High flowrate combi's are available, so not true.

A small rad can be installed in the airing cupboard taking up no space.

[IMM]

Not so. A few combi;s don't have 3-ways valves in them.

[Lurch]

On Fri, 18 Jun 2004 01:18:47 +0100, "IMM" strung together this:

Well, he didn't actually, I snipped it all. I was going to point out the glaring errors, but got bored of typing.

[Andy Hall]

It happens to me every few months......

One can use a water softener or phosphate doser to avoid this. If the water is untreated, then heat exchangers on some combis are liable to scaling.

Flow from a combi can also be poor if it is not a large one.

So does a combi if of high capacity and fitted with some form of storage.

One can have a system boiler.....

This is irrelevant if the cylinder is adequately sized.

That depends on the water supply and temperature and rating of the combi.

Than what? A system boiler can be equally effective.

A system boiler can achieve that as well, with the exception of the cylinder.

Irrelevant if they are properly insulated.

We've had that debate and there are demonstrable limitations.

A post suggesting that there are no disadvantages to combis should be regarded as suspect. Nothing is ever as clear cut.

.andy

To email, substitute .nospam with .gl

[wattie]

consideration.

Where do you buy these 'zero volume' radiators? I could do with a few of them!

[IMM]

Mr Poll! Bean, now refrain.

[IMM]

consideration.

Stop making things up.

Water softener at approx £400 just to buy then the cost of salt too and they take up space. A de-scaler will only delay the inevitable.

You size accordingly. Many conventional boilers will not fully heat a house and leave the occupants cold in winter. So, when you fit one you size to suit. You don't undersize. The same with combi's.

Such strange logic. A conventional system takes up two lost of space and a cylinder takes up lots of space unless you go square like an Elson. You obviously can't figure this out.

You still need a 3-way vale or TWO 2-way valves.

You mean oversized, taking up space and more standing heat losses.

You size to suit. Duh...

Combi boiler by their nature have outputs. Conventional boilers are sized only for a particular house requirements. A combi in 90% of cases will have spare heating capacity.

...and the cylinder takes up lots of space and has standing heat losses and a 3-way va;lve has to be installed as well.

Which is more expense.

Stop babbling balls..."High flowrate combi's are available".

You know nothing of combi's to come out with a ridiculous statement.

[IMM]

The ultimate zero volume rads are forced air or underfloor heating. Go for it.

[Dave Plowman]

Sounds to me like the worst of both worlds.

[Christian McArdle]

2 port valves are usually much more reliable than 3 port mid position valves, though.

Christian.

[Christian McArdle]

As the cylinder needs replacing, you'll also need to explain the relative benefits of different storage systems.

1. Unvented cylinders.
2. Heatbanks
3. Conventional gravity fed.

Christian.

[Dave Plowman]

Really? Happens here in London often enough to be a consideration.

Perhaps you advocate instant electric water heaters above every basin etc just in case?

Do you source them from China, like your power tools? Good quality ones won't be effected by hard water - why should they?

As opposed to poor flow from a combi fed one?

Some might say them being easily acessible a benefit. Of course they would be ugly if you fitted them since you're not a plumber...

Never heard of fast recovery cylinders?

Becuase they will allow the above...

I take it you always fit undersized conventional boilers if you have problems with speed of warmup?

So it all needs replacing at once with some failures?

You've not heard of insulation? Strange.

Please give comparitive costs of uprating incoming water and gas mains, and the extra cost and size of your little white box that can do all this to match even a modest storage system in this respect?

Did you get frightened by a storage system as a child, or is installing a storage system properly just beyond you - the most likely explanation.

[Andy R]

And they don't restrict the flow so much.

Rgds

Andy R

[IMM]

Correct. A heat bank may the perfect solution to their requirements and functionality, space and cost.