Dude, I don't want to sound mean, but it does not seem you know what you are talking about. Cast iron rads are not a heat source. They are part of a system that distributes heat within your home. That said, I have been heating with an OWB for many years and it is a great system, once you have one properly setup and you learn how to make it work.
If you have cast iron rads in your house you have a hydronic heating system, meaning it uses hot water to distribute heat. You did not give too much in the way of important details. Initially, I was thinking you have a newly built log home with no heating system yet. But the fact that you have those rads in place is very important and it will make life a lot easier for you! The way most people plumb an OWB (which, in this case, stands for Outdoor Wood Boiler) is they run insulated PEX tubing underground to their existing heating system, usually in the basement. Because the OWB is an open system with lots of rusty water in it, you do NOT want to plumb the system directly into your existing internal heating system network of pipes. You want to get a plate heat exchanger and pipe it inline with your existing network of piping. Get a bigger plate exchanger, as they come in all sorts of sizes (the bigger the better!).
The way it works is the water being pumped into your home from the OWB goes into one side of the heat exchanger and exits on the other end. Water from your inside furnace network of piping is hooked into the other side of the heat exchanger and it exits the other end. The water is kept from mixing by the plates in the heat exchanger. The water from the two systems flows in opposite directions.
Your best bet is to hire an expert HVAC guy or a good plumber. This is rather easy to install, but a qualified person can make sure it is put in correctly. It should not cost more than a couple of hundred dollars to do and the work is rather easy. There are lots of guides posted all over the internet on how to install these. You can get the plate heat exchangers pretty much from any OWB dealer or on ebay for a couple hundred $$.
WoodMaster makes excellent OWBs! They are one of the top quality OWB manufacturers and they have been around for a while. Best of luck to you!