Moderator Post (s) for this thread: >Locating Cablesbythiggy on 02/11/2009
There are several methods.
NONE GUARANTEED.
A non contact electrical proximity detector. Also know as Tick Testers. These run about $10-25 and HD and Lowes has them. Then are pen shaped devices. For your purpose the ones with adjustable sensitivity is better.
The heat as to be on at the time that you run the test. And if there is metal lathe behind the plaster it might not work.
As with all of the test don't just find a small spot. But map out a large area and verify that what you have found is an evenly spaced pattern.
But from other threads on ceiling heat that the wires might be on 6" centers and don't really leave much room for anything else.
The other methods are to look for the heat. For this it is best to have the head off for couple of hours so that the ceiling is cool.
Then turn on the heat.
The cheapest is to mist the ceiling with water and watch the patern as it dries. Don't know how well it will show on the ceiling. This method is used on concrete floors.
Use infra red. Non contact infra red thermometers are fairly inexpensive. But most of them have too wide of view so that you need to be a few inches from the ceiling.
A thermograph. This is an infra red picture of the ceiling. This is used to find insualtion and energy problems in homes. People that do energy rating have them. The HVAC contractor should know people that do this.
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