How many turns should I be able to turn by hand before needing a wrench?
The reason I ask is I have a heating box from Navian that has 1in and 3/4in NPT stubs on the bottom.
When trying to thread a connector it goes about 1 to 1 1/4 turns before needing a wrench.

Put it this way. You should have about 3.5 to 6 engaged threads and you;ll need to tighten about 2-3 turns past finger tight.

Yes, it does require some effort. Since they are tapered, there is variablility in how far the pipe was threaded.

Don't forget to use teflon tape or pipe dope. Pipe dope recommended for gas lines.

The stub that is coming out of the bottom of the heating box is not tapered. It is a brass stub. I will be using female copper connection to change to copper to go to the manifold.
Also the female part coming off the manifold I will be using a copper connection.
That is what I don't understand, the NPT thread is for pipe that has a tapered thread. What about when you want to change it to copper, the copper connector is not tapered hence you don't get the 3.5 turns or so.

I have put a link below to show what it is.

DK1010 Deluxe Manifold Assembly Package, Stainless Steel Manifold Accessories, Radiant Heating - Watts Canada (http://www.wattscanada.ca/pages/_products_details.asp?catId=1165&parCat=2071&pid=4510&ref=2)

Post a direct pic on this forum using "go advanced/manage attachments".

It may be compression.