Using with heart rate strap?

(1) Yes, it will pair with an ANT+ HR band.
(2) Yes, this is a nice feature in that you get the best of both worlds; higher accuracy at times you need it and the activity is one known to be troublesome for wrist-worn optical HR monitors, plus freedom from a wet/cold chest strap at times when the optical HRM works well such as steady runs.
(3) Once per second when in an Activity I believe, though if Smart Recording is enabled it may reduce the frequency of recorded data. I know it does that for GPS (check every second but not put it into the data file every second in Smart Recording), not sure if it does that for HR.
(4) Relative to the 24x7 then yes.

I have the same accuracy problems with the oHRM, and as I have the FR220 chest HRM I want to use it with the FR235. My question is are they compatible? And how can I use it instead of the oHRM?

The chest strap should work fine. You just need to pair it with the watch one time. After that, if you're wearing your strap after you select your activity, the watch defaults to the strap and automatically goes back to the OHRM after you remove it.

all i have to do is pair it? Great! . . . but how?

all i have to do is pair it? Great! . . . but how?

thanks

Here's the manual page on pairing to ANT+ sensors: http://www8.garmin.com/manuals/webhelp/forerunner235/EN-US/GUID-AE5D9A3D-4AC1-4968-829B-549DAF0ED564.html

Short version: hold it really close

Yayyyyy i am connected!

Yayyyyy i am connected!