I need to install a water line for a new fridge, and would like to know what is on the other side prior to drilling a hole in the floor - is there any tool which would let me place a "marker" or a "beacon" where I intend to drill the hole, then go into my basement, and find where it would end up on the other side if I were to drill there?

edit: I have done my best to measure/map it, unfortunately I don't think it's very accurate since I don't have a good point of reference on both levels. I was hoping for something other than drilling a pilot hole, because there is an air vent that runs in that general area, and I don't want to poke a hole in it

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    Is the outlet for the fridge behind it? Wiring going up from the basement is always a great reference point.
    – Comintern
    Aug 7 '14 at 23:08
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    @Comintern there is an outlet, but the wires lead into the ceiling above the fridge, not down into the basement. Aug 8 '14 at 1:12

The most common technique (other than careful measuring and mapping) is to drill a very small pilot hole through the flooring alongside the baseboard. The hole can be less than 1/8 and you can run a straightened clothes hanger through the hole to find it in the basement.

The hole would probably be behind or under the appliance, if the location were good, or it could be filled with wood putty or something similar if it shows.


A couple really strong magnets might work. Place one on the floor where you want to drill, slide the other along the underside of the floor until you feel them meet.

The top magnet might slide along the floor to meet the bottom magnet, in which case you'd have to reposition the upper magnet to exactly where you want it before marking the spot. The bottom magnet should stay mated though, so it should move along with the upper magnet.

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    Would there be any way of telling if there are any nails/etc. that would skew the results? (I don't have strong enough magnets.. but this does seem like something I should try) Aug 7 '14 at 17:20
  • I guess metallic objects inside the floor might be a problem.
    – Tester101
    Aug 7 '14 at 17:30
  • FYI Every concrete ceiling has metal. Else it would just break down.
    – kaiser
    Aug 11 '14 at 11:56

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