Several things come into play with these generators. The size generator that you have chosen will only deliver 120 volts at 1600 watts which is little power.
This type generator can also be used with a companion generator but that companion generator must be a designated generator and not just any old generator will work. Not even two of the same make and model will work together it must be a companion generator.
When two are connected together you will still only have 120 volts. There is no way to achieve 240 volts using two at one time. To jumper from one leg to the other leg in order to make both sides of the panel hot is a very bad idea and even dangerous.
Under full load this little box will go through a tank of fuel in about 2 ½ (from experience) hours and when two are being used the fuel use doubles. Not much savings when two small generators are being used in the place of one larger one.
In order to be installed in a code compliant manner they must be connected to the premises wiring through a transfer switch that switches the neutral or they must be connect to the premises wiring as a Separately Derived System.
These types of generators are designed to be used with cords. In order to save money and I think that is the purpose of using one of these, plugging a cord into the receptacle of the generator and into the load being used is the proper method of use.
If it is your intention to use one of these for heat you might want to rethink your design and spring for something of value like a 30kw type generator. Unless you heat with gas or oil this little bugger will not be of much help and if you do have gas or oil it will be all that little box can do to start the fan motor to running if it will start it at all. It will take about 4000 watts to start a ½ HP 120 volt motor which is more than two of these units will pull.
Then we come to the best part, the warranty. Unless this generator is installed and used according to its listing and labeling then the warranty is void. For more information to the listing of this generator see UL White Book FTCN. The information about the warranty voidance can be found in the equipment manual.