Ventilation for old house which built in 1960's or more years ago

Older Houses with No Ducts or Fans
Intentional ventilation was a foreign concept to homeowners of houses built 60 or more years ago. Open windows could sometimes induce a breeze in hot summer periods. Open windows were also the standard ventilation for most bathrooms. Houses were so air leaky that the common goal was to reduce ventilation, rather than to promote it.

However, ventilation should be considered if these houses have been tightened as a result of renovations and energy retrofits. While opening windows will still play a part in a ventilation strategy, people are reluctant to leave them open long enough to ensure adequate air quality control. At the very least, bathroom or kitchen fans vented to the outside can be installed to control moisture in these areas. Sometimes, ducting can be retrofitted into chases or installed on the basement ceiling, if the homeowners want the benefits of an air distribution system. Do not install ducting systems in the attic, as the temperatures in Canadian attics are inappropriate for ducting in both the summer and winter. Cross-ventilation, through windows on either side of the house, can contribute to an increased ventilation rate.

Houses with Bathroom Fans and Forced-Air Furnaces
This is the basic system for older houses. The bathroom fan vents air from the house. Infiltration matches the rate at which the exhaust fan vents air outdoors, and outdoor air enters through various leaks in the house envelope. The furnace fan and ducting system can mix this fresh air with house air and distribute it around the house. In new houses in some parts of the country, the “ventilation” fan switch is located by the thermostat so that the furnace distribution fan can be turned on at the same time as the ventilation fan to ensure ventilation air is distributed and circulated evenly throughout the house.

Is this the best way to run a ventilation system? Probably not, but it can be made to work. First, install a good bathroom fan vented to the outside. Make sure that it is highly energy efficient (less than 50 watts) and quiet (1.5 sones or less), so you can use it without getting annoyed. Make it small (25 L/s or 50 cu. ft./min.), or ensure that you can control the speed. Leave it running all the time, or at least when the house is occupied. That ensures that some fresh air is entering the house. If your furnace or air conditioner is running frequently, then the fresh air is being distributed. You can leave your furnace fan on to ensure distribution, but that will usually cause high electrical consumption. New furnaces can be purchased with DC motor fans that can be controlled to run at under 100 W at low speed. Older furnace fans have power consumption of 400 – 600 W.

If you have an inefficient furnace fan and need to use the furnace fan for distribution, consider getting a fan-cycling control device. This controller can be used to turn the furnace fan on for 20 minutes per hour, for instance, to reduce the fan motor electrical consumption. Even 20 minutes an hour should ensure adequate circulation. Having the ventilation fan electrically linked to the furnace fan will ensure that when you turn your ventilation system on the furnace fan comes on too and the fresh air gets to where it is needed.