I'm trying to install an ASHP system into a large detached house built in 1950s.

After completing the insulation, the heat load of the house was calculated and the system specification is a dual heat pump system comprising of a Diaking Altherma LT 16kw and 8kw heat pump. 16kw for downstairs and 8kw for upstairs. We're planning to use fanned radiators to allow flow temperature of 35-40 degrees.

All that is just fine, but my installer submitted a request to the DNO and they've come back saying that we need split phase supply installed as the total load will be over 100 Amps. The house currently has a single phase 100A supply.

I understand that of inrush current for compressors is often high but these systems are inverter controlled and have soft start to limit the inrush. I don't think the DNO are considering this.

Does this sound reasonable? Has anyone else had this problem?