Thank you for your response. Let me add additional information for you.
When we built the house the addition was already included in the heat estimate although we did add and additional heated 150sf to total 3500 sf. In addition to the appollo heating system (main floor) we have a heat pump for the second story where the master bath is added. We also have a main floor gas fireplace. These are both used as secondary heating sources. As a clarification on the appollo system. The hot water cycle's from the hot water tank through the heat exchanger and then back to the hot water tank.
I live in NC where the winters are not that severe.
Will I have problems keeping the hot water tank full ?