Willis immersion heater suitability

[Vic]

Hi all, read with interest, the thread on Willis immersion heaters. Which made me think they may be a solution for my home. 

It's a small Victorian box. Three rooms downstairs (which is all below ground level. Except for about 60 or 70 cm) with a flat roof. 2 Bedrooms and bathroom will be below the open plan living space upstairs. Roof is flat.

No damp proof course. The basement floor will be coming up soon a layer of glass beads/volcanic rock (I'll need to check and edit that) laid to allow the moisture to escape from the walls. DPM and then a concrete slab with underfloor heating. Bedrooms will have log burners and bathroom a large electric rad. Could the underfloor be heated with the Willis immersion heaters? The slab will be approximately 4m x10.

Outside the walls will be insulated, paths repaired to lessen any additional water getting into the walls. 

Wood fibre insulation has been installed. An electric boiler (think it's an Actec) heaters the water in a small sealed cylinder. At some stage solar will be added to the roof with a battery store.

Think that about covers it. Sorry if its a bit vague, just currently scratching my head and pencilling in plans.