In article , John
wrote:

"Nige" wrote in message
...
In article ws.net,
Doctor Drivel wrote:

"Nige" wrote in message
...
With the recent massive increases in heating oil prices, I've been
wondering if there would be anything to gain from replacing my existing
Grant Multi Pass oil-fired boiler - now around eight years old - with a
newer model.


Go to:
http://www.sedbuk.com Go to oil boilers then refined search. Pick your
boiler and see what the efficiency is. It probably have drop a few
percent.
Then look at the efficiency of the condensing boilers.

Work it out from there.

Many thanks for the tip.

From what I can gather, my current boiler is rated at a 'C', offering
around 85% efficiency - whereas current models are rated at 'A' which
equates to an efficiency of around 95%.

The makers defined efficiency when new might be relevant but in view of your
remarks about the service guy replacing baffles but not giving you any
combustion analysis or report figures I'd not be sure the boiler is
operating anywhere near that efficiency now. Efficient use of fuels does
depend on checking the combustion at periodic service. How can you or he
have any confidence in the effectiveness of the combustion otherwise?
I strongly suggest you insist on him carrying out combustion analysis tests
when servicing and on seeing his combustion readings from these tests. If he
is doing the job properly he WILL be carrying the correct test equipment.
Most commonly a chemical (Fyrite or Briggon) test set as these are more
tolerant of oil flue gases than oxygen cells in electronic analysers.

For what its worth a surface coating of soot on the inside of a combustion
chamber is an excellent insulation barrier to heat transfer into the water,
A displaced or missing baffle allows the heat to escape the boiler before
absorption into the water, too rich a fuel/air mixture produces soot (smoke)
and poor combustion efficiency, too weak a mixture burns all the fuel but
the excess air sweeps heat straight through the boiler and out of the flue
so again poor efficiency. The efficiency curve has quite a sharp peak.


Would this 10% increase in efficiency offer me a straight 10% saving in
running costs - or is it (as I suspect), more complex than that? And
where does size (output) of the boiler enter the equation?

It will give you a cost saving BUT you need to do a proper costing exercise
before spending lots of cash on replacing your boiler, especially if you
intend to fund it with borrowing. Bear in mind that the present price of
heating oil is not likely to stay at its present level. The price of crude
fell lately and this will slowly filter through to the end user. Heating
fuel prices do vary widely between different suppliers over the year from
winter to summer. Normal practice is to have a tank big enough to hold a
years supply and buy when its cheap.

The output rating of the boiler "should" have been designed to match closely
the needs of your installation, but oil boilers of domestic sizes are
generally not built to modulate. They switch on/off under the control of the
boiler thermostat. When the unit is fully loaded in deep winter its
performance will be at maximum efficiency. As the season warms up the duty
cycle of the boiler will become more off than on and the true efficiency
will be much lower, eventually in summer the only load will be hot water.
Under these circumstances switching on from cold will show a steady demand
to heat the cylinder but once it is heated only small burst of replenishment
heat (subject to the cylinder thermostat) will be required. Under these
conditions you will obviously not get the same efficiency as during winter
with full load demand.

The Grant multipass is a decent boiler so unless there is a deterioration
problem I would not expect the sums to justify replacement purely on the
gain in efficiency for a reasonable payback. however do make the effort and
work it out properly for yourself.

Many thanks for this detailed reply - you raise some inteteresting
points.

Unfortunately, any cost/efficiency analysis I could carry out would
inevitably be compromised by the rather er... 'unusual' house in which
I live - a thatched former dairy, listed (to prevent the replacement of
the ill-fitting steel window frames), laid out in a long L-shaped row
of rooms, with wind (I kid you not) gusting through the loft areas
because is isn't the practice in this area to put felt (or any other
kind of membrane) between the roof timbers and the thatch.

Needless to say, insulation has been a number one priority, but as long
as the planners/listed building officers here in Dorset continue to
value authenticity more highly than saving the planet (or my wallet),
I'm stuck with what I've got. And I won't even mention the construction
of the walls...

But ultimately, I think you've answered my questions. It probably
wouldn't be worth changing a functioning boiler for a more efficienct
model - but that I really need to keep on top of servicing and make
sure the engineer caries out combustion tests.

Other than that, I suppose it's down to waiting for Bush to vacate the
Whitehouse and hoping that peace might break out in the Middle East.
Shiiishh...

Thanks again...

Nigel