First, thank all of you answer my questions and teach me plumbing/heating abc.
We are going to discard the solar panel hot water system. Our plan is remove it from roof and hang it on a wall to heat my house during the winter by heating air flow (a plan only).
We will convert to gas as soon as possible.
Now is the hot water system.
It looks like we have three options:
1. tankless; after read this article, http://www.foodforthought.net/learn-...-tankless.html, i am afraid of the climate affect.
2. indirect gas fired hot water tank;
3. gas fired hot water tank.
I asked similar question in HVAC section but did not get few responses. As a professional and home owner, what's your choice? which one is better between 2 and 3?