I’m not 100% sure how to model every detail, but hope to point you in the right direction. Open energy pro 8 and from the menu select the help dropdown and select contents. Then type “Hydronic”. Click on the “Hydronic Systems” topic.
It sounds like you are modeling a “combined hydronic space and water heating system”, so I’d recommend reading that section and following their directions as best you can.
I have found that referring to the 2019 Residential Compliance Manual sections that they reference is also helpful. It looks like they reference sections 4.7.1 and 4.7.2 which also may have helpful info worth checking out. That document is free and can be downloaded from the CEC’s website here:
I believe the water heater will have to be approved in the CEC’s appliance database. You will need to search the database and find the water heater you plan to use. There are two ways to search the database at the paths below. Note that regarding the filters, less is more when searching the database. I often use only 1 filter then export the data to excel and search from excel, rather than clicking through the result pages on the website.
See attached image for the epro help menu.