Most chimneys, especially in urban areas are redundant. The trouble is that they still perform one of their primary functions whether they have a fire in them of not – effectively taking warm internal air and putting it outside. At the same time cold air is drawn in due to the low pressure caused by the rising warm air.
End result – higher energy bills and thermal discomfort from draughts.In the diagram on the left the blue arrows in the loft space indicate a properly ventilated loft which is needed to keep the rafters and joists dry and prevent rot. The ventilation comes from the eves.
The traditional solution to redundant chimneys is to slow the air movement down by semi blocking off the fireplace openings but installing vents to allow a trickle of air to enter. The chimney pots usually have a horizontal cover put on them to stop rain entering but still allow air out.
The reason for now blocking off the chimneys totally is so that any moisture that does get into the chimney can get back out. This happens either by penetrating the brickwork from outside or moist air penetrating from inside and water condensing as it cools.The problem with this solution is that warm air is still lost, just as a slow rate.
We’ve got 6 chimneys in two stacks. One of which, on the ground floor north side of the house will be retained as a working chimney with a small wood burner. The wood burner is small enough to not require additional ventilation to be installed.
The other five need some attention. The plan is to totally cap off the chimneys and the fireplace openings but to ventilate the chimneys – essentially sealing the chimneys off from the inside of the house but allowing outside air to trickle through them and into the loft space. The ventilation will help keep the underfloor timbers and loft timbers dry.
The chimneys will be connected by short lengths of pipe, with the bottom fireplace connected to the underfloor void with a small length of pipe.