Your proposal will involve at lot of mess, a lot of hard work and I am not sure what you will gain?
Before you start, think of under floor heating more in terms of back ground heating.
If you use UFH as your main source of heat, then you will find it hard to control.
These large concrete blocks take ages to heat up!
More importantly they are slow to respond to rises in temperature.
You may end up having to open your windows to let the heat out, when the sun shines.
This being heat you will have to pay for!
Think of light weight UFH, which will respond much more quickly.
I undertook a similiar project for a customer except we put in electric cable, not a pipe. the reason we did like that is that the customer didnt want to raise the floor. It was extremly dusy and very hard work, it took two day for two people but we did it and was able to put the carpet back over once the quick drying screed had gone off, customer was extremly chuffed and he said it works very well.
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