Help with removing a swarm from a chimney flue

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It got a bit cold tonight so we turned on the heater and several bees started to appear.  I think they are in the gas flue and any advice on how to remove them would be very helpful.  I think the may have only been there for a few days - tomorrow I'll try to confirm where they are chimney or flue.  I hope they haven't made too much wax yet - I don't want my house to burn down.  Just hope they're not my bees that have swarmed.
Can I spray insecticide down the flue?  I would prefer to save them but This is going to be a difficult scenario.  The wife is not fond of bees in the lounge room.

Thanks for your suggestions