"Andy Hall" wrote in message
...
On Sat, 1 Oct 2005 23:22:17 +0100, "RedOnRed" wrote:

Older boilers fired up on maximum burner rate. They controlled the water
temperature by switching on and off. A modulating boiler can reducing
the
flame size. So assuming the output and heat exchanger are the same,
there
will be no difference in heat up time.

So what's the point of the modulating large and small flame?

Isn't it to control the rate of heat?

My old boiler wouldn't modulate and would heat on fixed flame which would
be
lesser then a full on modulating one in my new boiler, which would surely
heat faster on full modulation?

A bigger flame means quicker heat doesn't it? Or is my sense of logic not
modulating right?


The only reason that a newer boiler, be it condensing or not would
heat faster than an older generation one would be that the newer one
would typically have a stainless steel or aluminium heat exchanger and
the older one perhaps cast iron.

The point about modulating is three-fold:

- The boiler can run continuously rather than on/off for more of the
time. Cycling, especially with a cast iron model is less efficient,
especially with an old conventional or non-fan-assisted model where
excess heat at the end of the cycle ends up outside.

- A modulating boiler can begin to turn down the heat close to the
desired temperature for the house and reduce temperature overshoot.

- On a condensing boiler, operating at a lower temperature results in
more efficient operation.


No-one seems to have picked up on the rating of a replacement boiler. If the
old boiler was 60,000BTU/hr and ther new one is also 60,000BTU/hr then it
will modulate "down" from there and never up past it. Thus the rate of heat
up at maximum will only be the same as before. (Give or take a little bit
for a cleanbrand new heat exchanger)