Venting subfloor up the chimney?

I'm thinking 2 birds one stone here.....
I've been told I need better underfloor ventilation (there's no ventilation at the back of the house, just the front).
We are doing some refurbishments so it's as good a time as any to rip the floor up and put a couple of snorkel vents in the back wall.
And i'm blocking up a fireplace and apparently supposed to vent the chimney. As it goes against the grain to send hard earned warm air up the chimney I thought of venting the space under the floor into the unused chimney instead.
It seems like a no brainer to me.
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On 21/07/2019 13:17, R D S wrote:

And to me.
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On 21/07/2019 13:17, R D S wrote:

only possible downside is that it increases sub floor heat loss which may be an issue if the floor is poorly insulated
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It’s easier to fool people than to convince them that they have been fooled.
Mark Twain
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On 21/07/2019 19:21, The Natural Philosopher wrote:

We're in the process of covering it with 25mm polystyrene 'boards' and T&G Caberfloor, so should be OK.
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On 22/07/2019 11:30, R D S wrote:

Make that 65mm and its still nowere near enough...
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On 22/07/2019 11:30, R D S wrote:

30% heat loss through the floor. If any air leaks between those inadequate insulation panels then you might as well not bother.
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On 22/07/2019 16:33, Andrew wrote:

There's nothing there now. Except the floorboards.
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On Sunday, 21 July 2019 13:17:24 UTC+1, R D S wrote:

Just do it in a way that is practical to undo. A flat we blocked the chimney in became stuffy & damp, reopening the chimney solved it.
NT
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