Due to the age of my furnace and various repairs in past, I plan to buy a new 75,000 btu furnace to replace the oversized one I have now. I have a split system but my a/c is still okay. Having zeroed in on a particular brand and model, I see on internet that there are two 75,000 btu furnaces in same model and one (rated for 3 to 5 ton a/c) has 10 Mfd’s and the other rated for 1.5 to 3 tons has only 7.5 Mfd’s. Since my a/c is a 2.5 ton I prefer the smaller version. However when I see that a (same model) 60,000 btu also rated for 1.5 to 3 tons has the higher Mfd of 10, I am concerned that I could be getting a lower quality with the 7.5 Mfd. I'd certainly appreciate opinions on reasons for the lesser Mfd's and any possible problems anyone has had with a 7.5 Mfd blower on a 75,000 btu furnace.