Do what all the insulation contractors up here do - cut a few vent holes in the roof- blow in the insulation, and install roof vents.
Walls can be a bit more trouble - but depending on the type and condition of the siding it is common to remove the siding, cover with
2" Styrofoam SM or equivalent, and stucco or re-side.
Ding ding ding! We have a winner. Without a manual J you are just guessing. Install companies always estimate too high, and deliver oversized equipment, which is the worst thing in a humid climate.
If you've done a manual J, and you have a number for what your load is supposed to be, theoretically you could test it.
You could keep track of the run time of your equipment and the degree days, and see if you got it right.
I have never seen this done, in either residential or commercial. That is strange in commercial where you have DDC control and can track actual flows and heat transfer - maybe design engineers don't want to know.
My crystal ball is cloudy. I think you should pay me 20k and I'll get er done for you....
I can monitor my run-time - and do on occaision as a sanity check. My conclusion is my 35000BTU furnace (on low fire) is slightly oversized 90% of the winter, and my AC is at least 50% oversized - just about what the Manual J predicts. I had not run the manual J untill the other day - and I knew both were oversized when I installed them.
The furnace, as I noted previosly, was the smallest residential furnace readilly available when I had it installed, and the AC was a free unit I installed to replace a 35+ year old unit that was still working. The free unit was only a couple years old when a neighbour changed out both furnace and AC for some unknown reason.. I scrapped mine instead of his. Mine was getting "a bit long in the tooth" and I figured it would need replacing soon anyway.
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