I was scanning Webasto section on the Heatso site and run into this thermostat which can control blower speed proportionally to temperature delta. Will work with Kalori blowers but it could work with Rixen blower. This could be a good information for hydronic heating system to make them quieter.
https://www.heatso.com/webasto-blower-control-unit-thermostat-kit-for-rv-camper-blower-boxes/
https://www.heatso.com/search.php?search_query=kalori blowers§ion=product
https://www.heatso.com/webasto-blower-control-unit-thermostat-kit-for-rv-camper-blower-boxes/
https://www.heatso.com/search.php?search_query=kalori blowers§ion=product
