Alt-H was conflicting with the Help menu on Windows.

Let's try Alt-2....
diff --git a/Lib/idlelib/config-extensions.def b/Lib/idlelib/config-extensions.def
index 28f917d..c02f431 100644
--- a/Lib/idlelib/config-extensions.def
+++ b/Lib/idlelib/config-extensions.def
@@ -26,7 +26,7 @@
 [ZoomHeight]
 enable=1
 [ZoomHeight_cfgBindings]
-zoom-height=<Alt-Key-h>
+zoom-height=<Alt-Key-2>
 
 [ScriptBinding]
 enable=1