Yeah, it is clear that these are oversized. I believe that on the tax record, the sqft for the top 2 levels is 3500sqft. The bottom is probably another 1200sqft, to make it 4700. Obviously way overkill for this system. I'm not even sure what the top unit is, but I'm sure it is probably a 3ton system up there. I agree that if I had a person I trusted in the area to do a true assessment, and size it as you state above, I would be all for that. I just don't know if I trust the regular HVAC guy off of the street to not just push what has the greatest margin. We also want to move in the next 3-4 years to the home we are redoing in Delaware, so I'm not sure sold on putting in a new system for that reason.
There is clearly zero financial "payback" on a new system, so just patch the ridiculous beast and be happy.
Efficiency-wise a ludicrous oversizing factor isn't much of a problem for hot air furnaces- it's primarily a comfort thing. For heat pumps and air conditioners it's far more important to size it correctly to optimize both the efficiency and comfort.
You know something that I like in this other site that I look at for VW diesels. They have a link in there for trusted mechanics that is broken down by areas. So I can find someone in the local area that seems to have the experience to work on VW Diesels. There probably isn't enough demand on this site for trusted HVAC guys like Nate.
Nate Adams isn't even an HVAC guy. He was originally an insulation contractor getting most of his work referred through state subsidized weatherization programs. But he's not an idiot, and saw that people were only paying for what was subsidized, when there were often more glaring and obvious issues creating their comfort problems than mere insulation. When he got sick of how those programs were working against the best interest of contractors and homeowners alike he re-adjusted his business focus and took a more holistic approach, selling comfort rather than R-values or BTUs, targeting a more receptive & better-educated/savvy/aware types of customers than the folks who would only consider state subsidized upgrades in a piecemeal fashion, missing the bigger picture.
He wrote couple of blog bits about his business transition on the GBA site about five years ago:
https://www.greenbuildingadvisor.com/article/the-low-hanging-fruit-fallacy
https://www.greenbuildingadvisor.com/article/hard-truths-of-home-performance
They recently reviewed his book on that site too:
https://www.greenbuildingadvisor.com/article/energy-retrofit-advice-from-ohio
Very often comfort & efficiency issues aren't directly HVAC related at their core, but the HVAC and house really need to be considered together as a system, and adjust things accordingly. Most HVAC contractors only address the HVAC equipment, and most are pretty bad about sizing it for the load, erring to the sub-optimally high side "just in case" there's a cold snap where it bottoms out a -150F or colder.
Even though truly grotesque oversizing is pretty common, I still find it jarring when I see a 90K furnace serving the 10-15K load (of a 1200' first- floor). The design heat load of a typical 2x4/R13 reasonably tight 4700' house with clear glass double panes in Virginia would run about 40,000-50,000 BTU/hr (for the whole house) to maybe 55,000-65,000 BTU/hr if it has an unusually large amount of window area. (If it's a lot more than that the house probably leaks as much air as a wind-tunnel, a defect that's usually pretty cheap and effective to bring under control by addressing the largest or most important air leaks.) To max out the comfort with a hot air furnace the oversize factor needs to be no more than 1.4x the load at the 99% outside design temp. So even for an over-glazed 4700' home in your area the 90K furnace would probably be sub-optimally oversized even if serving the whole house.
I have some in-laws in central MA with an overglazed ~4000' "mid century modern" type house built around 1960 or so. When they bought it there were separate 5 ton and 4 ton commercial building type air conditioning units on the very low-angle roof (with a nightmarish scuplture of ductwork above the roof, not quite visible from the street) and a 200,000 BTU/hr boiler in the basement for radiant ceiling heat throughout. The equipment was capable of satisfying the thermostats, but the place was downright miserable in winter, even worse in summer. Their first major investment was to replace most of that glass with current code minimum low-E double panes, which was necessary, but not sufficient. It nudged the needle a bit but they were still miserable, and considering selling the place an moving on.
After consulting with them and taking a hard inspection tour of the house I talked them into taking a big financial gamble on building a whole new roof structure over the mostly flat roof creating a very low gable with 6" of continuous rigid polyiso under a membrane on the outside of the new roof deck, mothballing the boiler and installing a right-sized multi-stage gas furnace & right-sized AC with all of the mechanicals & ducts in the micro-attic (less than 3' tall at the peak) between the old and new roofs, with the sizing based on a full Manual-J calculation performed by an engineer. They ended up with a 60,000 BTU/hr condensing gas furnace and a 3 ton split AC, literally 1/3 the capacity of what had come with the house, and for the first time since the house was built it's now actually quite comfortable year-round, and you can only hear the heating/cooling system when it's dead calm outside, with nothing going on indoors.
I doubt that there are
any HVAC contractors who would have steered them in that direction, but Nate Adams (probably) would have. The HVAC was just the frosting on the (fairly expensive retrofit) cake, but it's now a nice house to live in, not just to look at.
