In my city, any addition requires a separate HVAC permit which includes a heat loss calculation performed by an HVAC engineer. This takes into account glass area, type of insulation, volume of the space, etc. Was this done in your case, or did the contractor just 'figure it out' himself? Was the insulation inspected during the course of the renovation? If everything was done to code and inspected there shouldn't be any problems.

Frankly, the addition of booster fans sounds like a 'hack.' Properly sized HVAC ductwork should not need this.

It is more about wall orientation [like North], amount of glazing [ windows ], attic wall insulation, delivered cfm vs load and return size. Booster fans deal with long runs and rarely solve anything.

100% yes to insulating the bedroom floor/basement ceiling. It has always made a world of difference in our situation.It’s very possible your perception of temperature differences is due to the floor being colder. Cold feet = cold body

You've tried to balance the system by dampering down ducts leading to other rooms? Usually you can force more air into an area if there's adequate ducting and volume in the system.

Were the walls, ceiling, roof and floor insulated? Does the insulation meet the requirements of your climate zone? If not, this could pose a problem even if your hvac system is adequate.

Thanks all! The walls, ceiling/attic are newly insulated, and actually went beyond what local code required - the only debate that went on was whether to add a vapor barrier to the attic insulation (which we did end up doing). It all passed inspection without any issues - in fact the inspector commented on the amount of caulk used in every single crack. :) It is a north and east facing room, and it does contain a large patio door as well as two average windows. The door and windows are fairly high quality (Anderson double pane/high efficiency) and I don't feel any obvious signs of cold air coming in/drafts, but this is certainly a consideration.

My city didn't require a separate HVAC permit - the ductwork was fairly simple (or so it seemed!) so the contractor did it himself, though he has offered to bring in an HVAC expert now, which sounds like might be what's needed.

I am not a heating expert much less a forced air anything. But I have done lots

of reading on understanding my hydronics system in the course of that, I read lots of other stuff. Most what I have gleaned are

boards large numbers of professionals

The replies above agree with what I have gleaned from other sites Booster fans are basically useless. The other caveat and others have said above is that any remodeling needs to include as part of that renovation and quote a proper evaluation and design of HVAC to properly heat and cool the space starting with a calculation of the actual heat loss based on the actual construction not sq ft. Once that is done then the ducting requirements can be calculated to deliver the amount of BTUs to heat and cool. This would likely require modification of the ductwork back to the furnace. You do need to get a HVAC pro to do the heat loss and come up with a plan .

I am looking into remodeling my kitchen and one one the requirements for a building permit is the design of the space heating for the new kitchen