Additional Heat Exchanger / Economiser on Boiler Flue?

2 Mar 2010
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United Kingdom
Has anyone had any experience with a heat exhanger (or so called "Economiser") which goes between an OFCH boiler and the flue stack?

I've seen a home made system which was clamped onto the top of the boiler exhaust, with the original flue then slotted into it, comprising a stainless steel tube within another stainless steel tube (roughly 20mm gap between them), with additional pipework (roughly 25mm dia) running across the inner diameter of the smaller tube. The ends of the large tube were welded shut, to allow water to flow into the outer jacket and across the central tubing (which sits in the exhaust stream).

The feed line for the boiler line ran through this first, with the aim of pre-heating the water, and increasing overall efficiency.

Anyone seen something like this? Does it improve efficiency in the real world?
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Done some testing using thermocouples and seems to improve overall efficiency on the existing system. If anyone wants a set of drawings / CAD model for the unit, send me a PM.
alpha make one, but i have no knowledge about whether it actually works or not, its not cheap either

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