I plan on buying a Raypack pool heater 014940 (P-R336A-EN-X). it requires a 1 1/4in gas pipe. My current pipe is 3/4. 

Can we convert from a  3/4 to a 1 1/4in pipe in order to make the fitting work ? and if yes, will it affect the operation of the heater ? i am thinking you have a certain amount of gas in a 3/4 line and if that gas goes at some point into a 1 1/4 in pipe, the pressure will decrease. not sure if this has an effect on the heater. 

Thanks for any help.