My wife and I live on an acreage just outside of Edmonton, Alberta, Canada. Our house faces south and has a walkout basement. The foundation is ICF and the 2-storey house is a timber frame with 7″ thick EPS  SIPs surrounding the frame. The roof is 10″ thick SIPs. 
The house is heated by a 1990 Lars Teledyne non-condensing boiler using in-floor heating on the main and second levels, the basement slab and the attached garage.
Domestic hot water is heated by the boiler’s hot loop and the 5 heating zones for the house via its’ cold loop.
We are installing a 15kW ground mount solar array and want to replace our gas-fired heat source with an electric one.
Our radiant floor system has not been needed since May and that huge boiler is just heating the domestic hot water. Additionally, when we built the timber frame and attached it to the garage, we were living in, the inspector made us have a backup heat source. So to satisfy the inspector we installed a high-velocity fan with a hydronic heating coil in line with the HRV. We also took advantage of this and added an AC coil.
So I am trying to remove the 1990 gas-fired boiler and replace it with a properly sized electric way to heat domestic hot water and the radiant floor zones in the winter. So I am trying to size it appropriately for our house and to determine amperage requirements. I would really appreciate any enlightenment into determining the correct size.
Thanks