[miamicuse]

I guess I am not following fully, you said the other side is the garage, which I assume is not heated but you will run the PEX exposed? This wall is not insulated either, are you planning to insulate the PEX tubing?

 

[750mV]

I guess I am not following fully, you said the other side is the garage, which I assume is not heated but you will run the PEX exposed? This wall is not insulated either, are you planning to insulate the PEX tubing?

The wall is insulated to some extent, I removed it for the photo.
I've asked a few people about insulation, I'm not clear myself. Most of them said don't bother with insulation around the tubing. These were from estimates I got from plumbers, but they were going to install the PEX outside the wall.
This is for the hydronic heating system.

 

[HotRodx10]

This is for the hydronic heating system.

Then I don't understand the hesitation to run it along the wall in the garage. It'll be flowing warm/hot water during the heating season. Certainly when it's cold enough for the temp to be below freezing in the garage, the heating system will be operating, right?

 

[HotRodx10]

I was hoping to use 1.5x3" plates. This is the reference I found:
Digital Codes

P2603.2.1 Protection against physical damage.
In concealed locations, where piping, other than cast-iron or galvanized steel, is installed through holes or notches in studs, joists, rafters or similar members less than 1¼ inches (31.8 mm) from the nearest edge of the member, the pipe shall be protected by steel shield plates. Such shield plates shall have a thickness of not less than 0.0575 inch (1.463 mm) (No. 16 Gage). Such plates shall cover the area of the pipe where the member is notched or bored, and shall extend not less than 2 inches (51 mm) above sole plates and below top plates.

I'm not sure what you're reading that indicates a 3" plate would be sufficient. I understand the text you posted to indicate you'd have to extend the plates even farther than I thought - 2" above and below the pipe, so a 5" long plate.

 

[750mV]

Then I don't understand the hesitation to run it along the wall in the garage....

I'm just taking the recommendations of the plumbers who looked at the job. They did not want to use the garage.

 

[750mV]

... - 2" above and below the pipe, so a 5" long plate.

I think the 2" refers to the sole and top plates, not to the pipe being covered. There are probably others here that understand it better than I do.

 

[HotRodx10]

I think the 2" refers to the sole and top plates, not to the pipe being covered.

It probably refers to the length along the sole plate or top plate for pipes passing through those plates (vertically). The width of the nail plates is pretty much always 1 1/2", the thickness of a 2x, so it covers all of the edge.