Off topic, but I can somewhat answer that. Just had the final installation work done on air-air multi-split heating/cooling for our average sized 4-bed. Two outdoor units, feeding seven indoor wall-mounted units.
In heat mode, one outdoor unit is rated at max 1.4 kW AC power input and the other at 1.7 kW. So a hair over 3 kW total if working flat out. House is reasonably well insulated, so I doubt we'll see those figures very often.
Next on the list is disposing of the gas boiler and rads.