Window air conditioner with extension cord safe?

[Tricia O'Brien]

Is is a big safety hazard to plug a 5000 BTU air conditioner into a heavy duty 6 ft or 12 ft extension cord and then plug that extension cord into the wall?  I know the manufacturers do not recommend this, but I was wondering if anyone has done this and did it work out well for you?

 I have an Indiana rental home where the central air conditioner just  quit working and I have decided to give the tenants some window A/C units instead of replacing the old one due to cost.  They prefer 3 small units (one for each bedroom) rather than a large unit in the living room and one in the kitchen. I just discovered one of the bedrooms does not have an electric outlet next to the window.  So I'm trying to figure out a solution, and I think it would take at least 2-4 weeks to find an electrician to do a small job like adding one electric outlet to this room.  Plus might be several hundred dollars. Thanks for any input! 

[Nathan Gesner]

Quote from @Tricia O'Brien:

Look at the air conditioner label or user manual. It will tell you how many AMPS the A/C unit uses. Then go to the hardware store and ask for an extension cord rated for the number of amps required, or better. These tend to be shorter (10 feet or less) and heavy duty (12 - 14 gauge wire).