These photos show the way the previous owners of my house used a jack post to brace sagging floor joists. I'm not sure of their method, so I wanted to check what the correct method is.
Typically, there is a beam put under the joists, then the post are put under each end of the beam. This detail is better suited for longer beams, covering more joists. Somebody has found new and unusual ways do do something there. I can see the logic of what they were trying to do, but makes for a lot of guessing still.
The problem really happened when the insulated pipe was drilled through the bottom edge of the joists.
I would strip everything out of there, completely, after adding temporary wooden posts under the two joists. This includes the steel post, all wood blocking and extra joists, metal strapping, etc., right down to the bare original joists.
I'd then place a doubled joist crossways between the two joists in play, screwing it in place through the original joists. I'd then add double heavy-duty joist hangers, upside-down, on the end of the cross-joist, tying it to the original joists and transferring their loads.
I'd then mount the post to the bottom of the doubled cross-joist using 5/16" x 2 lag screws.
_____________________ |x| |x| |x|\ cross-joist /|x| <--- screws/lags through original joists |x| | (doubled) | |x| |x| | | |x| |x|_|_________________|_|x| -------- hanger --↑ || ↑ -- hanger || | | | | < -- post | |
Tl;DR The "correct method" is to remove that pipe and sister in replacement joists. The job that the previous owner did is a hack job / bodge job, and I wouldn't trust it.
A jack post is used to reduce the span of a beam. The problem here isn't that your span is too short, it's that the capacity of your beam has been destroyed by drilling a large hole near the bottom of it. The solution isn't to use a jack post but to repair the beam.
The "best" way to do this would be to restore the beam to its original size by sistering in a replacement joist, but this of course can only be done if you remove the pipe that the hole was made for in the first place.
If you want to keep that pipe, you'll have to investigate other options. Potentially connecting a replacement beam underneath the joist would work, if clearance isn't an issue. You could even put a jack post underneath that additional beam if you want.
The above all applies to each joist that needs strengthening. They way the owner has tried to use a single jack post for two joists looks unsafe to me.