1in NFT threads

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.

That doesn't sound right. I would expect minimum 2½ to 3 turns by hand. Are you sure you are not mixing straight threads and pipe threads? Or some kind of mechanical thread instead of pipe thread?

threads

There is no "standard". It depends on the quality of the tap and die that made the respective threads. If they are both "new" the threads will go further. If they are both worn, you might have your situation. And if they have different degrees of wear, the thread will be somewhere in the middle. What really matters is HOW tight you make them AFTER that point, and that is also a subjective matter, which depends on the size of your wrench and your physical power.

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 witch is nickle plated shutoff valve, I will be using a male 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.

http://www.wattscanada.ca/pages/_products_details.asp?catId=1165&parCat=2071&pid=4510&ref=2

A standard copper female or male NPT adapter is indeed tapered. You may have some kind of straigt thread fitting which needs a gasket. How about some pics