Extending flow under floor to create under floor heating

[motorbiking]

I have to move the radiator flow and return pipes in the bathroom to accommodate the refit. The previous occupant put a large double rad in the bathroom and two heated towel radiators. I'm always concerned about "correcting" over sized rads as, often you find they did it for a reason. I was wondering if anyone could see a down side to running a loop of flow pipe under the floor boards to create a warm floor effect.

I've done this by accident before and it worked well. Would it be incredibly inefficient to have un-lagged pipes like this?

 

[oldbuffer]

1. If you have air bricks venting the space between bathroom floor and ceiling below, then you will lose a lot of the heat to outside.
2. If you have no vents to outside, and the exterior wall(s) is / are insulated, then most of the heat lost from the pipes will contribute to heating of the bathroom.
3. The best approach is to do a heat loss calculation for the space, and size the radiator accordingly, remembering that you can always turn it down, but you can't turn it up beyond the limit of its heats output.
4. If doing a heat loss calculation, I'd ignore the towel radiators as their heating contribution will be very small, particularly when covered by towels.

 

[motorbiking]

Thanks - It only needs 6-700w Radiator based on the calc.