How do I fix an irregular hole in my heater closet?

The plumbers cut a roughly rectangular hole in the water heater/heater closet floor when fixing the drain pipe for the condensate line. The closet is located in the garage. There are two 2" PVC pipes coming out of the middle of the hole. Can I patch this without removing the water heater and air conditioner and replacing the entire plywood floor? What's the best way to do this?

Here's the "before" pics; I've included two images from two slightly different angles to help with the perspective:

Here are the "after" pics:

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Can you add a (link to a) picture. The size and shape of the hole might dictate the solution. – ChrisF Nov 13 '10 at 15:53
I think Niall C. gave me what I need...but I'll definitely get a before and after pic uploaded for anyone else who has this same problem. Thanks! – Shane Nov 20 '10 at 2:40

You'll need to square up the hole and do some careful measuring and cutting, but it can be done:

1. On the floor, mark a rectangle that encloses the existing hole. Ideally, the two pipes would be parallel to an edge, but it's not essential.
2. Measure the distance from the two closest corners to each of the pipes.
3. On some plywood, mark a rectangle the same size as the rectangle you marked on the floor.
4. Add 1/2 the outside diameter of the pipe to the distances you measured in step 2. Using a drawing compass, mark an arc with the appropriate radius from each of the corners. Where two arcs intersect will be the center of the pipe.
5. Using the drawing compass, mark a circle the outside diameter of the pipe.
6. Mark a line across the width of the rectangle going through the center of the two pipes.
7. Start cutting: cut out the rectangle on the floor, cut out replacement rectangle, cut along the line through the center of the pipes (this needs to be a thin saw blade), then cut out the four semicircles.
8. Cut out the rectangle on the floor.
9. If you've got room under the floor, you can use some wood under there as strapping to help hold the replacement pieces in place. If not, you'll just have to do the best you can with wood glue.
10. Put the two pieces around the pipes; they should be able to slide up and down. Again, if there's room under the floor, use a piece of wood as strapping to hold them together; if not, glue and hope for the best.
11. Slide them down into the hole in the floor. They should fit snugly into place. Screw them into the strapping if you were able to install some, otherwise just glue them in place.
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