A.Don Fugler, a senior researcher with the Canada Mortgage and Housing Corp. in Ottawa, Ontario, responds: If you leave a house deserted in winter, the biggest risks are to finishes and furniture due to cold temperatures and extreme humidity (high or low). The safest, most convenient way to minimize problems is to provide a modicum of heating. Keep it to about 50°F (10°C). If you build an energy-efficient house with good solar gains, the heating costs for the unoccupied winter periods will be low, and you will avoid the inconvenience of draining plumbing and removing all water-based stored foods and supplies. A small amount of continuous ventilation is also useful for keeping the air fresh. (I agree that a hydronic heating system might be risky in this situation.)

If your customers are intent on leaving the house unheated, there are some precautions I would recommend. Ventilation is particularly important. Running an efficient set of fans (a ducted HRV, for example ) continuously at low speed will mix air and keep the house fresh. Also, you do not want solar gain in an unheated house, because temperature...

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