I have a 45 year ranch style, single level, 1400 sq. feet house in San Jose, CA. I had 45 year old day & night down flow furnace and no AC. I replaced it with Trane furnace and new Trane AC. I was paranoid about age of the system and thinking that duct work must be in bad shape, I got duct work changed as well. That seems to be mistake I made. I have following questions on duct work and I would like opinion from HVAC experienced guys like you on this forum. I am a first time home buyer, so I am not well conversant with correct terms.

1. Return duct is in Attic. Supply ducts are in very short unfinished crawl space. Crawl space height varies from 12 inch to 22 inch max. All new duct work is flexible duct. Trunk and return ducts are black thin plastic from outside whereas plenum is silver from outside. Duct work is laying on ground. Crawl space is unfinished but 99% it is plane. Is it OK if duct work is not supported and secured to joists? What are disadvantages? Is this violation of code? Will I make it worse if I ask contractor to make it hanging which may introduce more turns? Or should I leave it as it is on ground?
2. Contractor did not put any dampers to air balance ducts. He actually cramped some of the ducts to reduce air flow from those. What are issues with this approach?
3. 2 bathrooms have the maximum air flow whereas 2 bedrooms have minimum air flow. Bedrooms are furthest. So contractor has asked me to keep bathroom registers completely closed because even after completely closing enough air still comes out of gaps and holes. I think this will put extra load on blower but I would be interested to know how much extra load it will be. Any ideas?
4. Originally some registers were 2 inch by 12 inch. Contractor new boots of this size are not available any more. He replaced all (except 2 in bathroom) to 6 inch by 12 inch. Wouldn't this cause lower air flow in last two bedrooms? Contractor's argument is that new blower is powerful than old one and hence it is fine.
5. When holes for registers were made bigger, workers actually have cut floor more than boot would need. This has created a wide opening on sides of boots. When I showed it to him, he has plugged those opening with silver duct tape. Is there a better way to handle this situation?
6. What options do I have to make sure duct work performed is up to the standards and codes? I do not think another HVAC contractor will do inspection.
7. Another thing I am not happy is that he installed AllStyle AC coil instead of Trane. In the agreement, it was not clearly mentioned as to which brand he will use and I was under impression that he would install Trane coil as he is Trane dealer. Anyone knows if this brand (AllStyle) coils are problamatic or not?

Thank you very much for reading lengthy post. Any help is much appreciated.

Sounds like you got the run around and that's putting it nicely. As far as the flex duct I would run and run fast from it. It will come apart intime then you have the labor and supplies for the repairs. The flex return will fail first then the supply flex duct on the ground will go next if your lucky you will notice it before you heat and cool the area outside your home. Its people like that, that give people like us a bad name.

It sounds to me like your heating contractor did some really shotty work, yes all flex should be supported. Yes, they do still make a 2" by 12" floor boot. Did he run any ductwork at all? How big is your bathroom? I would say a 6" by 12" is way too big for your bathroom to start with. I seriously think you need to get the contractor back to redo this work, or have another contractor fix his mess and maybe seek legal action.

Yes, they do still make a 2" by 12" floor boot. Did he run any ductwork at all?, How big is your bathroom? I would say a 6" by 12" is way too big for your bathroom to start with.

Sorry it was not clear in my post. He has not changed bathroom registers/boot as those were 4" by 10" and 4" by 10" inch are available. Registers in living room, family room and 4 bedrooms are changed to actually 6" by 14". He did not run any calculations and simply changed all in above rooms to 6 by 14. Living room and family room are big around 17' by 11' but 2 bedrooms are small about 9' by 9', 3rd bedroom 9' by 11' and 4th bedroom 11' by 10'. Bathrooms are about 5' by 10'.

Sounds like you got the run around and thats putting it nicely. as far as the flex duct I would run and run fast from it. It will come apart intime then you have the labor and supplies for the repairs. the flex return will fail first then the supply flex duct on the ground will go next if your lucky you will notice it before you heat and cool the area outside your home. Its people like that, that give people like us a bad name.

I agree things are in screwed up state. I do not have option of running away from Flex because it is already installed. I wish I would have visited forums before I got work done. Now it won't be practical to install rigid piping without significant work. What I am interested in is to prepare list of things that can be fixed with reasonable effort and have contractor fix it to make situation little better.

The only way that you will ever be able to fix your airflow problem is by having the ductwork properly sized and installed, if you don't you will have many years of trouble with your system. Not to mention bad airflow will take years off your furnace. Newer heat exchangers cannot handle bad airflow , for example - if you don't have enough air moving across the heat exchanger it will cause the furnace to overheat and very quickly ruin the heat exchanger. I'm sorry to have to tell you this but you need to fix the problem otherwise you will be replacing the system a lot sooner than you should have to.