What would be the best way to add a heat exchanger to a 13hp engine?

What would be the best way to add a heat exchanger to a 13hp engine?
That would depend on what you are trying to accomplish.Add engine cooling to an air cooled engine? Try an oil cooler.Trying to capture heat to heat something like a room? A exhaust to air heat exchanger. Basically a pipe run through the room you are trying to heat.Trying to warm water off a air cooled engine. Its pretty easy, you need a coil of copper tubing, or steel. Where the exhaust comes out of the engine you coil you tubing around a pipe from there, at the end of the pipe you cap the pipe but leave a gap so the gasses can escape and slide a pipe over the whole thing so the gasses go to the end of the pipe then turn around and flow over your coiled heat exchanger. The you run water through it at the rate that gives the temperature water you want.