We are in the process of remodeling our bathroom and will be adding a shower to our tub. The tub has a roman tub faucet with 2 handles. I understand I need a diverter to run the water to the showerhead. We will just be using the tub faucet and a showerhead, so would I need a 3 or 4 port diverter? Thanks in advance for your help.
To do this right, you might need to tear more up than you think. A tub doesn't need the federally mandated anti-scald valve. Once you add a shower, you do. If your existing valve does not have that, technically, you should replace it with one that does when you add a showerhead. The easiest way to handle this would be to replace the tub spout with one that has a divertor built in and replumb the supply after the valves with a twin-el so water can go either to the spout or to the shower head.
Another big factor might be that a tub without a shower may not have been built to handle the spray resulting from a shower. You might rot out all of the walls and deck. One way around this would be a circular (or oblong) surround shower curtain, then no spray should hit the walls.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013