Farside
Badly Welded Man
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- 6,178
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- Ireland
The boiler flue is plenty large enough and has a decent draught.I would think itis less than a kW (extractable), so unlikely to get much from a secondary heat exchanger. Better to extend the hot exhaust so the heat is lost directly to the warmed area. Look up the heater specifications (not the marketing carp) and compare it to the energy content of the fuel.
Any exhaust (or the other pipes) must be increased in size (cross sectional area) to avoid constricting the fan operation. Failure to do so will likely produce more CO, more sooting-up and wastage of fuel.
But hey, thanks for the unwanted lecture. I'm beginning to suspect you read a lot of manufacturers' brochures, like some other ones we've had on here.