I need to see the space but IMO a portable is the only answer and you might need to alter his window or put a hole in the wall to accomaodate this and I get it we live in a MCM ranch no AC at all and we have one bedroom that always seems warmer than the rest I have no idea why but we have found if the person using that room keeps their door open it helps So he opens the window which faces S but we have huge overhangs and then leaves his door partially open and it seems to be pretty good at keeping the space liveable.

Have you had someone look at redoing the ducting? Adding additional vents in his room? What is the Insulation like?

A through-the-wall portable unit is the least expensive. Mounted high on the wall (cold air falls) with the addition of an elec outlet next to it. You might also research the "mini-split" units (Sanyo / Mitsubishi) which have several types of profiles (wall / ceiling mounts). Personal experience has shown that any house expanded beyond its original build almost always requires a complete re-do of the HVAC ducting to obtain efficiency.

You could try a "register booster fan" that sits in front of the duct's grill in his room. They run under $100. They plug into a normal outlet. An HVAC person can also adjust the dampers in the ducts so that the son's room gets more air when the a/c is on. If those changes don't cool the room enough, then try the good suggestions above.

How about using ceiling fans? Especially for your son's bedroom.

Ceiling fans for sure. Post some pictures of the bedrooms and I'll be happy to offer some suggestions.

I don’t have central air conditioning. Last year our window air conditioner stopped working. I purchased an LG free standing unit that we ❤️ love❣️it cools quickly and is energy efficient.

#1 DD has a free standing--if you can open the window you can use a similar unit. It cools her rooms well. Would having him change rooms work? It sounded like you have more than two bedrooms.

Thanks everyone for the ideas above! Very thoughtful. Unfortunately, a lot are non starters because of some unusual features of our old house. I don’t want to sound like I’m being negative by rejecting everything though!

First, I appreciate the comments about an old house and inadequate ducting. On further thought, the bedroom isn’t really significantly warmer than the rest of the house.... maybe just a degree or two. So I probably spoke too soon when I complained about it being at the end of a run. The bigger issue is just that son wants it in the 60s to be comfortable, which means blasting two big units all night to cool 2500 sf total, when he’s only using 150 sf of that. So I don’t think the solution is fixing duct lines or insulation.

Second, I’d like to avoid any permanent units (like a mini split) because the home is exposed block walls and architecturally significant. I think the architectural society would come with pitchforks and chase me out of town!

Ceiling fans are the perfect obvious solution.... except the middle of the ceiling Is where the one vintage air register is, and there is no power running through the ceiling. And even if I were open to moving it, there is no power running through the ceiling and no way to get it there. Because, as mentioned above, the walls are exposed block. Lighting is all from plug in lamps. So we cant run wires through the walls because there’s no drywall. I guess that also means no booster fan in the duct.

So given the extremely limited flexibility my vintage house provides, it sounds like my only solution is a free standing unit. Which I kind of assumed! Thanks all!

This house is in a warm climate (Florida). It was built in time when residences were not air conditioned by mechanical means.

The only way to make this efficient is to redesign the whole house HVAC.

Due to build factors when this house was built you might need 2 HVAC units. It's either that or upgrade the building shell (thermal envelope of the home). Heat load calculation will need to be performed.

{Warning: heat load calculations can be manipulated, easily goofed, over / under calculated due to the R-values of your thermal envelope... those R-values if not updated are often guessed at when performing said calculation. Put faith in who is doing the work they should have 'experience' in doing these kinds of jobs, not just a calculation and then find the cheapest installer you can find.} Design of the system(s) down to ducting, returns, layout, etc. also have a great impact on how well or not so well a HVAC system will work.

Florida is also a humid climate, which might be why your son sweats bullets. Temperature + Humidity cause a lot of problems.

This is an "in person type of job". It will likely require a substantial investment to correct.

If your goal here is to find ways like adding window units or portables to address this problem, it's one way but you're just putting band aids on a mortal flesh wound IMHO.

I service the Katy, Texas area.

I suggest Danfoss heat pump would be best choice.