We've been making  a lot of effort insulating and sealing up our house in order to save money on our bills and reduce our CO2 emissions....so there is no point punching lots of holes in it in the bathrooms and kitchen....equally we don't want a damp and (smelly) house. One option would be to install a whole-house mechanical ventilation with heat recovery (MVHR) system and another is to install individual room heat recovery units in the key areas.

Both work on similar principals - exchanging heat from moist smelly internal air to the fresh outside air as the first is expelled and the second is introduced into the house. They do this by passing them through heat exchangers.

The system I am going for constantly monitors the humidity of the internal air.  The humidity level can be set for difference rooms.  when the humidty is below the setting the fan runs at its trickle speed of 19m3 per hour and when it is above it runs at 38m2 per hour.

The trickle uses 9Watts (and 21dBAs noise level) and the boost 46Watts (and 45dBAs). They can also be installed in damp bedrooms as they come with a light sensor to stop them going onto boost mode at night.

It's claims are a heat recovery up to 86%.

Essentially the extract unit looks very similar to a normal extractor fan but there is a bit more technical stuff inside - filters and heat exchangers.

We are going to be putting in four.  One in each of the main bathrooms and ensuites and one in the kitchen.

The only other component is the isolating transformer unit that also has the humidity sensor and boost override cord.  This is positioned away from the unit so it can get a more accurate reading of the humidity in the room - useful when the SELV fan is installed in a shower enclosure.


The whole units cost a bit more than a normal extractor fan but a mixture of the savings and importantly having a comfortable damp free house will make it a worthwhile investment.

Running costs
I've estimated that the running costs of the four fans will be around £48 a year if we didn't have a PV system.  With the contribution from the PV system and the fact that the boost Wattage will not be on at night I estimate it will cost us around £27 a year in electricity.

In terms of heat energy, they will of course lead to greater heat losses than a totally sealed bathroom/kitchen but the realistic would be a 0% heat recovery normal extractor fan which would lose a lot more heat. I'll calculate the heat savings over a normal extractor fan in a follow up posting when I install them.

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.