I called four AC firms to ask if they could help me to pull permit. Three said "no", the other said the conservative estimate is $2000. I have another guy coming in this Friday to take a look and get me a quote. They told me that the new requirement is nonsense because the county ask contractor to put their name on the line then in the end the manual J is not required. No responsible contractor would risk that so the manual J must be done. The one quoted me 2 grand will do manual J (could cost cost more depending on the result!).
I know it's still pandemic pricing, but 2 grand for a Manual-J is ridiculous,
especially if it's an HVAC company doing it, unless you have the oddest collection of non-standard construction where U-factors have to be separately calculated and entered. If it's an 'merican style post-1945 stick built house with a poured concrete or CMU foundation with normal windows (any vintage) and doesn't have a completely weird shape like 17 corners to the footprint and a dozen odd dormer it
should be under a grand (normal times), but probably still more than $500.
I will tell my inspector that I will seal the vents that I installed and put up drywall without cutting the vent so there is no "mechanical extensions to finished basements or alterations to an existing system". I will not install doors to the rooms that I originally framed out so all the space will be connected except bathroom having a door. I can cut out the vents and install doors after the county signs off the final inspection.
Of course I might need to revise my building permit to remove these doors, but it is only $50 filing fee.
Reversing your duct modifications gets rid of the extension issue. Do finished basements required by code to be heated & cooled? What does removing the doors buy you, exactly?
Whether somebody else does it or you do it, it's still worth running a room by room Manual-J on the place to know where you are with it, and to be able to plan for comfort. It doesn't take a lot of time. While online Manual-J-ish tools like
LoadCalc &
CoolCalc are like somewhat stripped down versions of a pro tool, in the hands of newbies it's easy to screw it up. The
BetterBuiltNW HVAC tool is simpler and easier to use (but with Manual-J underpinnings) and still seems to give reasonably accurate load numbers. (I've only used it on a single project so far- I haven't pushed it's limitations very hard.) A primary difference between BetterBuiltNW and the others is that it uses reasonably
aggressive defaults on U-factors & air leakage. It also has a duct design portion (that you should probably ignore unless you know what you're doing.)
The target audience for that tool was for HVAC pros installing heat pumps. The chronic oversizing thumb on the scale that most HVAC installers have doesn't lead to efficiency problems when the equipment is hot air furnaces (although there are often comfort consequences from 2x+ oversizing), but oversizing heat pumps has compounding issues of significantly higher upfront cost, significantly lower as-used efficiency, as well as lower comfort.
If you run room by room load calculations on both the basement and the rest of the house you'll probably find that your AC is more than 1.5x oversized, and the furnace more than 3x oversized. (If I'm wrong, be happy!) ASHRAE recommends no more than 1.4x oversizing for hot air furnaces (rarely found in real houses unless the equipment was specified by an engineer, not an HVAC contractor). With cooling 1.2x is a better oversize factor to use for single or 2 stage system, but with modulating systems with a 3:1 turn down or greater it's still fine at 1.5x. Above that efficiency & comfort tends to fall off. AFUE testing on hot air furnaces uses a presumptive 1.7x oversize factor, an oversize factor that's still fine for efficiency, but is a bit lacking from a comfort point of view (unless it's a 2 stager).
Sizing your basement heating air flows to be the same oversize factor as the furnace & flows are to the rest of the house would make it track sort-of reasonably operated as a single zone in the middle of winter, but the basement cfms may need to be tweaked upward during the shoulder seasons, since basements don't get much solar gain benefit, and has the constant heat draw of the cold basement slab (unless you insulated the slab.)