I had a mini split in a freestanding building for a few years. If I were doing it again I’d just do a traditional system. While the mini split was efficient, I had a huge problem finding anyone who could or would service it. I would make it clear it was a mini split and then the guy would show up and say “oh I’ve never worked on one of these before” Seriously .It only lasted a few years, maybe 3 before it quit. Each guy who worked on it told me the previous guy was wrong in what they said or did. So when it died, the cost of running ducts in the now finished building was exorbitant so I had to put in a PTAC unit, which is the kind you see in hotels.

Get the opinion of another HVAC contractor that installs both mini-splits and traditional HVAC systems. They should be able to give you an unbiased opinion that is best for you and your structure.

We have Mitsubishi mini-splits in our Maui condo. Materials are not expensive, and they are not difficult to install. Our neighbor's Mitsubishi units are more than ten years old. I'd think you only need one, not two, in this new build.

Still, wouldn't you want A/C for the whole structure, not just the top floor? A whole-house traditional unit would be my choice then. It can be zoned.

The bottom floor is half patio, half storage/workshop, so does not need A/C (we'll have a wall unit in the workshop, but it won't be conditioned most of the time). I just mentioned it because it may be hotter up there than in my ranch house. I'll make sure to have the HVAC guy get a third-party load calculation.

I know that traditional HVAC can be zoned, but it seems like that raises the price to the same as mini-splits, with none of the accompanying efficiency of not losing air through ducts. Also, I have read that the dampers used for central HVAC are prone to breaking. Any thoughts on that?

In this setting, your biggest issue is oversizing. Traditional go down to 1.5 ton. Zoned typically start at 2 tons.

I know my mini (to be installed) is 9k or .75 ton and it modulates down to 3k. Your load is likely less than a ton unless you have some big west facing windows.

So what crazy oversized traditional system is this joker talking about putting in?

You save very little by zoning a small single story place.

David Cary, good point. But I can't find very small systems in mini-splits, either! I'll need one in my 90 ft2 office (which is separated from everything), and the smallest air handler I can find is 6K! Is this something that can be addressed by units that modulate down to a smaller number?

The zoning would be nice because the times the office is being used (9-5 on weekdays) is opposite the times the apartment will be used (mostly nights and weekends). If I have a traditional non-zoned system, I'll be heating and cooling the whole thing basically all the time.

If you have the traditional system put in you're looking at heating/cooling about 500sq ft with 1.5 tons (the smallest available). Yes, that's oversized in a well insulated building. I recall Austin can have a pretty humid climate so you may be compromizing dehumidification some.

Minisplits work well in open plan buildings but less so in spaces with multiple rooms. How will the apartment be configured? If it's multiple rooms - bedroom, kitchen, living areas, bathroom - then a minisplit/minisplits may not be the best solution (yes, you can zone them but it starts getting expensive).

Thanks, sktn77a. It is a one-bedroom apartment, open except for the bedroom and bathroom. There is a separate office across the hall. We were planning on three handlers - one in the 11x11 bedroom, one in the 13x23 main living area, and one in the office. I asked the HVAC guy to find a system with a low minimum output to try and compensate for the overload.

Oversizing and coverage is indeed an issue. If this were mine, I would put one PTAC heat pump (like in motel rooms) for heating and cooling in the living area of the apartment with a ceiling fan in the bedroom and maybe a second fan in the main room, and probably a through the wall mounted small "window" air conditioner heat pump in the office. If you want more cooling in the bedroom, put a through the wall mounted small unit in there too.

Because it moves the compressor outside, a minisplit will be quieter than a PTAC and much quieter than any window unit. Mitsubishi (Mr. Slim) makes decent minisplits. They are really very pleasant to use.

Getting a minisplit installed and serviced used to be a big problem here in the US. It's getting better, but we're still somewhat behind the curve. Most of the rest of the world, especially Asia and the Middle East, has been using minisplits for a good 20 years.

OTOH, a lot of US HVAC installers still think of them as data center cooling, sort of exotic and weird. They tend to price the installation like that of a central home air conditioner.

For HVAC dealers in other countries, minisplit installations are routine and much cheaper. From what I've been told by friends, if you buy one in Uruguay, your installation will cost around $100-200. In Puerto Rico it'll be $300-400.

Tl;dr: the minisplit will be more expensive than it should be, but I think you'll like it.

What does PTAC mean?

A search suggests minisplits came out in the 1970s.

I've used them overseas and they work just fine. In the US, they're expensive for what you get and finding a contractor with enough experience to service them may be a challenge. The standard install with the near-ceiling wall mounted unit isn't attractive. Some companies make ducted minisplits now that improve on the aesthetics. Maybe a ducted system with zone control would be a good choice but I'll bet it would be very costly for such a small space.

Keep in mind that mini-splits can make a room look like a cheap hotel room, but they can be disguised with careful planning.

There may be some good PTACs out there, but most are noisy and unattractive, just like the cheap motel rooms where they are used.

There are lots of variations for mini-split heads that install in the room, including some that are recessed and look like traditional vents and others that allow you to add ducts to cover more than one room. They are not all just a single head mounted high up on the wall.

The most common complaint I've heard about mini-splits is that the installation is supposed to be easy, but installers charge as much as they do for a traditional ducted system, or maybe even more. HVAC companies don't work with them often, so they pad the installation cost to cover the risk that something will be more complicated than expected.

Bruce

So a PTAC is basically a through-the-wall window unit with heat pump capability, right? (I realize any air conditioner is a heat pump both most cannot be reversed to pump heat INTO the conditioned space!).

I am not going to tell you what to do, only point out some things that most people don't consider. If you think that minisplits will save money by conditioning part of a new modern, well-insulated structure (zoning), forget about it. Heat and humidity move from room to room much faster than inside-outside. Furthermore, the attic is gong to be sealed and the insulation at the roof line, it is a good place for ducts, HVAC equipment and your water heater. Electric furnace? Why not a heat pump if he is proposing ducts anyway? Get an energy rater to do some work for you. If you have a building with a very high performance envelope (insulation and air sealing) worrying about and spending a lot of money on high efficiency heating and cooling appliances might be misplaced.

Capacity modulation is great, but when you move from 1:1 indoor:outdoor units to multiple indoor, you lose some. I think they all throttle down to about 30% on the compressor side. Installing two or more on the same outdoor unit limits the final low capacity. If you want to throttle back to the lowest capacity possible, you will use 1:1 systems. I don't know if anyone pays attention to this subtle fact. It can mean a big difference in how a house will perform. For example, putting all bedrooms on one of two outdoor units means that at night they might all throttle back to 30% before they start to cycle. If all three are installed on different compressor/outdoor units, they may not be able to modulate much at all.) After switching from ducted system to mini splits, I don't miss cold air blowing in the bathrooms. Heat would be another story entirely.