Definitely slower speed for a coil type exchanger for hot air, But with a baseboard system if you have a flat plate exchanger I found that faster moving water is the way to go. I originally had a taco #9 on the plate exchanger loop and wound up going to a #11 on the OWB(130ft run),and a grunfos 3speed on med on the inside circut to heat the inside boiler. I noticed an immediate difference how the temp on the inside system was not pulled down as fast when there is a call for heat.