DIYbanter - View Single Post - Combi boiler - condensing

wrote:
Sponix wrote:
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.

Cars often have a temperature controlled flap that diverts the
incoming air via the radiator in order to warm it up.

Cold air is denser so you get more air per unit volume to support
combustion so they also fit intercoolers to cool the air before it
enters the engine.

Yeah but cars are internal combustion engines, not CH boilers so I'm not
sure the argument's the same. Intercooling in a car maximises the power
output which isn't the desired object of pre-warming the air in a CH boiler.

Tim

MBQ