Which boiler system for efficiency?

[Dave Plowman (News)]

Your real choice is between combi, combi with some storage, and pure storage. Which hot water system would suit you best depends on many factors.

[Cameron]

Hi

Trying to decide on a new boiler system!

The question - Assuming all the boilers are of a similar efficiency, i there an efficiency advantage of a using either a combi boiler, or a open vented boiler or a system boiler?

Although an existing system Im not bothered about the work load! or t some extent the additional fitting requires

Camero

-- Cameron

[Ed Sirett]

For this question we have a FAQ - see boiler choice below.

[Christian McArdle]

An directly comparable instantaneously combi will be more thermodynamically efficient in the provision of hot water than a storage system. Whether it will meet the household needs is another matter.

A sealed system might be more efficient than an open vented one, as open vented ones frequently go wrong in a way that reduces energy efficiency.

Christian.

[Dave Plowman (News)]

Really? Think if you did a straw poll on here of previous posts you'd find far more about faulty pressurised systems.

[Ed Sirett]

On balance I think sealed systems are to be preferred. They have one major weakness which is the expansion vessel which is compounded by many user's refusal/ignorance to attend to this problem when it arises , and some professionals tendency to fix symptoms (power flush) rather than the cause (replace the expansion vessel).

When an open vented system is wrongly installed then the problems are far far worse, a significant proportion of systems are incorrect. Once the air is out and they are working they there are a number of fairly minor problems, (sticking float valve, limescale plug at entry to circuit) which are fixable.

I really can't be bothered to see if there are many more posts or not about sealed systems versus open vented, I hadn't noticed, you may be right.

BTW sealed primary does not imply combi. My own house has a sealed primary but pump assisted vented DHW.

[Dave Plowman (News)]

Ok.

The answer to that is to install it correctly. It's hardly rocket science.

Possibly, but will take many years. I'm still waiting for my first fault like that.

Of course it may be just that there are more pressurised systems. But then that might be offset by the fact they're also newer.

Absolutely.

[Christian McArdle]

These days, I would think that a significant majority of installations are of the sealed, pressurised type.

Also, we are talking about energy efficiency. Faults in a sealed system largely result in failure to work at all.

Many typical faults in an open vented system result in the system working inefficiently, due to such nasties as pumping over, leaving a header tank full of hot water.

Christian.

[Dave Plowman (News)]

I'd agree, but being newer why so many problems?

That's not so much a fault as poor design.

[Christian McArdle]

Not surprising, as it is easy to perform a poor vented design and the people who design them are largely muppets. With a sealed pressurised system, the design is so simple that it actually gets done properly.

Christian.

[Doctor Drivel]

A one pipe combined feed and vent is virtually trouble free. Install a Magnaclean on and an air ejector and they work well indeed.