I may have made a mistake. I just bought a tankless hot water heater with 1/2 inch water connection fittings. My house used 3/4 inch water pipes. Is it OK to reduce from 3/4 to 1/2 inch copper pipe and connect to the hot water heater and then as the water leaves the heater to go back from 1/2 to 3/4 inch copper pipe? Thanks for any info!