Friend if you attic never get's above 125F waaaaay above,don't mess with it.

Thanks for your note. I suspect in the hottest zones it gets to 130 or so in the hottest parts of it and then the rooms below that hottest area are very hard to cool down at night. The attic ventilation contractor says that with the above, they could reduce the attic high to 105-110. I suppose the questions are

1. Will it?

2. Even if it does, how much of that translates down to easing of the cooling of rooms below

3. Does it meaningfully reduce the load on A/C and my energy bills.

If it was a 1-2k investment, I wouldnt bother but the quote is much higher.

To answer your questions: 1. Yes, it will reduce the temp to 105-110, I did that for my home. But I have power fan, much more stronger than solar fan. 2. That depends on the type of ceiling insulation, I have 18 inch of insulation above my ceiling, so high temp in the attic won't affect much of the room below. another words, not much benefits for me. 3. It will reduce the overall AC load if your air handler is in the attic, again, it depends on how well your AC box and ducts are insulated.

No one can give definative ansewrs without assessing the intire structure but here's a few toughts to kick around. Having adiquate insulation is singlemost important followed by ventilation. You mentioned having blown insulation now and contractor saying soffit vents should be replaced. It's possible existing vents are covered with blown insulation. It's also possible blown insulation is blocking air space between roof deck and wall top plate where rafters and ceiling joists sit on top plate. Unless soffit vents are of poor quility,damaged or clooged with paint,I don't know why replacing them would help. Adding additional vents might help but why would old one's need replaced? I suggest you look or have someone you trust look for improper installation of insulation as I mentioned above. You stated attic has "A" whirlybird type vent. Only one? I'd expect at least 4 on 2400 sq ft. Pulling whirly topper and replacing with solar power topper is a handy diyer job at best. A solar powered or 120 volt fan is a worthwhile improvement over conventional wind powered whirly topper. There is debate over radiant barrier if added after construction is complete UNLESS done in conjunction with a re-roof. Not my field of expertise but some say dust soon covers add on barrier rendering it useless. I have mixed feelings so I suggest you research. the matter.

@Cima Locert and @klem1 - thanks so much for your valuable commentary - 🙏. Even though the contractor I got the bid from "feels legit" - there are always a lot of lessons to be learnt from folks who actually got the work done and who have nothing to gain from selling you - often if you are a hammer, everything looks like a nail !

@klem1 - to your points

1. Some soffit vents seem clogged. There are 24 or so of these around the house so there seem to be plenty. He showed me a few that are clogged but didnt quite tell me why (blown insulation may have gotten into some - as you mention) or whether they can't just be cleaned. Either way - this is a relatively small investment ($500). They are definitely old (~15 years) so I can buy into the argument of replacing them.

2. Yes , there is only one whirlybird vent at the moment and the part of the house which is closer to it - seems to cool down fine (that part also doesnt get the afternoon sun as much). I am buying into the idea of replacing the whirlybird with solar and adding at-least one or two more solar fans while we are at it.

3. Great point on dust over radiant barrier - hadn't thought of that.

4. @Cima Locert - your point that if attic is well insulated with blown in, it should have minimal impact on room below is making sense. My A/C housing is in the attic so I suppose it would help some there but it doesnt seem like worth spending several thousand dollars!

Net-net, I am going to forego the radiant barrier (especially since installing it means having to re-do your blown in insulation which doubles the cost!) . Just add 2 solars and take it from there.

Thanks again - I hope this information can help other people in the same boat.