Running your furnace fan 24 hours a day. Unless you have an HRV, do not do this in the winter.
Older furnaces have blower motors that use a lot of electricity. Modern furnaces use fans with brushless motors which draw so little electrical current that they can be run 24 hours a day.
I once lived in a house built in 2001 by MacLachlan & Mitchell Homes. A Production Builder specializing in entry level single and multi-family homes, they were conservative about adopting new building techniques. At the time, they claimed to be the only builder left still dropping the main floor joists into the concrete walls when they were still wet.
Our house had rounded corners, which saved me minor injuries on a number of occasions. The standard square corner cap can be quite sharp if you accidentally run into it with some force behind, and a friend tells me how his mother went into the hospital the last time before she died after running into one when confused.