Why does it say "ha'Mizbe'ach ha'Nechoshes"?
Radak (14, 17): Even though it is Samuch, it has the prefix Hei ha'Yedi'ah (to identify). We find like this - "ha'Mamlachos Kena'an" (Yirmeyah 25:26) and verse 17 "ha'Misgeros ha'Mechonos."
Which copper Mizbe'ach was this?
Rashi: It cannot be Moshe's - that was hidden! It cannot be the stone Mizbe'ach that Shlomo made, and it was called Mizbe'ach ha'Nechoshes, for one cannot move it from place to place without destroying it! We learned that the fire on Shlomo's Mizbe'ach did not depart from the Mizbe'ach until Menasheh removed it (Zevachim 61b). He destroyed it (Sanhedrin 103b)! Rather, "Mizbe'ach" is one of the copper lavers or Mechonos, which are needs of the Mizbe'ach, and were near the Kadosh Mizbe'ach. We find (Shabbos 55a) "va'Ya'amdu Etzel Mizbach ha'Nechoshes" (Yechezkel 9:2) - was the copper Mizbe'ach in the Beis ha'Mikdash?! Rather, [the angels] started [killing] where they sing Shirah [with copper instruments] in front of Me. We find that copper Kelim are called Mizbe'ach!
Radak: It was the Mizbe'ach that Shlomo made, like I explained in Melachim I, 8:21. (It was of copper, like it says in Divrei ha'Yamim II, 7:7.)
Malbim: I explained in Melachim I, 8:64 (it is the stone Mizbe'ach that Shlomo made in place of Moshe's copper Mizbe'ach).
Where did Achaz put the Mizbe'ach that he made?
Rashi: He removed the laver and moved it to another side of the Bayis, lest it interrupt between his Mizbe'ach and Beis Hashem. He put it by the Mizbe'ach Kadosh, to the north.
Radak: It was closer to the Bayis (Heichal) than the copper Mizbe'ach that was already in the Azarah. It was between the [Kodesh] Mizbe'ach and Beis Hashem; it was on the north side [of the Kodesh Mizbe'ach].
Malbim: He could not move Shlomo's Mizbe'ach, for it was attached to the ground. He put the new Mizbe'ach to the north of it, but closer [to the Heichal] than Shlomo's Mizbe'ach. It was between Shlomo's Mizbe'ach and the Heichal. "Va'Yakrev" refers to Achaz' Mizbe'ach; the start of our verse is connected to the previous verse (Achaz poured the blood on his Mizbe'ach, and also on Mizbe'ach ha'Nechoshes).
