Suggestions on where to go for sizing a home system

We live in Central Ontario, and we are looking to slowly move off grid. This fall we would like to install solar tubes for radiant heat, and oversize it for domestic hot water. We built our home about 5 years ago, we have ICF basement and R40 walls on our main level. We heat primarily off wood heat, but have a small hydronic air handler as backup(right now we have a boiler system hooked in, but if solar tubes can produce enough heat it would be nice to tie into this as backup as well). Our basement is plumbed for radiant heat, as well as tiled areas on our main floor. The problem I am having is figuring out realistic BTU production for Ontario, how I should figure out or requirements based on our existing system. Is there any online resources that people use to help size systems?