I looked at an EU200i today. The exhaust port ID is about 0.7" into the
muffler, which attaches with a standard looking flange with two metric
bolts. The pipe out of the muffler is about half that diameter.

It burns 1.08 gallons of gasoline with a fuel value of 123.1K Btu in 4 hours
at the 1600 W rated load, so it makes 6.4 kWh (21.8K Btu) of electricity and
101.3K Btu of heat (another 29.7 kWh), ie 36.1 kWh total, if it replaces
electric resistance heating. So cogen makes economic sense at a gasoline
price of $2/gallon if electricity costs more than 100x$2/36.1 = 5.5 cents/kWh,
in simple terms.

The ground isn't bonded to the neutral, with 60 volts from each pin to
neutral, so a grounded plug into a wall socket would damage the inverter,
so it needs to float or use an external isolation transformer.

Nick