[Strawbale] Distributed ventilation

[dfugler at cmhc-schl.gc.ca]

Good morning list,

Rob is right (as usual). If you do not circulate fresh air, some rooms 
will be underventilated and some overventilated. Running the furnace fan 
to circulate ventilation air is the way that cheap builders do it. It is 
low first cost (no new ducting) but a high operating cost, so most people 
do not use this system (see http://www.cmhc-schl.gc.ca/odpub/pdf/63615.pdf 
). Furnace fan energy consumption can be lowered either by cycling the 
furnace using a product such as AirCycler or by installing a furnace with 
an ECM or equivalent motor, which uses very little electricity at low 
speed. Most straw bale houses though don't seem to have furnaces anyhow, 
so this may be moot. A ducted HRV, with supply air to the bedrooms and 
exhaust from kitchen and bathrooms, is the most efficient way to 
distribute fresh air in the house. The full ducting, instead of using the 
furnace ducting, can cost you another $500-$1000 at the time of 
construction. If you do it yourself, it will cost you much less (and you 
will probably do a better job). Make sure that you do diligent HRV 
maintenance (see http://www.cmhc-schl.gc.ca/odpub/pdf/64994.pdf)

Trickle ventilators do not work in two story houses in cold climates, 
because they act as exhausts in the bedrooms upstairs even if they are 
installed as intakes. Trickle ventilators and a continous bathroom fan 
might work in one storey houses in moderate climates, but their actual 
effectiveness depends upon building airtightness (which leads us back to 
the blower door thread ...), and how well the room in question connects 
aerodynamically to the room where the exhaust fan is located. Tight inside 
walls, a closed bedroom door, and a thick carpet might make the exhaust 
fan in another room completely useless for providing fresh air to yours.

Don Fugler
CMHC Policy and Research