Tankless hot water to heat home
Just get a combi if you need both DHW and heating or just an 'only heating' boiler. Few brands names: Immergas, Baxi, Buderus, Bosch, Riello, Junkers.

If you get I condensing unit I suggest you to keep the flow below 55°C, to exploit the condensing capability of the unit.

DHW units usually aren't suitable for space heating because those units lack a feedback control on water temperature (they assume inlet is standard 'acquaduct' range: 5°-20°, so returning with hot water may cause serious issues bringing water to boil in the exchanger leading to steam production and eventual explosion)