Passivation

After the three years of living in a house that was cold and damp in the winter, we were convinced that a ventilation system with heat recovery was necessary to provide fresh air in the winter with minimal heat loss.  Every winter we were faced with condensation build up on the windows and the need for ongoing dehumidification. This is something we wanted to avoid in our own house whilst still keeping energy efficiency in mind, so we started to look into a ventilation system with heat recovery.  Then this winter we started to question the need for this type of system after living in a different house that has been warm and dry all winter, and unlike the previous house has required neither heating or dehumidifying.  The secret to this new house?:

1. Passive solar gain through the northern windows -  the house has most glazing on the north elevation, none on the east and some small windows on the south.
2. Reasonable insulation levels.
3. Smaller building envelope area to volume ratio - being an end terraced house rather than a standalone building like our old house and having three floors with a garage at ground floor that acts as a buffer layer rather than single level where all floor is close to the ground.
4. Has more thermal mass with concrete used in the lower part of the house and for the party wall.
5. The urban heat island effect - the house is surrounded by buildings with lots of thermal mass which help to keep the ambient air temperature from dropping too much.
6. Protected from wind by surrounding buildings so the heat loss through surface convection is less.

The house is so warm that cracking a window on a cold day isn't too big a deal (in fact we are a little worried that this house will be too warm in the summer).

We realised that a ventilation system would be solving a problem with another problem (additional capital and operational cost as well as maintenance and cleaning requirements).  We would only really use this system on very cold days of the year, so it would probably sit dormant for the rest of the year slowly collecting dust in its ductwork. Instead we are making sure that there are windows in each room that can be left open slightly during the day without leaking if it rains.  It may mean that we have to think a little more about how we use the house and open the windows, but its a much more simplistic and in my opinion holistic approach to the problem.

The high ceilings in the bedrooms will create stack ventilation in these spaces which we are hoping to utilise through some passive roof ventilation system which has yet to be selected.  This system will help remove unwanted heat in the summer and in the winter will be shut-off to prevent loss of essential heat.  At ground floor we will have small opening windows that can be left open when we are out, which will be located on opposite side of the living space to provide good cross-ventilation.