I have to replace my 85,000 BTU oil furnace. All the sizing calculators recommend 45,000 to 50,000 Btu for my size home and location. I can get a 55,000 BTU unit but the 84,000 BTU unit has a better heat exchanger warranty and better burner and is air cond. ready. What problems could I run into by oversizing the furnace? Thsi is the second furnace replacement in 25 years both due to cracked heat exchangers. Could the oversized furnace cause this?