Unused chimney breast - ventilation required?

Hi,

We've had the chimney stack removed on our 1930's bungalow, and it's been left open at loft-level. There's no loft conversion, and it's a cold loft with insulation between and over the joists. Walls are cavity construction without any insulation.

If the stack were still in-place, I'm aware that we'd need to have a ventilated cap on the chimney pot and a vent at ground level in the lounge fireplace/breast (to provide ventilation and avoid damp).

However, with the stack removed, could we get away without ventilating at ground level to minimise heat loss? ...or are we asking for damp problems?

Thanks in advance,

Terry