Hi all,
I am new here, so bare with me
We have bought a new house with 22 yo furnace 100,000 BTU in Ontario, Canada.
The house is rented as 2 floors (main+basement) to 2 families.
The house is probably build in 70s

We had few contractors coming over to give us the quote and get a different story all the time.
Most recommented 60BTU furnaces, where one did some extensive calculations and recommended 40BTU. The main floor is 1000 sq feet, the basement is probably 600-700. The price is same between 40BTu and 60BTU. I am concerned taht we are significantly undersizing the furnce if we go with 40,000BTu's. And since I have tenants there it makes it even worse if they start complaining that it is too cold.
I think the house has very-very basic insulation in it.
What do you guys think?