We are looking to add onto the house. Our present furnace ~60K Btu is inside the house of ~1200sf
We are looking to add ~800sf to our house.
a) How do I decide what is the best size for our new furnace or whether we can use the present one. (our present furnace is about 1 yr old). The contractors that came in just did a rule of thumb and said I need ~90K Btu. I have read you can do a J calculation to find the correct size but noone is willing to do that. Does it take a long time to do so?
b) Some of the contractors say you can put a 90K in the same space as we have but others say I will have to go the attic. I am afraid to put it in the attic because if something breaks what do I do? Also how do I replace filter? But then I don't know how I'll fit in the same space.
c) As an added bonus question, we do have a 3tonne A/C. We hardly use the A/C but everyone was saying I have to go to 4tonne A/C since I am upgrading the furnace so the condensor coil needs to be upgraded as well.
Sorry for the long email but I'm a newbie