Anyone ever notice how the houses on a street all look pretty similar? Or that the amount of windows as a percentage of wall space is very similar (it is actually regulated by code in my area). Also that the insulation in structures built around the same time is pretty consistent? Another strange thing is that the ASRAE weather conditions have not changed (those are the standard weather conditions that are used to determine heat loss and gain of structures). After you do a few hundred load calls you can do them without the simple form with astonishing accuracy. Even so let’s put that aside and say that the world will end if you do not do a load calc on paper, even if you don’t have to to size the furnace. How many sizes of furnace are there? Depending on the manufacturer, there can be a 40ish, a 60ish, an 80ish, 100ish, and the mighty 120ish. Industry standard is to select the next largest size that meets the load. If so that puts you at some where from 0 - 20k oversized on heat before the safety factor built into the load calc or the oversize built into the calc for pick up (if your furnace was sized for the actual heat loss of the building and you turned it down at night it would never warm back up at or near design conditions because it would not be able to overcome the loss it was sized for). The manual J load calc is just a rule of thumb based on a few simple measurements used to select the closest unit. It is not some magical eightball. If you have been satisfied with the heat from the furnace you have had for years running a load calc will not make you any less or more satisfied with you new furnace of the same or similar size. Saying that the act of doing some simple math will make you more comfortable with NO other changes is a marketing ploy.

On the variable speed and multi stage issue, it has been my observation that it does not increase the comfort or satisfaction of my customers enough (at all in most cases) to warrant the extra expense or complexity so I don’t recommend it. Again, marketing an unneeded up sell.

ECM motors. ECM motors are just fancy variable speed motors that use less juice than a standard motor. They use a fraction less power, but cost exponentially more and fail at a higher rate. Again I would rather have a less efficient more dependable motor, but hey marketing.

It is a furnace, not some magical transformative appliance. Yes if you live in a cold climate you need one, but I am not going to take dinner guests down to look at the thing. As long as it gets the job done no need spending more money on it than required. A fancy furnace does not add a lick to resale over a basic one of the same brand.

As for my qualifications to comment on the subject if someone really wanted to figure that out it would be pretty easy, but honestly I don’t care if anyone believes what I spent my time posting or not. In fact I strongly recommend that they seek a local professional to handle their HVAC needs and put little if any stock in what they read on on the internet.

Anybody ever notice when passing by an auto manufacture or dealership how most of the cars look the same?
But when you drive by a used car lot, not so much?
Everybody doesn't live in a tract housing community or a subdivision full of alike condos. Houses can and will be built differently. A load calculation not only provides valuable information, but helps protect the HVAC contractor should legal issues arise. So in reality, its benefical to both parties.

Recommending Carrier and Trane, talk about marketing ploys. Two of the most marketed brands out there.

You didn't answer... why is it that a simple Carrier logo makes it superior to its exact same sister furnace brands (Bryant, Arcoaire, Comfortmaker, Heil, etc to name a few)?
And since "its just a furnace", why pay more for that Carrier, when its compatible sister furnace is cheaper?

I get it, you like to keep it simple, simple practices, simple equipment, simple solutions.
Problem is, simple isn't always the best solution.
Back in the days of atmospheric vent, standing pilot furnaces, you'd have the same arguments. i.e. we don't need that spark ignition or draft inducer, it only adds extra costs and more parts to fail/stock.
In reality, these advances in the industry provided us with more efficient and safer furnaces. Same thing is going on now, new technologies are providing higher efficiencies and better comfort to an end user. There's no way around this simple fact.

Technologies change and you better prepare yourself to change with it. Or you'll be left behind trying to purchase that atmospheric vent, standing pilot furnace which is no longer manufactured, while your competition provides theirs clients with the latest technology.

Everyone I appreciate all the input and it actually has been very educational.