Mitsubishi shows floor mounted and horizontal concealed duct air handlers. Link.

Be prepared that you won't find many HVAC companies that have experience with designing and/or installing these systems.

@chispa In the San Francisco Bay Area, there are a good number of firms that deal with large mini-split vendors. The problem is they all want to do $25K+ installs. That's a hard pill to swallow when you see the Chinese knock-off products selling equivalent capability for about $6K to $8K in equipment cost through Home Depot. These are apparently very high-margin products for the installer.

@dan1888 The problem with that Mitsubishi design is it places a large air handler below the floor. How are you going to change filters and do maintenance to that unit? That is going to be expensive maintenance in the crawl space of the home. I was imagining a unit that would slide down into the existing grille and have all of the key service points (like filters) accessible from the top by lifting out the grille.

Probably I would go for a floor-mounted unit that puts the entire air handler inside the home before I would use the Mitsubishi horizontal-ducted units. But that gets into aesthetics again and might lower the resale value of the home.

@chispa That is just an overview of mini-split systems, but it does not discuss the question I raised.

It shows the self contained unit that goes flush in the ceiling and isn't an ugly wall wart ... I've never seen a floor unit offered when I did some research on these systems. The flush units can also be placed vertically in a wall.

I don't see the room to manage intake and exhaust efficiently in the dimensions of the single floor vent you pictured. And configuring a crawlspace to be usable is fairly common. 6-10mil plastic with pea gravel and lights is what we have under the cottage. It's easy to do things similar to changing a filter. No expense at all. I'm not seeing significant enough drawbacks to the Mitsubishi components to derail the possibility of success. So far it seems to have the highest positive probability.

@dan1888 The grill could be removed and replaced with a larger in floor footprint based on the same idea. So I am sure what I am asking for could be designed.

I asked a specialty vendor to quote on make the crawlspace more usable as you describe, and they wanted $20K for that. Everything has a cost. Even after I spend that $20K, vendors will refuse to do work in a crawlspace and will make that a reason to charge two or three times as much for maintenance, if getting into the crawlspace is required to change filters on each individual air handler that is mounted under the floor.

The money a busy contractor asks for a one off project can be priced so that you don't choose to do it and they don't have to use their time for something they're only going to do once and have never done before. . . I've seen it before. A fence contractor was asked to quote an unusual property. He threw out a price he felt was ridiculous but got the job and was happy to make a bundle. . . . I price materials first. Well, first I find out what's necessary to do the best job possible. This also helps to evaluate contractors. Then I price the materials. Then estimate the time necessary and any special tools/machines necessary. . . . .In the case of a crawlspace you'll need to access 2-3 times a year, well that's realistically not much of a hardship. Light and 'finished' paths to the air handlers. You're not going to live down there. . . . .You can come at this project from a minimalist point of view to establish a base budget. No need for LVP down there. Tailor things for the primary purpose. Remember, you're perfectly satisfied with the present unimproved condition you have at present.

This type of evaluation of home improvement work is likely going to become more of the norm for a while. There aren't enough contractors to make pricing favorable for the homeowner.

@dan1888 The contractor that quoted me on the crawlspace improvement specializes in crawlspace improvements. That is their whole business focus. So I don't see any point in doing a $25K mini-split system that also requires a $20K crawlspace improvement. This is particularly the case when the outdoor and indoor equipment can be purchased for around $8K at Home Depot.

Finding ways to make equipment easy to install is a key component in making a system's overall costs lower than competitors'.

In my area, going into a crawlspace alone is something like an OSHA violation, so a filter change by a company would be more costly - they always need a second person around. Would only matter if you couldn't change your own.

Why not just use a ducted mini in the crawl? Install it yourself or find someone to do it.

Want to get frustrated with costs? I have a ducted mini in an attic to cover the master suite - 1 return, 4 or 5 supplies. 1 ton Mitsu. $3500. New construction. Part of a $15k total install of 3800 sqft. 2 trane HP - 2 tons each.

My point is also that the amount of money is high but maybe worth it for you. The fact that it is all a rip off is somewhat irrelevant if you have no other option. The simplest would be the cheapest which I suspect is a self installed mini. If you really wanted value, you would move...

@David Cary Any inside unit for a mini-split will have the filter at the inside unit. If I put a ducted mini-split inside unit in the crawlspace, I still have the filter change problem.

So you put 4+ supplies in the master bedroom alone? That's actually a clever design to dedicate one zone of the mini-split to that room and then partition the supply to different points in the room. How did you partition the supplies across the master bedroom? I could see two in the main bedroom, one in the closet, and one in the bathroom, although that might create a vacuum if the bathroom door is closed.

Master bedroom aside, the cheapest implementation I can see so far would be floor-wall-mount indoor cassettes, and you could place those right above the existing in-floor grilles so that it would look like a more natural continuation of the original home design. The drip tubes from those wall-mounted cassettes could be run straight down into the crawlspace, saving an outside wall penetration. The filters would be inside the house and therefore easier to change. That is still significantly uglier than what I want. If cost were no object I would do it differently.

@David Cary I like your approach with the horizontal ducted units in the attic. That lets you put multiple supplies and a separate return in every larger room, significantly increasing comfort. My attic can be accessed by a ladder and has plywood flooring so that would be much easier to access as well.

Do Gree, MRCOOL, or any of the similar cheap Chinese brands have horizontal ducted units that can go into an attic?

Yeah - 2 in bedroom, 1 closet, 1 bathroom. The doors aren't tight enough to cause an issue. The mini moves less air than typical - especially spread over 4 supplies - so airflow/vacuum issues are not a problem.

Our filter is in the ceiling. The ducted mini's do not have filters on the unit.

Interesting, with our new house, I find the filters are good for about a year. I think it is partly that we have a lot of filters and partly that the house is tight so the system doesn't need to run that often. We are in NC which needs longer heat run times than cool by just a bit.

@David Cary So the Mitsubishi horizontal ducted units have to be connected inline to a separate filter box? That's surprising that they would not integrate the filter, but it is not a big show stopper.

How many square feet are you conditioning and how many air handlers?

@ranchtastic 2100 square feet but five distinct zones. The home leaks and has original windows, so getting the house to any kind of uniform temperature without zoning is impossible. I plan to move within the year so I want minimum investment in a system required to sell the home while trying to avoid buyer remorse/complaints about heating/cooling issues. I know a five-zone mini split - if done in a way that is not an eyesore - will be incredibly efficient and incredibly comfortable.

I think they design it so the filter is the easiest to change - ie not in a crawl or attic. You can always put the filter next to the unit (with an added box) but the ducted models are not designed to hold a filter. Whatever you do, make sure the filter is thin because the minis don't move a lot of air as it is.

@David Cary The cassette units definitely have filters in them don't they? The Mitsubishi marketing for the wall mount units here says "Advanced filtration features deodorize and purify the air in your home, contributing to better health." Having at least a simple level of filter seems like a must-have thing for any HVAC system. For mini-split, the technology is such that the filter must be at the indoor unit or it is nowhere at all.

@David Cary Can you explain how the zone temperature is set for the master bedroom horizontal ducted indoor unit? Are they using the same wireless controller they use with the wall-mounted solution? Or is there a hard-wired controller in the wall that goes to that horizontal ducted unit to set limits for the zone?

The Bay Area real estate market is hot hot hot. Depending on the condition of the rest of your house I doubt this investment will make or break a sale. And I'd be hesitant to throw this much money at a house I planned to sell within a year.

@ranchtastic The existing HVAC does not work at all, and the zoning is so awful that even if it worked it is extremely uncomfortable. If I can remediate this issue for under $15K I just do not want a big item that might steer a potential buyer away.

In a similar way, I have 40 year old carpets that look toxic. Ideally I want to get those replaced with a decent light colored wood because I do not want someone looking at the carpet and thinking that they would never want to live a day in that condition. The floors I can do under $10K.

$15k seems light in the bay area for a complete overhaul of HVAC.

Looking up the equipment costs for the Mitsubishi, you're going to spend most of that just buying the cassettes and the mini split, let alone other materials and labor, which will cost at least as much. Not too many non high tech workers can afford to live in the bay now, so you are paying for their commutes/cost of living.

@ranchtastic The system I want at full retail would get quoted $25K to $35K.