"Andy Hall" wrote in message
...
On Fri, 17 Mar 2006 08:19:35 -0000, "Tim Downie"
wrote:

Ian Stirling wrote:

And financially!

Are there any add-on units that take the exhaust down from ~80C to
~20C, and use it to warm air to come into the house?

I've often wondered why manufacturers don't fit a much longer insulated
co-axial flue. This would reclaim much more of the heat lost in the
exhaust
by using the counter-current priciple to warm the incoming air to the
boiler. Warmer incoming air would surely reduce the work the boiler has
to
do to heat the water?

Sounds too simple so there must be something wrong with the idea although
I
can't see it.


There are several issues:

- People may not *want* to have a
long flue even though the boiler may
be able to support it.

A long plastic mPVC flue can have a pipe around it. A pipe in pipe
arrangement. This is legal as the inside of flue is not touched at all.
It could run for 10 to 15 foot across a loft and have water in the gap
between the pipes. Feed cold mains water through this and it pre-heats the
water. Zenex, pre-heat water this way with their top boxes and claim 50%
greater flow rate through a combi. So, a 12 litres/min combi can be zipped
up to 18 litres/min. Big jump.

Using a pipe in pipe means it is cheaper than their top box. But they are
incorporating it all inside one combi box. They are talking to the big
boiler manufacturers to licence their technology. If a 12 l/min combi gives
18 litre/min for the same kW input then this combi will sell like hot cakes.
Also, the plume is eradicated.

Councils are now having to deal with complaints of nuisance pluming. This
appear to be the answer.