Central heating upgrade

[Roger]

The message from [e-mail] contains these words:

You are sounding more and more like Dribble every day. The difference in efficiency is only marginal. The larger thermal capacity may even be an advantage in a boiler that doesn't modulate. You even played the typical Dribble trick of inserting an additional qualification to bolster a weak argument. Take out the "a given physical boiler size" and you can match the surface area.

What could make a significant difference but which you fail to mention is the difference in thermal conductivity between Aluminium and cast iron but there again that is more a question of size constraints than any inherent unsuitability of cast iron.

Now why would the op be disappointed to find that the boiler in question has say a 70% efficiency rather than the 50ish% that you said was his lot.

[DavidM]

Had mine replaced about 9 months ago. 35 (+) year old Potterton cast iron boiler supplying 9 rads and indirect cylinder to give you an idea of the size. Had the new boiler, a Worcester Bosch Greenstar 24i, installed in a new location about 8ft above where the old one was, so some pipework changes needed. New flue out of the roof, new pump, programmer, valves, and condensate pump. System power flushed the filled with inhibitor. Total cost £3.6K, took 3.5 days (about 6-7 man days). Really struggled to find someone to do it, they seem to cherry pick the easy jobs. HTH David

[Kostas Kavoussanakis]

Indeed. My 25-yy Potterton Netaheat is 68% efficient, says sedbuk. Thanks for the link Roger!

I personally wish it lasts another 50 years, if at all possible, though I would love to move my boiler to the attic (not recommended; flue availability and it may well break in the process). Mr Friendly Local Gasman gave it its annual service last month and said it's in really good nick. That's the way (a-ha a-ha).

Kostas

[meow2222]

It isnt, much of the heat stored in the exchanger is wasted at each switch off.

in the real world boilers are of limited size

less significant that the fin design

comparing an old cast iron job to a modern boiler is liable to lead to decision to replace it. That is the disappointment.

NT

[Roger]

The message

from [e-mail] contains these words:

So you say but like Dribble you don't stop to think where the heat actually goes and what effect it has on the in house environment. And I would take issue with you on the amount of heat involved when the thermostat stops calling for heat . Would you care to produce some real figures to back up your claim?

But by no means all the same size.

If you think that then there really is no hope for you.

Not to anyone who can add 2 and 2 together and get 4 rather than the square root of minus one. In most cases the economics of having a boiler in good working order replaced are dubious at best and not to be contemplated if the replacement cost has to be borrowed.

[Dave Plowman (News)]

Not if you fit a pump over run so that energy it transferred to either the heating or hot water.

[Doctor Drivel]

This man is a barking mad plantpot. Do not take any notice of him.

[Doctor Drivel]

Only when new and working well designed and efficient system. It is more like 55%.

[Doctor Drivel]

This amateur is barking mad and should be ignored.

[Doctor Drivel]

Total tripe!

Correct!

[Doctor Drivel]

Very true!

[dennis]

Mine has over run, however as it is fully zoned it can't dump the heat into any of the zones. I made it dump it into the airing cupboard via the bypass pipe.

[Dave Plowman (News)]

It will dump most of its excess heat into the room it's in anyway - which may or may not be a good thing. Mine is in the bathroom which can rarely be too warm. If it's situated outside the house it could well be just wasted. I do wonder about these quoted efficiencies. I recently changed from an ancient cast iron type to a state of the art condenser - and although there have been worthwhile savings the gas usage isn't in direct proportion to the quoted efficiency increase - although I'll need a bit longer to get a better average. I'd guess they're a bit like official car MPG figures - a lab. measurement which can't take real world usage into account.

[Roger]

The message from "Dave Plowman (News)" contains these words:

Can you monitor your return temperature?

Condensing can give you up to an extra 10% but you won't get any of that if the return is above 54C and you may never get the return low enough to give you the full measure as that temperature is well below most peoples comfort zone.

[Roger]

The message from "Doctor Drivel" contains:

Absolutely nothing of any consequence.

As usual Dribble has nothing positive to add to the discussion so he resorts to his very limited range of insults.

Meanwhile something for the Dribbles of this world to get their teeth into:

"Condensing boiler technology is evolving rapidly. A fully condensing boiler with a cast-iron heat exchanger has been introduced in the United States. It deals with the corrosive nature of the condensate produced in it by increasing the wall thickness of the heat exchanger sufficient to deliver an expected residential life of four to six decades and by discouraging the conditions that accelerate corrosion."

If Dribble and his pal are to be believed that would be a condensing boiler with an efficiency in the region of 65% at best. :-)

[meow2222]

incorrect again. The heat goes partly into the water in the exchanger, which is not flowing, and partly up the flue to outdoors. The heat that has gone into the water then has many minutes in which to cool off and give its heat to the outdoors. So its almost all lost.

Effect on in house environment is insignificant. Exchanger heat is not lost to indoors.

How much heat is stored in the iron depends on the boiler design. The point remains valid regardless of how large it is.

and?

no valid point then

in many cases, but clearly not in all cases. Replacing an iron boiler running at 55% with a new one at 80-90% makes a big saving, justifying quite a lot of boiler cost.

Lets take an example. Say an 85% boiler costs =A3600 a year in gas, so a

55% one would cost 600x .85/.55 =3D =A3927 pa, thus there is a =A3327 pa fuel saving from replacement. If a new boiler costs =A31500, that's a 21.8% pa return. Over a 20 year life it would save =A36,500 on fuel. We could subtract an arbitrary =A3500 in extra maintenance costs and the =A31500 buy & install cost to give a =A34,500 benefit. But not worth it you think.

NT

[meow2222]

No-one has made such a claim. We were discussing old iron exchanger boilers decades old. You and facts eh.

NT

[meow2222]

=BF=BD2000000?

or get a landlords safety certificate for =C2=A350.

yup

NT

[The Natural Philosopher]

No? come and stand in my boiler room sometime :-)

I agree a lot goes up the chimney..one reason for a proper flue INSIDE the house to get the last drop out rather than a balanced flue - but a fair amount leaks out of the boilier casing itself.

This heat almost certainly WIONT go up the flue..

>

[Dave Plowman (News)]

The boiler spends pretty well all its time in condensing mode judging by the plume from the exhaust.